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Distribution Category:Energy Conservation--
Industry (UC-95f)
ANL-85-66
ANL--85-66
DE86 007010
ARGONNE NATIONAL LABORATORY9700 South Cass Avenue
Argonne, Illinois 60439
TUBE VIBRATION IN INDUSTRIAL SIZE TEST HEAT EXCHANGER(22 ADDITIONAL CONFIGURATIONS)
by
H. Halle, J. M. Chenoweth,* and M. W. Wambsganss
Components Technology Division
December 1985
*Heat Transfer Research, Inc., Alhambra, CA
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A major purpose of the Techni-cal Information Center is to providethe broadest dissemination possi-ble of information contained inDOE's Research and DevelopmentReports to business, industry, theacademic community, and federal,state and local governments.
Although a small portion of thisreport is not reproducible, it isbeing made available to expeditethe availability of information on theresearch discussed herein.
3
CONTENTS
Page
NOMENCLATURE ......................................................... 6
ABSTRACT............................... ......................... ... 9
I. INTRODUCTION.................................................... 9
II. BACKGROUND ...................................... .............. 12
A. General .................................................... 12
B. Vibration Response.....................4................... 12
III. TEST DESCRIPTION...................................,......... 15
A. Test Exchanger and Flow Facility........................... 15B. Test Configurations...... ............... ......................... 18
C. Test Parameters/Instrumentation/Data Processing............ 18
D. Test Procedure......-....................................... 22
E. Critical Flow Conditions.................................. 23
F. Vibration Response Criteria................................ 25
IV. FLOW TESTS..................................................... 27
A. 45* and 600 Layout, 6-Crosspass Configurations(Cases 27-34) .............................................. 27
B. 30* and 90* Layout, 7-Crosspass Configurations
(Cases 35-38) .............................................. 38
C. 300 Layout Double-Segmental Baffle Configurations
(Cases 39-42).............................................. 45
D. 450 Layout Double-Segmental Baffle Configurations(Cases 43-47).............................................. 51
E. Simulated U-Tube Configuration (Case 48)................... 60
V. PRELIMINARY EVALUATION......................................... 61
VI. PRESSURE DROP MEASUREMENTS..................................... 66
A. Test Procedure............................................. 66
B. Overall Pressure Drop...................................... 72
C. Pressure Distribution...................................... 73
D. Analysis n.................................................. 73
VII. CLOSING REMARKS ................................................ 75
ACKNOWLEDGMENTS ...................................................... 75
REFERENCES ........................................................... 78
APPENDIX: Summary of Sensory Observations: Cases 27-48 .............. 80
4
FIGURES
Page
1 Test exchanger installed in Flow-Induced VibrationTest Facility.............. ........................... .... 11
2 Test exchanger tube bundle in 90 square layout,7-crosspass configuration.................................. 11
3 Test exchanger in 6 crosspass/5 baffle configuration....... 28
4 Schematics of typical 450 and 600 test configurations...... 29
5 Test exchanger in 7-crosspass/6-baffle configuration(Case 37 shown) ............................................ 40
6 Schematics of typical 300 and 900 test configurations...... 40
7 Double-segmental baffled tube bundle during assembly
(Case 39 shown) ............................................ 46
8 Double-segmental baffle arrangement and orientationcombinations ............................................... 46
9 "est exchanger in 6-crosspass, double-segmental baffleconfiguration (Case 40 shown).............................. 47
10 Schematics of 300 double-segmental baffle testconfigurations ............................................. 47
11 Test exchanger in 6-crosspass, double-segmental baffleconfiguration (Case 45 shown).............................. 52
12 Schematics of 450 double-segmental baffle testconfigurations ............................................. 52
13 Principal observations of double-segmental baffledconfiguration tests........................................ 54
14 Tube bundle of simulated U-tube test....................... 62
15 Test exchanger in simulated U-tube test configuration( Ca se 4 8) .. 4. ..... .. .. .. .. . ... ..... ... .. .. ........ .. .. .. . ... 6 3
16 Mode shapes of 3-span simulatedU-tube..................... 63
17 Location of pressure taps.................................. 68
18 Details of nozzles and pressure tap locations.............. 71
5
TABLES
Page
1 General features and basic dimensions of test exchanger.... 16
2 Tube and tube bundle specifications............................17
3 Test cases and configuration code.......................... 19
4 Flowrates associated with instability and tube impactingor with large vibration amplitudes at different locations
in tube bundle. Cases 27 to 29....... ................ 31
5 Flowrates associated with instability and tube impacting
or with large vibration amplitudes at different locations
in tube bundle. Cases 30 to 34............................ 32
6 Critical flow parameters of 450 and 600 layout, 6--crosspass test exchanger configurations... ................. 33
7 Flowrates associated with instability and tube impacting
or with large vibration amplitudes at different locationsin tube bundle. Cases 35 to 38............................ 41
8 Critical flow parameters of 30* and 900 layout, 7-crosspass test exchanger configurations.................... 42
9 Flowrates associated with instability and tube impactingor with large vibration amplitudes at different locations
in tube bundle. Cases 39 to 42............................ 48
10 Flowrates associated with instability and tube impactingor with large vibration amplitudes at different locations
in tube bundle. Cases 43 to 47............................ 53
11 Critical flow parameters :f double-segmental baffledtest exchanger configurations.............................. 55
12 Virtual mass and natural frequency calculation............. 65
13 Comparison of groups of corresponding test configurations.. 67
14 Overall pressure drop versus flowrate...................... 74
15 Pressure drop distribution................................. 76
NOMENCLATURE
6 1
Symbol
D
f
L
mact
my
P
Q
U
U
Un
UCR
V
z
a
apY
am
p
Subscripts
CR
n
Configuration Code
NOMENCLATURE
Description
Tube diameter
Vibration frequency
Internal length of shell
Mass per unit length of tube
Virtual mass per unit length of tube
Tube pitch
Flowrate
Mean crossflow velocity through minimum gap
Reduced or nondimensional crossflow velocity, U = U/fD
Effective crossflow velocity, see Eq. 2
Reduced or nondimensional critical velocity
Nozzle flow velocity
Distance along length of tube (from inlet tube sheet)
Exponential variation of pressure drop with flowrate
Instability threshold constant
Pressure drop constant
Pressure drop, overall, inlet-to-outlet
Mass damping parameter = mv21c/pD2
Equivalent viscous damping ratio
Fluid density
Critical, based on experimental data, at lowest flowrateinitiating instability
Pertaining to mode n
3 core and 2 wing bafflesC
8
D
F
N
P
U
W
6, 7, or 8
10" or 14"
300, 450, 600,or 900
16% to 30%
PC or TC
Double-segmental baffles, full bundle, plain tubes
Full tube bundle (single segmental baffles)
No-tubes-in-window bundle
Plain tubes
Simulated U-tube bundle
3 wing and 2 core baffles
Number of crosspasses
Nominal nozzle size
300 triangular, 450 rotated square, 600 rotatedtriangular, or 90* square tube layout pattern
Baffle cut as percentage of inside shell diameter,pertaining to core baffles of double-segmental baffles
Parallel or Transverse Cut of baffle edges with respect tonozzle axes
9
TUBE VIBRATION IN INDUSTRIAL SIZE TEST HEAT EXCHANGER(22 ADDITIONAL CONFIGURATIONS)
H. Halle, J. M. Chenoweth, and M. W. Wambsganss
ABSTRACT
Typical industrial shell-and-tube heat exchangerconfigurations are investigated systematically for the
occurrence of potentially damaging tube vibration as a function
of flowrate. In continuation of an ongoing experimental
program, results from shellside water flow tests of twenty-twoadditional test exchanger configurations are reported. The test
cases include single- and double-segmentally baffled tube
bundles having various combinations of triangular and square
tube layout patterns, baffle arrangements, and baffle edgeorientations. All layouts had a tube pitch-to-diameter ratio of
1.25. The testing focused on identification of the lowestcritical flowrates to initiate fluidelastic instability and/or
large amplitude tube motion and the location within the bundleof the tubes which first experience these responses. The
threshold flowrates are determined from a combination of methods
based on sensory observations, vibration amplitude data, and
frequency response information. Instability criteria are
preliminarily evaluated. Also reported are the measured overall
shellside pressure drop and the incremental pressure drops
across sections of the exchanger for all configurations.
I. INTRODUCTION
Tube vibration problems plague designers and operators of industrial
shell-and-tube heat exchangers. State-of-the-art computer programs can
optimize the thermal, hydraulic, and mechanical design, however
correspondingly advanced methods for evaluating flow-induced tube vibration
are not available. As a consequence, designers often face a dilemma between
overdesigning with increased capital and/or operating costs and risking
damaging tube vibration. Heat exchanger failures are costly. The actual
cost of repairing a vibration-damaged exchanger is usually far overshadowed
by the cost of interrupted production. Since many heat exchangers are used
by a wide variety of industries, the potential benefit to be derived from
improved tube vibration prediction methods is substantial.
A Heat Exchanger Tube Vibration Program was established at Argonne to
support the design of optimized, energy efficient, shell-and-tube heat
exchangers capable of operating without flow-induced vibration. As part of
this on-going program, tube vibrations are systematically being investigated
in a series of tests performed with an industrial-size test exchanger. Thisreport presents an update covering the most recently performed tests.
10
Besides the tests, the program includes the establishment of a databank of collected tube vibration field experiences and the utilization of
the data to contribute to improved current predictive methods and design
criteria. The Heat Exchanger Tube Vibration Program is sponsored by theU.S. Department of Energy (DOE), Office of Energy Utilization Research,
under the Energy Conversion and Utilization Technologies (ECUT) Program.
The tests experimentally investigate the effect of shellside water flow
on the dynamic behavior of the tube bundle. Tubes in a heat exchanger will
vibrate at virtually all flowrates to which they are exposed. At lowflowrates the response is of low amplitude and typically random in charac-
ter; a number of the closely spaced coupled modes are excited by turbulent
buffeting of the flow. These vibrations are generally acceptable; however,
consideration must be given to the potential for long term wear at the
tube/support interfaces. When the shellside flowrate is increased to exceed
a threshold value, fluidelastic instability occurs. This is an excitation
mechanism responsible for large amplitude vibration which, among other
things, can result in tube-to-tube impacting and cause rapid tube failure.
As such, it is the mechanism of most concern to designers and is the focus
for this testing program. Thus, the primary objective of the testing is to
determine the critical flowrate for the initiation fluidelastic instability
and to identify the location of the affected tubes within the bundle.
A test exchanger, representative of a segmentally baffled, industrial-
size, shell-and-tube heat exchanger has been designed and fabricated
specifically for this test program. The exchanger is shown in Fig. 1 as
installed in the Argonne National Laboratory's Flow Induced Vibration Test
Facility (FIVTF), and is described in a later section of this report. The
test work was initiated with tube bundles on a 300 triangular layout -
oriented with one side of the equilateral triangle perpendicular to the flow
direction - and with a pitch-to-diameter ratio of 1.25. The first test
report [1] covers five different test cases of eight-crosspass (seven
equally spaced baffles) bundles with different inlet/outlet nozzle diameters
for both full bundle and no-tubes-in-window (NTIW) configurations. A second
report [2] presents the results of tests with six-crosspass (five equally
spaced baffles) bundles, also on a 300 triangular layout with a 1.25 pitch-
to-diameter ratio. The ten reported test cases include a full tube bundle,
NTIW bundle, several proposed field fixes, and a bundle with finned tubes.
A third report [3] presents the results of eleven different test cases
having a 900 square tube layout with a pitch-to-diameter ratio of 1.25. The
test cases included various combinations of nozzle sizes, 8- and 6-crosspass
configurations, and full and NTIW bundles; in addition field and design
fixes and finned tubes were tested with a 6-crosspass configuration. A
preliminary evaluation of the instability thresholds and a comparison with
corresponding 300 layout configurations were presented.
This report presents the results of 22 additional test cases of various
layouts, all with a pitch-to-diameter ratio of 1.25. The test cases
11
Fig. 1. Test exchanger installed in Flow-Induced Vibration Test Facility.
ANL Neg. No. 113-79-100A.
Fig. 2. Test exchanger tube bundle in 900 square layout,7-crosspass configuration. ANL Neg. No. 113-84-51.
12
included 450 rotated square and 600 rotated triangular layouts with6-crosspass configurations, 300 triangular and 900 square layout 7-crosspass
configurations with different baffle cut orientations, 300 and 450 layout6-crosspass double-segmental baffled configurations with different baffle
arrangements and baffle cut orientations, and a special simulated U-tube
test.
In addition to the vibration testing, pressure drop measurements were
taken to contribute to the understanding of heat exchanger performance.
Measurements of the pressure drop overall and through various sections of
the test exchanger are presented for all test cases.
It should be noted that Heat Transfer Research, Inc. (HTRI), a not-for-profit research organization with over 175 members representing heat
exchanger designers, manufacturers, and users, is retained as a consultant
to the program. HTRI serves as an important two-way link with industry. It
provides the needed input relative to practical commercial designs, problems
experienced in the field, field and design fixes, and assists to transfer
the results of this test program to the industry.
Finally, for the sake of completeness and expediency, some of the
material on the background, test description, test procedure, etc.,
presented in previous reports [1-3] and particularly in paper [4] is
repeated here, updated and supplemented as appropriate.
II. BACKGROUND
A. General
At first glance a heat exchanger appears to be a relatively simple
mechanical structure, composed of a shell, tubes, and plates, and no
"moving" parts. However, the dynamic response of the tubes in an actual
unit is very complex. The complexities are associated with the tubes not
being perfectly straight, relatively small tube/baffle hole clearances, the
very large number of tube./'baffle interfaces, misalignment of baffles, and a
complicated, nonuniform flow pattern. These factors imply that at the many
tube/baffle interfaces the tube support condition may vary from one of
preload against the baffle to a floating condition in which the tube is
centered in the baffle hole. These conditions can be expected to vary with
operating conditions as the sheliside flow induces a drag force on the tubes
in the flow direction. Such changes in support conditions can be expected
to affect damping and, in some cases, frequencies and mode shape.
B. Vibration Response
The tests experimentally investigate the effect of shellside waterflow
on the dynamic behavior of the tube bundle. Tubes in a heat exchanger will
vibrate at virtually all flowrates to which they are exposed. At low
13
flowrates the response is of low amplitude and typically random in
character; a number of the closely spaced coupled modes are excited by
turbulent buffeting of the flow. At intermediate flowrates the tubes beginto "rattle" within the somewhat oversized holes in the intermediate support
baffles. Even though evidences of tube wear at the baffles have been
reported due to rattling, usually this has only caused failure after many
years of operation. It appears that the commercial heat exchanger industry
is not overly concerned about rattling as many exchangers operate quite
satisfactorily with it for many years. While field experience has shownthat these vibrations are generally tolerated, there is a need to understand
the potential for long term wear at the tube/baffle interfaces.
When the shellside flowrate is further increased, the amplitude of
certain groups of tubes g-ow to unacceptable levels. This increase in
amplitude may be gradual; however, it is more typical that once the flowratereaches a threshold value it triggers a fluidelastic instability. With only
a minor increase in flowrate, this excitation mechanism transforms previous
low level amplitude to large amplitude vibration which can result in rapid
tube wear either from tube-to-tube collisions or from tube-to-baffle
impacting. Fluidelastic instability has been shown to be the main cause of
tube damage. Consequently, it is the mechanism of most concern to designers
and is the focus for this program.
Fluidelastic instability with large amplitude motion involves a complex
fluid-structure interaction as the vibrating tubes alternately expand and
reduce the various flow paths within the bundle. The initiation of fluid-
elastic vibration is discussed by Chen [5]: when the flow velocity through a
tube array exceeds a threshold value, the fluid forces contributing to the
modal damping are such as to cause the damping to become negative and the
system to become unstable. The phenomena of fluidelastic instability can be
appreciated if it is realized that the narrow gaps between the tubes which
determine the flowpath are very sensitive to tube motion. For instance, in
a 1.25 pitch-to-diameter ratio layout, two adjacent tubes each closing in on
the gap between them with tube motions of only 5% of tube diameter reduce
the gap size by 40%. The earliest correlation for fluidelastic instability
was that developed by Connors [6], based upon experimental data using air
flowing across an idealized bank of tubes. Even though the general appli-
cability of Connors' method to actual heat exchangers is not established,
his method is currently used extensively and will be applied to obtain apreliminary evaluation of the current test data. For idealized conditions,
the nondimensional critical flow velocity UCR is characterized by
U- a CR- = 60.5
CR fDci
where UCR = critical flow velocity
14
f = tube vibration frequency
D = tube diameter
= instability threshold constant
and 6m = mv21c/pD2 , the mass-damping parameter
where, in turn,
my = virtual mass per unit length of tube
= equivalent viscous damping ratio
and p = fluid density.
For a particular tube bank, the tubes will be stable or unstable when the
actual crossflow velocity U is lower or higher, respectively, than the
critical flow velocity, UCR'
Chen [7] assembled available experimental data from a number of sources
and has plotted nondimensional critical velocity U as a function of the
mass-damping parameter am for each of the standard tubefield layout
patterns. He than identified lower bounds for the data and proposed a set
of stability diagrams. Other researcers, e.g. [8], have suggested still
other criteria and more can be expected in the future. In general, all willrequire a knowledge of the structural details of the exchanger, the flow
velocity, the damping, and the virtual mass of the tubes just as in Eq. 1.
Additional parameters may be required, such as the tube pitch-to-tube
diameter ratio, and the existing parameters may be "weighted" somewhat
differently.
Under localized flow conditions to be discussed in Section III.E,
vibration amplitudes were observed to rise generally with flowrate to
unacceptable levels prior to or without :. well defined threshold indicati ag
the "classic" fluidelastic instability. This indicates the need for
additional criteria when vibration must be considered to be a problem.
Even when a complete description of a heat exchanger is available, the
inherent imperfections of the actual hardware together with the many
components and interfaces results in unknowns such as the tube support
conditions, tube damping, and clearances that permit bypass flows. These
unknowns affect not only the structural, but also the flow characteristics.
The result of the tests indicate that, from a purely structural point
of view, the test exchanger tubes respond at frequencies reasonably close
the calculated modal frequencies. A better knowledge of the structural
damping (which may be also flow dependent) would be very desirable.However, at this time a definition and the determination of the
15
representative flow velocity appears to be the most promising approach to
improve the various prediction methods. This challenge is addressed in
Section III.C.2.
III. TEST DESCRIPTION
A. Test Exchanger and Flow Facility
The test exchanger is a segmentally baffled shell-and-tube exchanger,
representative of an industrial heat exchanger. It has a removable tube
bundle with component tubesheets, baffles, and tubes that are readilyrearranged or replaced to provide different test configurations. No heat is
transferred. There is no flow on the tubeside, 'he tube ends are open to
permit ready observation or instrumentation. The shell is piped to a large
water loop that is part of Argonne's Flow-Induced Vibration Test Facility(FIVTF) as shown in Fig. 1. Figure 2 shows the tube bundle on a specially
built transporter during assembly. The shell is seen in the background.
The general features, dimensions, and specifications of the test
exchanger are given on Tables 1 and 2. To facilitate comparison, additional
pertinent information is included.
During all but one of the tests reported herein, the test exchanger is
configured with 6 or 7 crosspasses, having 5 or 6 equally spaced baffles.
The baffles serve two functions: they determine the principal flow path and
provide support for the tubes. The regions where the baffles are cut to
permit the flow-turn-around are known as "windows." The tubes located in
the window regions lose the support of some of the baffles. Tubes having
the least support, have the higher number of the longest span lengths, the
lowest natural frequencies and thus the highest potential for vibration.
For the 6- and 7-crosspass configurations, the maximum unsupported tube
lengths of the plain test exchanger tubes are respectively 90 and77 percent, i.e., within the limit, of the maximum length recommended by the
TEMA standards [9] used by many industries.
Both nozzles are of the same nominal 14-inch diameter pipe size. The
inlet connection (left center of photo on Fig. 1) provides more than 12
diameters of straight pipe to reduce extraneous prior-to-entrance effects.
The nominal 10-inch size is provided by placing inserts (maintaining a long
approach) into both the inlet and outlet steel pipe. The central observa-
tion ports, built to serve as nozzles (and one of them was used as such
during one test) have windows that are contoured with transparent acrylic
plastic to provide a continuous surface at the internal shell diameter.
16
Table 1. General features and basic dimensions of test exchanger
Sheliside fluid
Tubeside
Shell (Stainless steel), I.D.
Shell, inside length (tubesheetspacing)
Mod'ila ;shell construction
Nozzles, inlet and outlet
Nozzles at shell midspan
Tube bundle
Tubesheets
Tie boits
Tie bars
W .Ler
No fluid, open tubes, ready insertionof instrumentation
0.59 m (23.25 in.)
3.58 m (140.75 in.)
Flexibility to change nozzleorientation
Insertion of piping to reduce insidediameter permits providing twonominal sizes/inside diameters
14-in. size/337 mm (13.25 in.) I.D.10-in. size/2'+1 mm (9.500 in.) I.D.
Observation ports or alternate flowroute
Removable unit, ready assembly/disassembly
One stationary, one floating; specialdouble tubesheet construction to con-tain 0-rings to seal tubes
Stainless steel rods in tube locationsSecure and space tubesheets on bothends of heat exchangerCompress double tubesheets on eachend to seal O-rings
Same O.D. as tubes
Secure and space baffle plates, 12.7 mm
(0.5 in.) overall O.D., eight locations,tied to outlet tubesheet
17
Table 2. Tube and tube bundle specifications
Tube, plain (Admiralty brass)0.D.Wall thickness
Tube layout patterns30 triangular
90* square
45 rotated square
19.1 mm (0.750 in.)1.2 mm (0.049 in.)
One side of equilateraltriangle normal to flow
Sides parallel and normalto flow
Sides oriented 450 to flow
600 triangular 60 , One side of equilateraltriangle parallel to flow
Pitch-to-diameter ratio 1.25
Number of crosspasses
Number of tubes (not counting 8 tie barsand, ti NTIW bundles, 4 tube positions inwindow regions)
30 triangular layout
90 square layout
450 rotated square layout
60* triangular layout
Outer tube limit (0.T.L.), maximumdiametral dimension of tube bundle
Baffle spacing
Baffle (brass)0.D.Thickness
8 (i.e., 7 baffles)7 (i.e., 6 baffles)6 (i.e., 5 baffles)
499, full tube bundle293, NTIW, 6 crosspass
421, full tube bundle245, NTLW, 6 crosspass
421, full tube bundle365, NTIW, 6 crosspass,
16% baffle cut
499,
425,
275,
full tube bundleNTIW, 6 crosspass,16% baffle cutNTIW, 6 crosspass,30% baffle cut
568 mm (22.374 in.), 30*and 60 layouts
562 mm (22.128 in.), 90*
and 45* layouts
448 mm (17.6 in.) approx.,8 crosspass
511 mm (20.1 in.) approx.,7 crosspass
597 mm (23.5 in.) approx.,6 crosspass
587 mm (23.109 in.)9.5 mm (0.375 in.)
Tube/baffle hole diametral clearance 0.4 mm (0.016 in.) minimum
18
B. Test Configurations
The principal features of the 22 different configurations, designated
Cases 27 through 48, tested are listed on Table 3. All tube bundles of this
test series had a number of common features: plain tubes of the same size
and length, spacing with a pitch-to-diameter ratio of 1.25, and insertion in
the same shell. Refer to specifications in Tables 1 and 2.
Test cases 27-29 investigate tube bundles with 450 rotated square and
test cases 30-34 bundles with 600 rotated triangular tube layout patterns,
all with six crosspasses. Test cases 35-38 cover tube bundles having 300
triangular and 900 square layout bundles with 7 crosspasses. While the
above and all previously tested tube bundles had single segmental baffles,
cases 39-47 investigate the performance of bundles having double-segmental
baffles with 300 and 45* layouts and with various baffle arrangements.
Case 48 is a special test to simulate a U-tube heat exchanger. One of thetest parameters investigated during this series of tests was the effect of
the orientation of the baffle edges with respect to the nozzles. This
feature requires some initial discussion and clarification. The configura-
tions tested under this program had baffle edges oriented either transverse
or parallel to the nozzle axes. In short this feature will be referred to
as transverse or parallel cut baffles. It is noted that the terms
"horizontal" and "vertical" baffle cut have been used by the industry for
transverse and parallel cut, respectively. However since this conventionaldefinition is based on vertical nozzle axes and test setup had horizontal
nozzle axes, the "horizontal," i.e., transverse baffle cut was actually
oriented vertical and vice versa. The use of the terms transverse and
parallel baffle cut avoids any confusion.
C. Test Parameters/Instrumentation/Data Processing
1. Acceleration and displacem' ct
It is practically impossible to instrument all of the more than 400
tubes in the bundle, or even the somewhat smaller number in the window
regions that are more susceptible to vibration by virtue of their lower
natural frequencies. Limited by the available instrumentation and tape
recording channels, four to eight tubes are selected to be instrumented with
miniature accelerometers, on the basis of exploratory tests. The
accelerometers are mounted on specially designed plugs and are inserted into
the tubes. Since experience indicated that with few exceptions, to be
discussed in later sections, the tubes vibrated at the lowest natural
frequency corresponding to the first bending mode, the accelerometers were
usually positioned at or near the center of the larger tube spans with
double-baffle-spacing length.
In almost all cases the accelerometers were oriented to be
sensitive in the lift, i.e., transverse-to-flow, direction. This was done
because it appears that tubes usually initiate impacting upon instability by
19
Table 3. Test cases and configuration code
Configuration Code
Identification of TubeBaffle Cut Row or Number
Tube --- locatedBundle Orien-Full tation nearest to, saddledNTIW Number Nom. Trans- farthest inDouble Add. of Nozzle verse or from baffle
Case Seg. Info. Cross- Size Tube % Parallel nozzle on top, edgesNo. U tube * passes in. Layout ** Cut *** bottom t
27 F " P * 6 * 14" * 450." 16% TC A,GG 1,33 CC,E
28 N " P " b * 14" * 450 * 16% TC E,CC 1,33 CC,E
29 F " P " 6 " 14" " 45 *" 30% TC A,GG 1,33 X,J
30 F " P * 6 * 14" * 600 * 16% TC A,UU 1,27 00,G31 N * P * 6 * 14" * 60* 0 16% TC G,00 1,27 00,G
32 F " P " 6 * 14" * 60 *" 30% TC A,UU 1,27 HH,N33 F * P " 6 * 14" * 60*0. 30% PC 27,1 A,UU HH,N
34 N " P " 6 * 14" * 60 " 30% TC N,HH 1,27 HH,N
35 F * P " 7 * 10" * 30* " 29% TC A,AA 1,47 T,N
36 F " P e 7 e 10" 30 * 29% PC 1,47 AA,A T,H
37 F " P " 7 " 10," 90 " 30% TC A,W 1,23 Q,G
38 F " P " 7 * 10" * 90 * 30% PC 1,23 W,A Q,G
39 D " C " 6 " 10" - 300 * 25% PC 1,47 AA,A G/U,I/S
40 D " C " 6 * 10" * 30 *" 25% TC A,AA 1,47 G/U,I/S41 D " W " 6 " 10" " 30 * 25% TC A,AA 1,47 1/S,G/U42 D " W " 6 " 10" " 300 * 25% PC 1,47 AA,A 1/S,G/U43 D " C * 6 * 10" * 45 * 27% PC 1,33 GG,A I/Y,K/W
44 D " C 6 * 14" * 45 * 27% PC 1,33 GG,A I/Y,K/W45 D " C e 6 * 10" e 450 * 27% TC A,GG 1,33 I/Y,K/W
46 D " W " 6 * 10" * 450 * 27% TC A,GG 1,33 K/W,I/Y
47 D " W " 6 " 10" " 450 * 27% PC 1,33 GG,A K/WI/Y
48 U " P " 4 " 10" " 300* 29% TC A,AA 1,47 T,H
* P - Plain tubesC - 3 core and 2 wing bafflesW - 3 wing and 2 core baffles in double-segmental baffled tube bundles, plain tubes
** Baffle cut as percentage of inside shell diameter (to 2 significant figures).For double-segmental baffles: pertaining to core baffles
*** In NTIW bundles, four of eleven tie bolts are located outside of tube bundle as indicatedon schematics.
t Letters in front of comma pertain to first baffle window(s) from inlet.
20
large out-of-phase vibration in that direction. However, a biaxial set-upwas used for one of the most susceptible tubes.
The data processing of tape-recorded signals generated by the tube-
mounted accelerometers makes extensive use of a sophisticated Fast Fourier
Transform Analyzer. This is essentially a specialized mini-computer supple-
mented by a graphics package to allow the preparation of hard copies. The
signals are used to obtain and plot acceleration and (by double integration)
displacement power spectral density curves and the corresponding integrals.
The area under these integrals determines the root mean square value of the
acceleration or displacement within the bandwidth considered.
2. Water flowrate and crossflow velocity
The crossflow velocity is one of the most significant parameters
influencing the vibration performance of heat exchanger tubes. In
laboratory tests with uniform crossflow, most researchers consider the mean
crossflow velocity in the gap between non-vibrating tubes to be "the"
characteristic flow velocity; this velotr" can be easily calculated in such
situations. However, in a real heat exchanger the complex flow patterns and
nonuniform axial distribution makes the determination of a characteristic
crossflow ve Ecity a challenge. Obviously, a single value for crossflow isnot sufficient to predict instability when different groupings of tubes
undergo instability at different flowrates. Experimental determinationpresents difficulties considered beyond the scope of the present program as
discussed in Reference [1]. An effort to determine the local flow veloci-
ties by means of flow distribution computer programs has been reported
[10-12]. These programs have the potential of calculating not only thevelocity in the pure crossflow regions but also in the window f low-turn-
arounds, where the tubes most susceptible to instability are located.
For the present analysis, the crossflow velocity can only be
determined by computation from the water flowrate through the test
exchanger. The flowrate is measured in the upstream piping with turbine
flowmeters, whose signal pulses are recorded to facilitate the subsequent
data analysis. For the evaluation of the tests in this study, the HTRI
Computer Program ST-4 [13] based on the Stream Analysis Method [14] was
employed for the calculation of the crossflow velocity from the measured
flowrates. This velocity is the integral average of the maximum velocity
occurring in the minimum tube gaps of the tube bundle. Taking a "global"
approach, the calculation takes into account the flow diverted from the tube
gaps due to leakage through various bypass paths, around the tube bundle,
through tube/baffle holes, and around baffle/shell clearances. The extent
of these leakage flows depends upon the pressure drop across various
internal sections of the heat exchanger.
Tests indicate that different groups of tubes underwent instability
at different flowrates and that different flow conditions were involved.
Thus, to assess the vibration potential of a particular configuration more
21
accurately, the dynamic response of individual tubes needed to be
evaluated. Investigations have shown that the determination of an"effective" crossflow velocity Un requires consideration of two
parameters. The first is the axial distribution of the crossflow velocity
U(z), a function of axial distance z along the entire length R of the tubewhich can be obtained from a three-dimensional computer model that
numerically simulates the shellside flow distribution. The second parameter
is the mode shape *n(z), i.e., amplitude versus length, of the mode n with
which the tube is considered vibrating. The mode shape n(z) and the
corresponding vibration frequency are obtained by means of a modal analysiscomputer program. The combined reinforcing effect of the axial velocity
distribution and mode shape determines an effective (or equivalent uniform)
crossflow velocity used by many investigators [5,15] and defined as
R2 2 1/2f U2(z) (z)dz
Un= 0 (2)
J *2 (z)dz0
The effect is reinforcing in the sense that a good "match" between the flowdistribution and the mode shape anywhere along the length of the tube
contributes significantly to the value of the effective crossflow veloc-
ity. Subsequently the reduced effective crossflow velocity, U = Un/f D,
is evaluated for each mode. The mode resulting in the highest value of Unis the one most likely to vibrate. As will be further discussed, this ismost often the first or second mode, but there are important exceptions.
Computer programs have the potential to calculate not only the velocity inthe purely crossf low regions of a tube bundle, but also in the baffle windowflow-arounds, or wherever tubes may be most susceptible to vibrate. Then,
together with the calculated value of the the mass damping parameter am the
potential for instability can be evaluated by whatever criterion is selected(a threshold instability constant 8 or a stability diagram). Chen [5] has
shown Eq. (2) to be valid for high values of mass-damping parameter (gas
flows). However, the full validity of Eq. (2) as an approximation is
subject to question when low values of mass-damping parameter, i.e., liquid
flows, are involved.
"Global" computer programs are available, and are easy and
inexpensive to run. They are effective in designing and evaluating the
thermal/hydraulic performance of heat exchangers and, when coupled with a
suitable vibration analysis, well suited to screen out obvious vibration
problems. However, it should be pointed out that their very success in
optimizing heat exchanger performance (often by utilizing much higher
shellside velocities) has brought tube vibration problems into the
foreground.
22
The application of a three-dimensional flow distribution computerprogram, combined with the modal analysis, would greatly assist the
vibration prediction methods and efforts are underway to develop these
sophisticated programs to a point where they can be universally applied
[12].
3. Other
The pressure drop across the entire exchanger as well as throughvarious internal sections was measured and reported in Section VI. The
corresponding pressure drop data measured during previous tests are reportedin Refs. 16 and/or 17. The generated data are expected to be useful for the
improvement of computer programs for industrial heat exchanger design as
discussed above.
The flow tests were performed with isothermal water at room
temperature. A time code signal was recorded simultaneously with the
acceleration and flowmeter signals. The subsequent data analysis was
greatly facilitated by the capability of the time code generator/translatorunit to read and display the recorded time of any event such as instability
initiation.
D. Test Procedure
The test procedure is to investigate the vibration response of the tube
bundle as a function of flowrati. Of primary interest is the determination
of the critical flowrate, which is the lowest flowrate initiating insta-
bility or other unacceptable response and the identification of the tubes
involved. However, whenever possible, higher flowrates are tested to study
additional large amplitudes or vibration responses in other locations of the
bundle.
The testing of any particular configuration was typically initiated
with an exploratory waterflow test to examine the overall dynamic behavior
of the tube bundle by means of sensory observations using eye, ear, and/or
finger touch. In the basis of vibration response, the tubes considered most
essential for the investigation of the bundle were provided withaccelerometer instrumentation. The subsequent tests were performed in two
ways: (1) a constant flowrate was established and the instrumentationsignals were recorded for a time sufficient to average a number (usually 10)
of samples for frequency and spectrum analysis and (2) the flowrate was
varied (scanned) through a range to record changes in the vibration
response, and, in particular, to determine the flowrate at the initiation
and termination of the fluidelastic instability.
At low water flowrates, turbulent buffeting vibrated the tubes with
very small magnitudes that increased moderately with flow. At intermediateflowrates, and as the flowrate was increased, rattling of the tubes within
their baffle supports was heard and detected on accelerometer signals.
23
There was no visual evidence of more than a slight quiver in the tubes,
sometimes seen only as the bouncing of small dust particles in the
backlighted bores. Occasionally, the rattling would temporarily cease as
increasing flow and changing pressure forces "seated" tubes. As the flow
was increased further, a critical flowrate resulting in large amplitude
vibration was reached. Most of the previous tests performed under this
program, and some of the presently reported tests, incurred fluidelasticinstability under "classic" conditions as discussed in detail in the
following section. In those cases the initiation of fluidelastic
instability was characterized by a large increase in amplitude with a small
incremental increase of the flowrate. The onset of instability was easilydetected by the abrupt changes of the accelerometer signals and by a sudden
increase in audible noise from the unit. There were occasions when duringtesting with a "constant" flowrate some transient or perturbation was
apparently sufficient to trigger the process.
E. Critical Flow Conditions
As the test program proceeded, it became evident that undesirable
vibration could also be generated by flow conditions other than the
crossflow that initiates "classic" fluidelastic instability in the interiorof the bundle. These flows are either the entrance and exit flows into and
out from the tube bundle, or the localized high velocity bypass and shortcutflows. To facilitate discussion, these three conditions will be treated
separately, even though they are interacting and the flow-induced vibration
mechanisms may not be clearly distinguishable.
Classic Fluidelastic Instability
An instability is considered to be "classic" if its behavior approaches
that of the well-researched fluidelastic instability, even though the flow
and structural conditions in the test exchanger are far from uniform and
ideal. This instability is initiated by a complex fluid-structure
interaction as the vibrating tubes periodically change the gap, and
consequently the flow path between them. Applied to this study, the
"classic" instabilities have the following characteristics:
a. A group of tubes located in the interior of the uniformly patterned
tube bundle are exposed to similar flow conditions.
b. The tubes are approached with strong crossflow velocities emergingfrom the space between adjacent baffles. It is noted that the tubes
going unstable are within two rows of the baffle edge and are
immersed in a flow region that has considerable axial 21.-,w
components as the crossflow direction reverses. Certainly these arefar different from the ideal uniform crossflow velocity conditions
used in laboratory tests and assumed in most analytical models.
24
c. Although the velocity distribution is varying along each tube, flow
excitation presumably occurs along the entire length.
d. For the relatively narrow tube pitch-to-diameter ratio of 1.25,fluidelastic instability is triggered when the flow exceeds a
threshold value for plain tubes with 300, 600, and 90* layout
patterns. A small additional increase in flow causes a largeincrease in vibration amplitude often resulting in tube-to-tube
collisions as adjacent tubes vibrate out-of-phase in the transverse-
to-flow direction.
On the other hand, bundles with plain tubes in a 450 layout,
demonstrate a more gradual rise in amplitude before a not-so-well
defined instability threshold is reached. Finned tube bundles with
300 and 900 layouts and an effective tube pitch-to-diameter ratio of
1.41, show a similar complex behavior.
e. Almost always the vibration occurs at the lowest (fundamental)
natural frequency.
f. Further increase of the flow typically causes additional tubes to
vibrate, but never results in a decreased vibration level.
g. Usually the flow has to be reduced below the initiation threshold in
order to stop the vibration. At times this hysteresis amounts to
more than 20 percent.
Entrance and Exit End Zone Flow Vibrations
Heat exchanger designers must be concerned about vibration and erosion
protection for tubes exposed to the flow as it enters the tube bundle from
the inlet nozzle. TEMA [9] recommends impingement protection whenever the
pV2 of the entering flow exceeds 2230 kg/m s2 (1500 lb/ft sec2). Depending
upon the bundle entrance configuration, a portion of the flow bypasses the
tube bundle through the clearances between the bundle and the shell.
Further, the mean tube gap velocity may be smaller, but typically is larger,
than tie initial approach velocity in the nozzle.
The flow-induced tube vibration excited by the entrance and exit flows
were sometimes observed in these tests. In contrast with the "classic"
instability, these flows demonstrated the flowing characteristics:
a. Tube vibration is excited by flow in the end zones of the exchanger
where typically the bundle has one of its shorter spans. The
frequency that is excited is usually one of the higher modes whose
mode shape has a relatively larger amplitude in the exposed span.
25
b. While severe high frequency vibration could be generated in tuberows immediately under the inlet nozzle, for transverse-cut,
segmental baffled bundles, this generally occurs at flowrates above
the threshold for the "classic" instability in the interior of the
bundle.
c. Vibration amplitude usually rises gradually with flowrate.
Leakage and Bypass Flow Vibration
The tests indicate that isolated tubes or small groups of tubes located
at or near the periphery of the tube bundle can be excited into large
amplitude vibration and instability. The apparent causes are the high
velocity flows from short cuts, bypasses, and leakages. Typically, theseare long-span tubes located in the "corner" regions of the baffle windows
where the baffle edge meets the shell. Such excitation is particularlyprominent in the "corner" region in the first baffle window nearest the
nozzle for tube bundles with parallel-to-nozzle axes cut baffles as the flow
shortcuts into the second baffle space. Another example is the flow
bypassing the tube bundle through the clearances between the bundle and the
shell. The skimming instability investigated by Connors [18] fits into this
category. Unless interacting or overtaken by a "classic" instability, the
typical characteristics of the leakage and bypass flow vibration are the
following:
a. Only a few tubes on or near the periphery of the bundle are
involved.
b. Vibration amplitudes rise (and fall) gradually with flowrate and may
reach tube-to-tube collision levels. Tubes usually vibrate at theirlowest natural frequency.
c. Flow excitation is probably most prominent in or near the end zones,
even though it could occur at intermediate positions of the tube
length.
F. Vibration Response Criteria
The second of the subject program's test reports [2] presented an
extensive discussion of the background information, divided into the main
topics of "instability mechanisms" and "criteria for determining critical
flow." The latter lists five criteria: sensory observations, vibration
amplitude vs. flow-response rate, vibration amplitude vs. flow-amplitude
threshold, flow sweep-time history, and frequency response data. As dis-
cussed in Ref. 2, each of the five criteria has advantages and disadvantages
relative to another. In the analysis and interpretation of data from the
subject tests, all five methods are employed to various degrees. However, a
heavier reliance is placed on time histories from flow sweeps and
26
examination of the rate of increase of vibration response with flowrate
(vibration amplitude vs. flow-response rate criterion) to identify the
increase in response which characterizes the onset of instability. The
reader is referred to the detailed presentation in the "background" chapter
of Reference 2.
Section III.E discusses three critical flow conditions causingundesirable vibration response. For this series of tests the task of
determining the critical flowrate became more difficult than it had been for
previous tests where a usually abrupt increase in amplitude with flowrate
and subsequent tube-to-tube impacting led to a ready identification of a
classic instability threshold. This is particularly the case for the 450
rotated square layout tube bundles as well as for some other configurations
having tubes exposed to locally high velocities. These tube bundles
responded with fluidelastic instabilities, but the corresponding initiation
thresholds, if determinable, do not necessarily constitute the critical
conditions of unacceptable tube bundle performance. This is because the
tube vibration amplitudes increased more or less gradually with flowrate,
with often only subtle instability-related phenomena such as frequency
spectra peaks, an amplitude versus flowrate peak, or frequency shifts on the
way to tube-to-tube impacting levels. Sometimes no such events were
encountered until impacting. However, somewhere on the way up, the
amplitudes reached a threshold, yet to be defined, where the tube vibrationresponse appeared to become unacceptable based on engineering judgment.
This occurred at flowrates when the tubes vibrated vigorously in the baffleholes even though tube-to-tube collisions could not be verified (and may
indeed have not occurred) and before any abrupt-with-f lowrate instability
could be observed.
There is a need to define the threshold of unacceptable tube bundle
performance. Two separate criteria may be considered. One is the onset of
fluidelastic instability identified on the basis of the sharpening of the
frequency response peak on the power spectral density curve. This criterion
may be satisfactory when the response does not show any abrupt-with-flowrate
increase. The second criterion is the onset of tube damage. Permissible
operation of the heat exchanger without tube failure may allow a higher
flowrate than the first criterion. The second criterion could be based on
vibration response limits in terms of tube displacement, velocity, or
acceleration to define the flowrate at which the response of the bundle is
considered to become unacceptable. For instance, displacement could define
bending stresses, acceleration could relate to collision and wear damage,
while a structural velocity criterion would provide a measure of momentum
change. However, even if such criteria had been available, the
determination of the permissible performance would still be restricted by
the limited number of tubes (not to mention axial locations and radial
orientations) that can be practically monitored with instrumentation.
27
IV. FLOW TESTS
The flow tests were performed following the test procedure outlined in
Section III.D. To facilitate reporting of the results, the 22 cases were
divided into groups. This section presents descriptive case histories as
well as tabular summaries on two types of tables that respectively present
(1) the flowrate and locations of various vibration phenomena observes, and
(2) the critical flow parameters of the one or two most critical phenomena
with computer-determined mean-gap flow velocities and a preliminary
comparative evaluation of the instability threshold parameters as described
in Section V. Sensory (sight, sound, feel) observations for each of the
test cases are documented in the Appendix.
A. 450 and 600 Layout, 6-Crosspass Configurations (Cases 27-34)
All previous tests under this program had been performed with 300triangular and 900 square tube layout patterns [1-4]. The purpose of the
450 rotated square (Cases 27-29) and 600 rotated triangular (Cases 30-34)
layout, single-segmental baffle configuration was to provide a comparison
with the earlier test results, since all four layouts are employed in
industrial heat exchangers.
The 450 and 600 layouts were obtained by rotation of identical
respective 900 and 300 patterns previously tested. Thus the same tubesheets could be used, but new baffles had to be fabricated to provide
properly oriented baffle edges. To investigate the effect of baffle cut,
Cases 27, 28, 30, and 31 were equipped with a 16% and Cases 29, 32, 33, and
34 with a 30% baffle cut, i.e., the opening of the flow-turnaround window
expressed as a percentage of shell inside diameter. Cases 27 through 32 and
34 had the baffle edges oriented transverse to the nozzle axes, as had been
the case for all previous tests. Case 33 was the first configuration tested
with a parallel-to-nozzle axis baffle edge orientation.
Cases 28, 31, and 34 are no-tubes-in-window (NTIW) configurations.
Heat exchanger designers resort to th.s somewhat drastic step of foregoing
heat transfer capacity in the window regions to ensure against a vibration
problem. Because the absence of tubes in the windows permits full
utilization of the window area for the flow and because one endeavors to
omit only a minimum amount of tubes to provide the NTIW configuration, the
baffle cut for an NTIW bundle is usually reduced compared to the cut of afull tube bundle. Thus the aforementioned small and large baffle cuts are
fairly conventional for NTIW and full bundles, respectively. For the test
exchanger the NTIW configurations were obtained by removing all (but not the"saddled") tubes in both window regions. The unused baffle holes were
covered and the tubesheet holes plugged and sealed.
A diagram of the test exchanger in a typical 6-crosspass configurationwith transverse baff!' cut orientation is shown on Fig. 3. Schematics of
various 45* and 600 layouts are presented on Fig. 4. The mre detailed test
28
3.58 m (140.75 in.) TUBE LENGTH INSIDE SHEL L
3 SPAN TUBEBAFFLE--OBSERVATIONBAFFLEPORT (TYP.)SPACING FAR 6 SPAN TUBE
WINDOW"
A== = 4f I
U
HI
7 ti II 1'0o ti- I-. ..
/ II
4 SPAN TUBE
UI
HI
OUTLET
NEARWINDOW"
INLET
-0.59 m (23.25in.) SHELLINSIDE DIAMETER
Fig. 3. Test exchanger in 6 crosspass/5 baffle configuration
pat 1Fqmr--
1
T 1rT li
-
w
29
"o0o O "FAR" "NEAR""O-?.S0
0 0J0 0 00 000 0 0BAFFLE {ogo7,oco00 00 o7___ CO0O0 0000 000WINDOW 'ooooOOOOO0 &oo
)-OQQO0()0 0 O - oU 000000CD000000 3 on0oo0000~00D"?00'Oo00c/.o' oo ooooo 000c~~&_GDC(+0 0000 0O O O O C 000000000occ '00
O '00o'0O * 0000 ODOO( ) . "00000C 0. 9 00 OH &0 000"O 0000000 0000O OOC 0000000. 00( no 00000oacca00 oooC00000000 O~CYO _.0 00000FLOW ~ooccc. ooc F LOW 000000000 ,ooooooo
00,0 _'_~Cv000' O OU .t._ 0000!0 0000Th 00 O 0000 0OOO0 000 /00'_'.UL : 000 1O.X rOC O'_O O .C0000NOZZL _J0>o ~0~0000 $0' 0;O00
"INLET L Cl0 0~," INLET "00 000 0 0 00 .INLET $0D GNOZZLEc000 0000O0 .''0 000) 0000O!o~o 0000C00000v
CO0C r0000001/0 00000000 00000b0or00 -"(\00000000,00\D,
0' 000
0 0 ,OK 00000 O,
Case 28N"P"6'14" .450 "16%TC
0 000000000000
00 0 0000COO00INLET 0 0000)00000000000
*0000000000000000000000000000000&OcoOOOoQ00000000000000
00 0('ooO) 00000
Case 3000 00000FP6 '14" .600 *16%TC0
* O0000000000 OFLOW o 0( 00000000 000 oc 000 0000
00 000000000000 0000 000 0000010000O e
000000( 00000: (Q( 00000000C 000000000000 00
00E OO00000 )0000( 0(00000OQOOC0C C '00( 00000 000
000LE 0000000000 000000000000000000 0000
000 0000000 00000000000 0 00000000
COQO 00000000" 0000
INET00000 0000000000 00000NOZZLE 00 0 00000000 00000e
00 00 0000000000.OGO 000000.0 00
FP60 '14"0.00*30000
Case 29F"P"6.14" "45 "30%TC
* '00000000-000000000 000
00000_.000 00000000000000000000
0000'> oOooO00oO00000000000000
o000'0000000000OOOoOOOO0(;OOOOOO0000000000000000QO0000'G? 00000000( ,0000000000000000000000UC00000000000
0000D. 000000) '000000 000000000000
INLET 00000000000000ONOZZLE 00 000000000000000 0.
00000000000000QQQQ('00c00000000OQ )0( 00000000
Case 31N"P"614" .60 "16%TC
000000" .00 *00P
Fig. 4. Schematics of typical 450 and 600 test configurations
30
results for the 450 and 600 tests are presented in Tables 4 and 5,
respectively; comparative data are listed on Table 6.
Case 27
Case 27 is a 6-crosspass full tube bundle configuration with a 450rotated square layout pattern, 14 in. inlet/outlet nozzles and a 15.5%
baffle cut. For full tube bundles this baffle cut is smaller than is
conventional for industrial practice, since the small window areas promote
relatively large window flow velocities and large overall pressure drops.
The small baffle cut was selected because 1) it is typical for the no-tubes-
in-window bundle to be tested subsequently (Case 28) and 2) it will provide
a comparison with a following full bundle test with a larger baffle cut
(Case 29).
Upon testing, as the flowrates were increased, the subject tube bundleindicated that the tubes near the shell periphery in both window regions
vibrated sooner and more vigorously than those in the central region.
However, it was in the central region next to the baffle edge in the far
window (opposite the nozzles), where a fluidelastic instability with
impacting initiated at 0.172 m3/s (2720 gal/min). Further increase to the
highest flowrate of 0.190 m3/s (3010 gal/min) applied caused almost all farwindow tubes to vibrate very actively if not to impact. The instrumentation
indicated that the tube vibration in the far window occurred principally at
frequencies associated with the second and/or third mode. Upon flow
reduction, the impacting ceased at about 0.162 m3/s (2560 gal/min).
Tube-to-tube impacting of the tubes in the near window may have
occurred at the highest flowrate tested but could not be verified. From
sensory observation it appeared that a part of the flow bypasses the central
core of the bundle not only by leakage between the bundle and the interior
surface of shell but also leaks through the first and second tube gaps from
the bundle exterior where these present in-line orientation, reduced
resistance flow paths. Post test examination upon disassembly revealed that
some of the tie bar sections spacing the baffle plates had buckled. This
condition was apparently caused at the maximum flowrates by the highpressure drop between adjacent baffle spaces. The situation was aggravated
by baffles blocking about 90% of the shell cross section and tie bars placedinto compression. This pressure drop applied was much higher than
conventional in industrial practice.
Case 28
Case 28 is a 45* rotated square layout, 6-crosspass, 14-inch nozzle,
15.5% baffle cut, no-tubes-in-window configuration obtained by removing all
tubes in both windows in rows A through D and DD through GG from the Case 27
bundle. Tested up to 0.227 m3/s (3600 gal/min), the sensory observations at
the higher flowrates indicated severe vibration of the tubes in the baffle
holes, particularly in the first rows exposed to the nozzle inlet flow.
31
Table 4. Flowrates associated with instability and tube impacting or withlarge vibration amplitudes at different locations in tube bundle.Cases 27 to 29
450 rotated square layout, 6-crosspasses,
Flowrates in gal/min (1 gal/min = 6.309
27Full
CaseBundle TypeBaffle Cut
Orientation15.5
Transverse
14-in. nozzles.
x 10-5 m3/s)
28NTIW
29Full
15.5 29.8Transverse Transverse
Location and Instability phenomenon
Far window, central region,near baffle edge
Frequency response peak
Amplitude vs. flowrate peakVibration activity oramplitude increase
Impacting initiatesImpacting ceases
Near window, most tubesImpacting possiblebut not verified
Core region, central regionof rows exposed to nozzle
Frequency response peak
* Identified as the lowest critical flowrate
10001400
*27202560
1970*2140 est.
3010
3000*
32
Table 5. Flowrates associated with instability and tube impacting or withlarge vibration amplitudes at different locations in tube bundle.Cases 30 to 34
600 rotated triangular layout, 6-crosspasses, 14-in. nozzles.
Flowrates in gal/min (1 gal/min = 6.309 x 10-5 m3/s)
Case 30 31 32 33 34Bundle Type Full NTIW Full Full NTIWBaffle Cut
% 15.5 15.5 29.6 29.6 29.6Orientation Trans- Trans- Trans- Parallel Trans-
verse verse verse verse
Location and Instability phenomenon
Far window, central region,near baffle edge
Impacting initiates 2370 1840Impacting ceases 2230 1330
Far or first window, baffle edge-shell "corner"
Impacting Top Bottom NearInitiates 2470 2910 1590*Ceases 1650 2700 1430
Near window, near baffle edge,central regionImpacting initiates 2430 3270Impacting ceases 2250
Tubes under nozzleFrequency response peak 3270
Core regionNo significant vibration 2990Vibration activity may beunacceptable 3370
Considered unacceptable 2880
* Identified as the lowest critical flowrate
33
Table 6. Critical flow parameters of 450 and 60 layout, 6-crosspass test exchanger configurations
*Lowest TypicalCritical or Experimentalttnstability Computed and InstabilityThreshold Gap Flow Theoretical Reduced*,, Threshold
Case ** Flowrate Velocity,U Frequency,f Velocity ConstantNo. Configuration Code Location m3/s gal/min m/s ft/s Hz U g
27 F.P.6.14"445* 16%TC FBE 0.172 2720O 1.29 4.22 38.6 Ex 1.75 2.2127.3 Ex 2.47 3.1323.5 Th 2.87 3.63
28 N.P.6.14""45*.16%TC NBE 0.189 3000 1.36 4.47 71.0 Ex 1.0179.1 Th 0.90
29 F.P.6.14""45*.30%TC FBE 0.124 1970 1.03 3.38 22.5 Ex 2.40 3.04t 23.5 Th 2.30 2.91
FBE 0.135 2140 1.11 3.65 24.0 Ex 2.43 3.0823.5 Th 2.49 3.14
30 F.P.6.14""60*.16%TC FBE 0.150 2370 1.23 4.04 23.5 Ex 2.75 3.3922.9 Th 2.82 3.47
NBE 0.153 2430 1.26 4.14 25.5 Ex 2.60 3.2023.8 Th 2.78 3.43
31 N.P.6.14".60*e16%TC FBE 0.213 3370 1.77 5.80 70 Est 1.3377.2 Th 1.20
32 F.P.6.14".60*.30%TC FBE 0.116 1840 1.08 3.55 17.5 Ex 3.25 4.0022.9 Th 2.48 3.06
33 F.P.6.14".60*%30%PC FCR 0.100 1590 0.89 2.91 19.0 Ex 2.45 3.0222.9 Th 2.03 2.50
34 N.P.6.14""60*%30%TC C 0.182 2880 1.54 5.04 70 Est 1.1577.2 Th 1.04
* Lowest critical flowratet Flowrate of threshold initiating "classic" fluidelastic instability
** Location code: C - center, F - far or first window, N - near windowFollowing letters: BE - next to baffle edge, CR - corner region nearest nozzle
*** - U/fD; D - 19.1 mm (0.75 in.)
34
Even though the tubes are supported with spans too short to permit tube-to-tube impacting, there appeared to be some fluidelastic instability. For
further investigation selected tubes were instrumented and another test
performed. The analysis of the data indicated that an instability initiatedin the central tubes in the rows exposed to the nozzle at a flowrate of
about 0.189 m3/s (3000 gal/min) as evidenced by a "sharpening" of the
frequency response peak at about 70 Hz on the power spectral density plots.
Case 29
Case 29 is a 6-crosspass, full bundle, 450 layout configuration with an
increased 29.8% baffle cut obtained by trimming the baffles accordingly.
Initially, the following discussion will focus on the central tubes in the
rows next to the baffle cut in the far window opposite the inlet/outlet
nozzles. As had occurred in the previously tested full tube bundle
configurations with 300 triangular and 900 square tube layout patterns, the
fluidelastic instability initiated in this region also for the subject tests
with a 450 rotated square pattern. The initiation of instability at a
flowrate of 0.124 m3/s (1970 gal/min) was sensed as a severe vibration, but
not accompanied by as dramatic a rise in amplitudes as had been observed in
the earlier tests. Compared to the latter, the data from three tubes
instrumented with accelerometers indicated two differences in performance.
First, prior to the initiation of instability, the subject tests resulted in
sharp frequency response spectra at flowrates as low as 0.063 m3/s
(1000 gal/min), moderate peak-to-peak amplitudes rising to about 6% of tube
diameter at 0.053 m3/s (1400 gal/min), and a subsequent reduction producing
a dip of the amplitude versus flowrate curve at about 0.101 m3/s
(1600 gal/min). Secondly, upon instability, the tube vibration amplitudeswere not sufficiently large to indicate tube-to-tube impacting, even though
the accelerometers were at the locations optimum for sensing first mode
vibrations corresponding to the frequencies measured, about 22-24 Hz. For
instance, a biaxially instrumented tube indicated a peak-to-peak amplitude
to diameter ratio of about 10% in the 450 direction, short of the
theoretically 25% required for tube contact in a 1.25 pitch-to-diameter
ratio tube bank. Even though tube-to-tube collisions could not be verified,
the vibration impacting in the baffle holes was sufficiently severe to
rotate and axially move the tubes in the 0-ring seals. Because of concern
due to escalating vibration activity including tube-to-tube impacting
estimated to have initiated at 0.135 m3/s (2140 gal/min), flow beyond
0.170 m3/s (2700 gal/min) was not applied. Up to that flowrate the region
of instability in the far window increased, but did not extent to the bottom
shell periphery tubes.
As far as the near window region is concerned, an instrumented tube in
the front row directly exposed to the inlet nozzle flow indicated at the
highest flowrates a tuned frequency response atid possible fluidelasticinstability. The vibration frequencies were about 75 Hz, corresponding to
the third or fourth mode. The measured vibration amplitudes were small.
35
As indicated below, the occurrence of the maximum mean gap velocities
at angles (i.e., 450) to the principal flow direction is considered to be a
contributing factor to the differences in vibration and pressure drop
performance compared to the 300 and 900 layout bundles.
Visual observations indicated that a fair part of the flow bypasses the
central core of the 450 bundle not only by leakage between the bundle and
the shell but also by short-cuts through the first and second tube gaps from
the bundle exterior where these present reduced resistance flow paths due to
an in-line, quasi 90 layout orientation.
The overall pressure drop of the 45*, 29.8% baffle cut tube bundle wasa) about 90% of the drop through a corresponding 900 bundle (Case 19) but
b) only about 40% of the drop through the previously tested Case 27 450
configuration with a 15.5% baffle cut.
Case 30
Case 30 is a 600 rotated triangular layout pattern, full tube bundle,
6-crosspass, 14-in. inlet/outlet, 15.5% baffle cut configuration. This
baffle cut is smaller than is conventional for industrial practice, sincethe small window areas promote relatively large window flow velocities and
large overall pressure drops. The small baffle cut was selected because 1)it is typical for the no-tubes-in-window bundle to be tested subsequently
and 2) it will provide a comparison with a following full bundle test with a
larger baffle cut. This test sequence had previously also been followed for
the 450 rotated square layout pattern. The 600 layout test exchanger wasflow tested with flowrates up to 0.161 m3/s (2550 gal/min). The results
indicate that the instability initiated at 0.150 m3/s (2370 gal/min) in thefar window and at 0.153 m3/s (2430 gal/min) in the near window, just
slightly above the threshold in the far window. This response is different
from all previously tested full tube bundles, in which the near window tubes
reached the instability threshold at a much higher flowrate than the far
window tubes. While this cannot be explained at this time, it may be noted
that compared to the other tube layout patterns, the 600 layout has a
smaller tube-to-tube gap in the drag (flow) than in the lift (transverse-to-
flow) direction, in which instability excitation usually initiates. As
usual, the instability initiated in the central region of the tube rows next
to the baffle cut, but it appeared that the second row from the baffle cut
vibrated more severely than the first. There are two contributing factors
that can explain this behavior. First, in the 600 layout, the second row of
tubes is almost as much exposed to the flow as the first row. Probably more
important is the second factor: even though the baffles theoretically do
not restrain the first row of tubes to move in the lift (transverse-to-flow)
direction, the nominal clearance between the baffle edges and tube row is
small (0.8 mm (0.031 in.)) and apparently inhibits the vibration response of
these tubes due to factors such as drag (flow) direction vibration, pressure
drop effects, and non-ideal structural support. Upon disassembly, contact
marks were found on the upstream corners of the baffle edges.
36
Case 31
For the Case 31 test the exchanger was taken apart and reassembled
without window tubes and with covered baffles to provide a 600 layout,
14-in. nozzle, 15.5% baffle cut, no-tubes-in-window (NTIW) configuration.
This baffle cut is typical for NTIW configurations, but generally considered
too small for full tube bundles as previously discussed. The NTIW bundle
was flowtested with flowrates up to 0.213 m3/s (3370 gal/min), when two of
the solid, stainless steel tie bolts that serve to hold the tube bundle
together, started to go into a strong instability. It should be pointed out
that these tie bolts are located in the far window and supported by only two
of the five baffles; such tie bolts would not be used in an actual no-tubes-
in-window bundle, where all tubes are supported by all baffles. Thus the
tie bolt instability has no practical importance but is of academic interest
because it may provide an instability data point. At flowrates up to 0.189m3/s (2990 gal/min) the vibration of the tubes was slight. At higher
flowrates the vibration of some tubes was considered moderate, but not
severe; this may or may not be acceptable for long term service. As during
previous NTIW tests, the relatively weak tie bars used to space the baffle
plates were vibrating vigorously. However, in an actual heat exchanger
these tie bars could readily be moved to a better location providing support
by all baffles.
Case 32
Case 32 is a 6-crosspass, full bundle, 600 layout, 14-in. nozzle
configuration with an increased 29.6% baffle cut obtained by trimming the
baffles accordingly. The range of flowrates at which fluidelastic
instability initiated during different test runs was somewhat larger than
experienced for most other configurations; the lowest threshold flowrate
observed was 0.116 m3/s (1840 gal/min). Again the instability initiated in
the central region of the two tube rows next to the baffle edge in the far
window (opposite the nozzles). As the flowrate was increased, the region of
instability extended to the tubes near the shell periphery first on the
bottom, later on top; at a still higher flowrate 0.206 m3/s (3270 gal/min)
instability initiated in the central region of the tube rows next to the
baffle edge in the near window.
In contrast to the corresponding 45* test, Case 29, there was
considerable "hysteresis" of the central far window tubes which at times did
not drop out of instability until the flow was reduced to 0.084 m3/s
1330 gal/min).
Case 33
Case 33 was obtained by rotating the Case 32 bundle by 90 to provide a
6-crosspass, full bundle, 600 layout with the baffle edges oriented parallel
to the inlet/outlet nozzles. This forces the flow to make a complex 90*
turn before and after negotiating the first and last baffles,
37
respectively. The first flow-turnaround window was located on the bottom ofthe tube bundle. The fluidelastic instability initiated in a group of
three-span tubes in the "corner" region between the baffle edge and theshell periphery exposed to the inlet flow. The lowest threshold flowrate
was 0.100 m3/s (1590 gal/min). As the flowrate was increased, the region of
tube instability expanded away from the nozzles in the tube rows near the
baffle edge. The occurrence of tube instability of the four-span tubes (in
the opposite window) could not be positively identified as flowrates up to
0.189 m3/s (2990 gal/min) were applied.
A more detailed discussion of the implications of parallel-to-nozzleaxes baffle cuts is presented in the following section in conjunction with
test cases 36 and 38.
Case 34
Case 34 is a 6-crosspass, 14 in. nozzle, 600 layout configurationwithout window tubes and with covered baffles to provide a 29.6% baffle cut,
no-tubes-in-window configuration. Also, the bundle was repositioned to
orient the baffle edges transverse to the inlet/outlet nozzles, as provided
for all previous tests except Case 33. Thus this test serves to provide a
comparison with a previous 600 NTIW test with a smaller baffle cut,
Case 31. At increasing flowrates up to 0.182 m3/s (2880 gal/min) thevibration of the tubes was slight. At that flowrate a group of tubes in the
central core of the tube bundle began a strong buzzing type vibration,probably due to an instability and considered to be unacceptable. As the
flowrate was increased to 0.203 m3/s (3220 gal/min) the region ofinstability increased, however the vibration of the tubes on the sides of
the tube bundle (i.e., in the outside rows) remained generally moderate. Asduring previous NTIW tests, the relatively weak tie bars used to space the
baffle plates were vibrating vigorously.
Discussion
During the 450 and 600 layout pattern tests the fluidelastic
instability initiated also in the central region of the rows adjacent to the
baffle cut. However, there were differences in response, apparently due to
fundamental flow/geometry differences. Unlike the 300 or 900 layouts, the
600 and 450 layouts obtained by rotation of the respective identical
patterns, present the narrowest tube-to-tube gaps in directions at angles to
the overall flow (drag) direction. There are two significant consequences
on the velocity distribution.
First the highest velocities and accelerations of the flow passing
through the bundles are not perpendicular to the transverse-to-flow (lift)
direction in which instability excitation usually initiated for 90 and 300
and in which more distance (i.e., amplitude) is or would be required fortube-to-tube impacting. One of the apparent consequences was that the
threshold of instability could not always be so well defined and was not so
38
consistent (with flowrate) as had been the case for the 300 layout tests.
During the test of the 450 bundle with conventional 30% baffle cuts (Fig.
4a) the initiation of instability was sensed as a severe vibration, but not
accompanied by as dramatic a rise in amplitudes as had been observed during
other tests. Visual observations indicated that a fair part of the flowbypasses the central core of the 450 bundle not only by leakage between the
bundle and the shell but also by short-cuts through the first and second
tube gaps from the bundle exterior where these present reduced resistance
flow paths due to an in-line, quasi 90* layout orientation.
Second, for an equal approach flow velocity entering comparable 900 and300 layouts with a P/D = 1.25, the maximum mean gap flow velocities are
reduced to 71% and 87% in corresponding 45* and 600 layout bundles,
respectively.
The above differences in flow distribution are reflected in thedifferences (and difficulty of evaluation) of the vibration response for the
450 and 600 as compared to the 900 and 300 tube bundles. It is interesting
to note that with respect to acoustic excitation from gas flow, the 45*
layout is particularly susceptible. Understanding cf the 450 bundle
behavior could provide one of the basic keys for solving flow-inducedvibration problems in tube bundles.
The no-tubes-in-window tube bundles did not experience tube-to-tubecollisions. However, vigorous tube vibration was observed at various
locations at the flowrates indicated on Table 6. It is interesting to note
that considerably less than the theoretical approximately four times
increase produced instability in NTIW bundles with half the longest span
length as comparable to the full bundle. No doubt the velocity distribution
across critical tubes contributed. To the best of the authors' knowledge,
industry to-date has not reported any vibration problems of NTIW tube
bundles during field operations. It may be noted that an industrial
designer would provide all tubes in the external tube rows with full 3600
circumirerential support in complete baffle holes. This practice eliminates
the limited partial support available to saddled tubes, which were at times
the most susceptible ones in the test exchanger to vibrate.
B. 300 and 900 Layout, 7-Crosspass Configurations (Cases 35-38)
All previous tests were performed with bundles having an even number of
equal crosspasses, namely six and eight. For transverse cut baffles with
edges oriented perpendicular to the nozzle axes, the shell nozzles are on
the same side of the shell (Fig. 3). This results in the baffle-windowtubes nearest the nozzles being supported by one more baffle than those
baffle-window tubes on the opposite or "far" side of the bundle. Vibration
always first started in the "critical row" tubes just beyond the baffle edge
in the "far" baffle window. Since for bundles with an even number of
crosspasses the tube support is different for tubes in the "far" and "near"
window regions, it was suspected that a different situation would result for
39
bundles with an odd number of crosspasses in which the tube support is thesame in both baffle windows (Fig. 5). However, because of the respective
expansion and contraction flow conditions in the nozzle end zones, the flow-
induced excitation conditions are not the same in the two w'_ndow regions.
Thus, to examine the vibration susceptibility of "far" versus "near" window
tubes and also to provide a comparison with the 6- and 8-crosspass tests,
the bundle was configured with seven equal crosspasses and representative
tests were repeated.
Unlike the even-numbered crosspass configurations, the odd number of
crosspasses requires the inlet and outlet nozzles to be~on opposite sides of
the shell as shown on Figs. 2 and 5. To provide this, the modular shell
section with the outlet nozzle was rotated by 1800. Additional pipe taps
were installed for pressure drop measurements. The exit piping to the
supply tank required rerouting of some existing components as well as
construction of a new 8-inch plastic pipeline connection.
All four 7-crosspass (6-baffle) configurations tested involved full
tube bundles with a 29 or 30% baffle cut and 10 in. size nozzles. The four
tests investigated both 300 triangular and 900 square layouts both with
transverse and parallel baffle cuts. Typical tube layouts are shown on
Fig. 6. The detailed results are presented on Table 7 and comparative data
are listed on Table 8.
Case 35
Case 35 is a 7-crosspass, 300 layout, 10-inch nozzle, full tube bundle
configuration having a 28.9% transverse baffle cut, i.e., with baffle edges
oriented normal to the inlet and outlet nozzles. The tubes in the "near"
and "far" windows have identical support but different shellside flow
conditions as discussed above. Flowtesting indicated that instabilitiesinitiated in both windows at about the same flowrate, but not
simultaneously. The lowest instability threshold was observed at 0.172 m3/s(2720 gal/min) in the "near" window but during an additional test run
instability initiated first in the "far" window at a slightly higher
flowrate. The tubes involved, as in most previous tests, were located in
the central region of the rows adjacent to the baffle edge. The instabilitythreshold results as well as the pressure drop measurements fell in-between
the corresponding data obtained from previously tested 6- and 8-crosspassbundles.
Case 36
Obtained by rotating the Case 35 bundle by 90*, Case 36 is a
7-crosspass, 30* layout, 10-inch nozzle, full tube bundle configuration with
a "vertical" baffle cut that orients the baffle edges parallel to the inlet
and outlet nozzles. This forces the flow to make a complex 90* turn before
and after negotiating the first and last baffle, respectively. The first
flow-turnaround window is located on the top of the bundle. The
40
3.58 m(14(
BAFFLESPACING(T YP)
A
x.75 in.) TUBE LENGTH INSIDE SHELL7 SPAN TUBE
OBSERVATION 4 SPAN TUBEPORT (TYU)
OUTLET
~~1B qL11 1 AL
. . ..................
NI
INLET
-0.59m (23.25in.) SHELLINSIDE DIAMETER
TOP VIEW
TUBES3 BAFFLE SUPPORTS BAFFLE CUT (WINDOW)4 SPANS (3 ea.O.286 0.296 DIAMETER (TYF)AND lea. 0.143 TUBELENGTH) -
TUBE S6 BAFFLE SUPPORTS7 EQUAL SPANS
VIEW AA VIEW BB
Fig. 5. Test exchanger in 7-crosspass/6-baffle configuration (Case 37 shown)
J -0
U6
- C
FLOWQ(
INLET >0(_NOZZLE 'S" Y' 'C >.0 o '/
Q (_
u u
Case 35F-P-7-10"-30*-29%TC
- )000 - 0000 OC0 ",,(
/ O0 000 '( 0C'0 N
8800 (' )00(, ; ',c0300FLOW I OU ) C OC), )(A)O
INLETe O c c n
\ 0000 )oO:' X0000
000000 naCo00000.ooo UyC00 -900000/
INLET\ O OOcO~ 'U "o0 0000NOZE 0000000N-1 '- ) 0O0-- oo00oyQQ0QQ 'O 0000
0000 00c . ;)000000
000000 000<00Ong c O "
Case 37F*P 7 "l0" "9Q0 30%TC
Fig. 6. Schematics of typical 30* and 900 test configurations
- rI
III
I W
r
L L
41
Table 7. Flowrates associated with instability and tube impacting r withlarge vibration amplitudes at different locations in tube bundle.Cases 35 to 38
7-crosspasses, full tube bundles, 10-in. imuies.-5 3Flowrates in gal/mmn (1 gal/mmn = 6.309 x 10 m /s)
35300
CaseLayout
Baffle Cut
Orientation28.9
Transverse
36300
37900
28.9 29.6Parallel Transverse
Location and Instability phenomenon
Far (1st, 3rd, 5th) window, centralregion, near baffle edgeImpacting initiatesImpacting ceases
Far window, baffle edge/shell corner
Frequency response/large amplitudeImpacting probableImpacting ceases
Near (2nd, 4th, 6th) window,central region, near baffle edgeImpacting initiatesImpacting ceases
27702540
2270*2120
20801990*1960
2720* 26702370
* Identified as the lowest critical flowrate
** Case 36 and 38: Corner region nearest nozzles in first window
3j
900
29.6Parallel
23702190
1950*
42
Table 8. Critical flow parameters of 300 and 90* layout, 7-crosspass test exchanger configurations
*Lowest TypicalCritical or ExperimentaltInstability Computed and InstabilityThreshold Cap Flow Theoretical Reduced**, Threshold
Case ** Flowrate Velocity,U Frequency,f Velocity ConstantNo. Configuration Code Location m3/s gal/min m/s ft/s Hz U B
35 F.P'7.10""30* 29%TC FBE 0.175 2770 2.08 6.82 20.5 Ex 5.32 6.5629.9 Th 3.65 4.50
NBE 0.172 2720O 2.05 6.71 21.0 Ex 5.11 6.3029.9 Th 3.59 4.42
36 F.P.7.10".30*%29%PC FCR 0.126 1990 1.42 4.66 25.0 Ex 2.98 3.6729.9 Th 2.49 3.07
37 F.P.7.10".90*%30%TC FBE 0.143 2270*t 1.76 5.79 25 Ex 3.71 4.6830.7 Th 3.02 3.82
38 F.P.7.10".90*.30%PC FCR 0.123 1950* 1.27 4.18 32 Ex 2.09 2.6430.7 Th 2.18 2.75
FBE 0.150 2370 1.44 4.71 27 Ex 2.79 3.5330.7 Th 2.45 3.10
48 U.P4.10".30*%29%TC FBE 0.182 2880*t 2.17 7.11 20.0 Ex 5.69 7.0119.6 Th 5.80 7.15
FBE 0.198 3140 2.36 7.75 23.5 Ex 5.28 6.5019.6 Th 6.33 7.79
FBE 0.198 3140 2.36 7.75 32.5 Ex 3.82 4.7034.4 Th 3.60 4.44
* Lowest critical flowratet Flowrate of threshold initiating "classic" fluidelastic instability
** Location code: F - far or first window, N - near windowFollowing letters: BE - next to baffle edge, CR - corner region nearest nozzle
tt Instability initiation based on frequency response criteria*** 0 - U/fD; D - 19.1 mm (0.75 in.)ttt Case 48: Data before and after shift from 1st to 2nd mode
43
fluidelastic instability initiated in a group of tubes in the "corner"
region between the shell periphery and the edge of the first baffle exposed
to the inlet flow. Analysis of the data indicated that one of the
instrumented tubes (the fourth from the front) adjacent to the baffle edge
was subjected to a local instability with vibration amplitudes increasing
gradually with flowrate; a threshold was reached when this tube began
impacting at 0.126 m3/s (1990 gal/min). While all tubes in this affectedcorner region were visually observed to vibrate actively, impacting of other
instrumented tubes there could not be ascertained until somewhat higher
flowrates were applied. Here also amplitudes rose more or less gradually
with flowrate. There was little hysteresis upon flow reduction. The tubes
in the last turnaround window connected to the outlet nozzle were not
noticed to go unstable at flowrates up to the 0.172 m3/s (2720 gal/min)
applied. The overall pressure drop was about 5% less than when the bundle
was oriented with a transverse baffle cut requiring a slightly longer flow
path during the previous Case 35 test.
Case 37
Case 37 is a 7-crosspass, 900 layout, 10-inch nozzle, full tube bundle
configuration having a 29.6% transverse baffle cut. The fluidelastic
instability initiated in the central region of tube rows next to the baffle
edges: in the "far" and "near" windows (with respect to the inlet nozzle)
the thresholds were significantly different: 0.143 m3/s (2270 gal/min) and
0.168 m3/s (2670 gal/min), respectively. Some tubes located on the
periphery of the tube bundle were excited to substantial vibration
amplitudes that gradually increased with flow. The pressure drop was
reduced by about 23% compared to a previously tested corresponding
configuration with a 300 layout (Case 35).
Case 38
Obtained by rotating the Case 37 bundle by 900, Case 38 is a
7-crosspass, 90* layout, 10-inch nozzle, full tube bundle configuration with
a parallel baffle cut. Significant vibration activity began in a group of
tubes in the "corner" region between the shell periphery and the edge of the
first baffle exposed to the inlet flow. With vibration amplitudes
increasing gradually with flowrate, these tubes began to vibrate vigorously
at about 0.123 m3/s (1950 gal/min), apparently impacting in the baffle holes
due to a local instability. The occurrence of tube-to-tube collisions could
not be positively identified until higher flowrates were reached. At
0.150 m3/s (2370 gal/min) an abrupt-with-flowrate instability initiated in
the central region of the rows next to the baffle edge in the firstwindow. Upon flow reduction this instability ceased at 0.138 m3/s
(2190 gal/min). The tubes in the last flow-turnaround window connected to
the outlet nozzle were not observed to go unstable up to the maximum
flowrate of 0.175 m3/s (2770 gal/min) applied. The overall pressure drop
was about 8% lower than for the Case 37 bundle with the transverse baffle
cut orientation.
44
Discussion
The test results obtained from the 7-crosspass test series indicate
that the instability thresholds with respect to flowrate and mean gap
velocity were found to be within the values obtained from the corresponding6- and 8-crosspass tests as indicated on Table 13 in Section V. It appears
that the 7-crosspass bundle performs as well if not a little better than
would be expected from a simple interpolation of the 6- and 6-crosspass test
results. The similar support conditions in both the "near" and "far"windows were probably of some advantage. With respect to the instability
thresholds of the "near" and "far" windows with transverse baffle cuts there
was some difference with respect to layout. For the 300 layout the
threshold was about the same for both windows. This corroborates reasonablywith Kissel [19], who, reporting on 300 layout tests found instability to
first develop in the near window. However, for the subject 90* layout tests
(Case 37) the threshold for the near window was about 18% higher than for
the "far" window. Still, this percentage is much less than the more than
40% experienced for corresponding 6- and 8-crosspass tests.
Along with test Case 33, the 7-crosspass test Cases 36 and 38
investigated for the first time during this program the effect of parallel-
to-nozzle axes baffle cuts. Even though the tested tube bundles were
identical to those tested with the corresponding transverse baffle cut
orientation (i.e., Cases 32 and 35 and 37, respectively), the 90* difference
in orientation makes a significant difference. This is particularly true
for the triangular layouts, where a 30* layout presents a 600 layout
orientation to the flow entering and leaving through the end zones. With
the baffle edges oriented parallel to the nozzles, the flow is forced to
make a complex 900 turn before and after negotiating the first and last
baffles respectively. In the first flow-turnaround window in the "corner"
formed by the baffle edge and the shell periphery, there are tubes that are
not supported by the first baffle and that are also very close to the flow
discharging from the inlet nozzle. This permits part of the flow to take a
short cut into the second crosspass. It was thus not unexpected that the
test results indicated that there is a potential for vibration to develop in
these "corner" regions. As seen from Tables 6 (Case 33) and 8 (Cases 36 and
38) the thresholds for instability and/or unacceptable performance lie
substantially below those obtained from the corresponding configuration with
"horizontal" baffle cuts.
There is, however, another factor to be mentioned. Even though
occurring at lower flowrate, the unacceptable vibration performance in the
"corner" region of a parallel baffle cut exchanger may involve relatively
few tubes compared to a larger number of tubes that develop instability in
the central region of the first window at a higher flowrate. The practical
significance for an exchanger experiencing a vibration problem in the field
is that the diagnosis of "corner" region vibration may permit a much simplerremedy (such as plugging a few tubes) than would be necessary to correct a
major instability.
45
C. 300 Layout Double-Segmental Baffle Configurations (Cases 39-42)
One of the techniques used by designers of shell-and-tube heat
exchangers when they encounter a potential flow-induced vibration problem isto shift from a tube bundle with segmental baffles to one with double-
segmental baffles. This results in a split of the flow in either side of
the shell with lower velocities and the possibility to reduce the
unsupported span length while keeping below a given allowable pressuredrop. Thus the testing of double-segmentally baffled configurations to
compare their vibration performance with single-segmental baffled
configurations was of interest.
The new 300 and 450 layout double-segmental baffles were fabricatedwith the same overall dimensions and clearances as the previously testedsingle segmental baffles, and used with the same basic shell, tubes, and
tubesheets. The 30* configurations were tested first (Fig. 7).
All of the 300 triangular layout double-segmental baffle full tube
bundle configurations tested had the following features: six equal
crosspasses, 10-in. size nozzles, and 19.1 mm (0.75-in.) 0.D. plain tubesspaced with a pitch-to-diameter ratio of 1.25. The difference in the four
test cases was the order of placement of the two different kinds of double-segmental baffles, "core" and "wing," and the orientation of the baffle
cuts. See Figs. 8 to 10. The first pair of tests used three "core" and two"wing" baffles, thus placing the "core" baffles nearest the nozzles. The
second pair of tests used three "wing" baffles and two "core" baffles. Theinstallation of a "core" baffle results in a pair of outer baffle windows;
correspondingly, a pair of "wing" baffles creates a central baffle window in
the space between them.
Each of the two pairs of tests was performed with baffle edges oriented
parallel and transverse to the centerline axes of the nozzles. The detail
results are presented on Table 9. To facilitate comparison of all double-
segmentally baffled tests, the critical flow parameters are included in
Table 11 and the locations of major vibration response are illustrated on
Fig. 13, both presented in Section IV.D. It should be noted that those
combinations of baffle arrangement and cut orientation which produce longunsupported tube spans immediately below the nozzle would normally not beselected by knowledgeable designers. However, they were included to
complete the test matrix and to demonstrate their potential for damaging
vibration.
Case 39
The most usual arrangement of baffles and cut is that used for this
case. This 3 core/2 wing baffle arrangement with parallel cut locates theleast supported 3-span tubes in the outer windows. These windows have
"corner" regions located between the shell periphery and the top and bottom
46
Fig. 7. Double-segmental baffled tube bundleANL Neg. No. 113-84-53.
A0Qa~113
El
during assembly (Case 39 shown).
)
42,47 41,46Parallel Trans-
verse
Case numbers
Baffle edgeto nozzle axes
orientation
Baffles
Fig. 8. Double-segmental baffle arrangement and orientation combinations
39,43,44Parallel
40,45Trans-
verse
47
1, - 3 58 m (140.75 in. ) TUBE LENGTH INSIDE SHELL
'CORE" BAFFLE
BS
BA
AFFLEPACING(TYP)
ING AFFLE
OBSERVATION PORT
A B
3 SPAN TUBE
6 SPAN TUBE
4 SPAN TUBE
n-
T - -I if I/~TN I11
I_ IiII--- -F ' 1i
IL
I11---- -- -I[-I P=1I 11
A ' B
[_ TUBES -LO59m (23.25 in.) SHELLTUE-INSIDE DIMETER H5 BAFFLE SUPPORTS
6 EQUAL SPANS
CENTRAL "WINDOW "0.344 DIA. (TYP.)
TUBES - VIEW A-A2 BAFFLE SUPPORTS ,,OE A3 EQUAL SPANS BAFFLE "OVERLAP
3 EQAL SANS0.075 DIA. (TYP.)
TUBES -
3 BAFFLE SUPPORTS4 SPANS (2 EA. 0.167
o AND 2 EA. 0.333TUBE LENGTH
0
VIEW B- B BAFFLE CUT (" WINDOW")0.253 DIA. (TYP )
Fig. 9. Test exchanger in 6-crosspass, double-segmental baffleconfiguration (Case 40 shown)
00000( Th0( : vC A20
,'00'~0 00000000L00 O0.)000uw0K (-oOOr)*ooooOc ~ H >ocorob 'oooe\
FLOW 00 r- hJC)Q00U GOC_ J000 000 000 00:)' 0O0C C 000O000coo1Do '0000000o"-1 00oooo
INLET 0000 c,70 C-,0 c '000000.,'7c00000000000000 00C00000NOZZL00000 C '000000
00000cGC00 "T,00000000000000&00000 00000\
O00)0000000
Cases 39 and 42
INLETNOZZLE 3 8 ('
C0ses0a. 4OO nQCO, 0 Vi , n)
Cases 40 and 41
Fig. 10. Schematics of 30* double-segmental baffle test configurations
nF
- t Ii ~
INLETTOP VIEW
OUTLET
-- j 16I -i--- II .I - 1 V
--
rL -9
Ii
-1
48
Table 9. Flowrates associated with instability and tube impacting or withlarge vibration amplitudes at different locations in tube bundle.Cases 39 to 42
300 triangular layout, double-segmental baffles, 6-crosspasses, 10-in. nozzles
Flowrates in gal/min (1 gal/min = 6.309 x 10-5 m3/s)
CaseNumber of "Core" BafflesNumber of "Wing" BafflesBaffle Cut Orientation
3932
Parallel
40 41 423 2 22 3 3
Transverse Transverse Parallel
Location and Instability phenomenon
Window
At central baffle edgeAmplitude increaseInstability initiatesImpacting initiatesImpacting ceases
Window
Tubes at baffle edge/shellintersection nearest nozzleFrequency responseImpacting initiates
WindowTubes under nozzleAcceleration amplitudeActivity increases abruptlyInstability ceases
Outer, Outer,top bottom
2840*2500
Outertop
corner
32803190
Outer, Central, Central,near near far
24502360
Outerbottomcorner
2590*2570
279029603090
Centraltop andbottom
2640 2320
Outer
1830*1650
2550
Outer Central
2540 2500*
2430
* Identified as the lowest critical flowratet Baffle cuts: Core 25.3%, Wing 32.8% (from shell ID), overlap 7.5%
49
edges of the core baffles. In the "corners" located nearest to the nozzles,
the shellside water flow short-cuts much of the end zone regions. Prior to
reaching major instability thresholds, groups of tubes in these "corner"
regions exposed to the inlet flow responded with significant vibration
levels even though no tube-to-tube collisions could be verified at that
time. For instance, an instrumented tube located in the bottom "corner"
region indicated amplitudes gradually rising with flowrate to 8% of the tube
diameter (peak-to-peak) at 0.146 m3/s (2320 gal/min), when a very sharp
peaked spectrum at 22.5 Hz indicated an instability based on the frequency
response criterion. These amplitudes are sufficiently high to cause concern
for acceptable long term performance.
Major abrupt-with-flowrate instabilities initiated in the central
region of the tube rows next to the edges of the core baffle at 0.179 m3/s
(2840 gal/min) and at 0.207 m3/s (3280 gal/min) in the top and bottom outerwindows, respectively. There is no obvious explanation why the tubes went
unstable in the top well before the bottom outer window, since theoreticallythe flow is expected to be divided equally. One may speculate that this is
due to a leakage path between the top of the baffles and the shell where themajor portion of the shell-to-baffle clearance appears because gravity rests
the tube bundle on the bottom of the shell.
The tubes in the central baffle window have four spans, two short and
two twice as long. At the higher flowrates about half of these tubes
closest to the nozzle responded with severe high frequency (about 95 Hz)
buzzing vibration. However, no appreciable vibration amplitudes were
measured by two instrumented tubes in this region. The reason, in part, is
that the accelerometers were located (along the tube axis) to optimally
sense first and second mode vibrations. This location was not as suitablefor sensing the higher mode vibration actually encountered. The
accelerometers were repositioned during some of the following tests.
It also appeared that the tubes directly exposed to the inlet flow were
not as active as the tubes located i the second row behind them, a
phenomenon that had been observed previously in the test configurations
having 600 layout patterns; this pattern of course is encountered by the
flow of the subject 300 bundle in the inlet and outlet zones.
Case 40
For this test, the tube bundle was rotated by 900 to provide atransverse baffle cut configuration (Fig. 9). Since one of each pair of the
outer baffle windows was next to the inlet/outlet nozzles, these nearbyouter windows could be expected to draw more than half of the flow. Indeed,
during flow testing only tubes in these nearby windows were excited intoinstabilities. First, the tubes in the rows directly exposed to the nozzle
flow went unstable at 0.115 m3/s (1830 gal/min). An instrumented tube
indicated that the vibration occurred at a frequency associated with the
second mode, which, in contrast to the first mode, has much larger relative
50
amplitudes in the end spans than in the center span of the 3-span tubes.
Apparently the effect of the inlet (and outlet) flow on these end spans is
sufficiently strong to dominate the usually more easily excited fundamental
first mode vibration. Going to higher flowrates an instability initiated in
the tubes in the rows next to the edge of the core baffle at 0.155 m3/s
(2450 gal/min). At that location, significantly, an instrumented tube
indicated that its vibration frequency shifted down from the second to the
first mode (27 to 17.5 Hz) as the tube became unstable. There was no
evidence of significant vibration for the 4-span tubes in the central baffle
window up to the 0.174 m3/s (2760 gal/min) flowrate tested.
Case 41
For the Case 41 and 42 tests, the tube bundle was reconfigured with
three "wing" and two "core" baffles (Fig. 8). This arrangement locates the
3-span tubes in the central baffle window region of the bundle and the 4-
span tubes in the outer baffle windows, with the short spans in the nozzle
end zones.
Flow testing resulted in fluidelastic instabilities in the centralwindow in the rows of tubes next to the edges of the "wing" baffles. The
first instability initiated at 0.163 m3/s (2590 gal/min) on the side closestto the nozzles at the fundamental natural frequency of about 20 Hz. There
was little hysteresis. A second instability started on the opposite side at
a higher, not well defined flowrate of about 0.187 m3/s (2960 gal/min).
Finally, most of the tubes in the central baffle window were vibrating. Itshould be pointed out that selected tubes immediately under the nozzles
vibrated at a higher mode frequency (about 98 Hz) at flows somewhat lower
than required for instability. The amplitudes were small and not sufficient
to cause tubes to collide, but the accelerations (e.g., 11 g singleamplitude at 0.160 m3/s (2540 gal/min)) were high enough to cause concern
for long term ; ar at the baffles.
Case 42
For this test the tube bundle was rotated by 900 to provide a"vertical" baffle cut configuration, with baffle edges oriented parallel to
the nozzle axes. This arrangement locates the least supported 3-span tubesin the central baffle window directly in the path of the nozzles. Upon
testing the instability initiated in the central window tubes closest to thenozzles at 0.158 m3/s (2500 gal/min); the region of instability extended
about 4 to 6 rows into the bundle. The acceleration signals from a tube
directly exposed to the nozzle indicated that it vibrated with a frequency
(about 26 Hz) considered to be associated with the second mode and uponinstability initiation shifted up (to about 35 Hz) into what is believed to
be third mode vibration. Up to the 0.164 m3/s (2600 gal/min) flowrate
tested, no significant vibrations were observed in other regions of the
bundle.
51
Discussion
Double-segmental baffled heat exchangers are subjected to inherent flow
maldistributions. The effects on vibration response are included in the
"discussion" chapter at the end of Section IV.D.
D. 450 Layout Double-Segmental Baffle Configurations (Cases 43-47)
The testing of the 450 rotated square layout double-segmental baffle
full tube bundle configurations followed essentially the same sequence as
the 300 layout tests. The difference in the four basic test cases was theorder of placement of the two different kinds of double-segmental baffles,
"core" and "wing," and the orientation of the baffle cuts. See Figs. 8, 11,and 12. The first pair of tests used three "core" and two "wing" baffles,
thus placing the "core" baffles nearest the nozzles. The second pair of
tests used three "wing" baffles and two "core" baffles. Again each of the
two pairs of tests was performed with parallel and transverse-to-nozzle axes
baffle cut orientations. The results are presented on Table 10 and
illustrated on Fig. 13. The critical flow parameters are included in
Table 11.
The four basic test cases (43, 45, 46, and 47) were tested with 10-in.s.ze nozzles; Case 44 is a re-test of the Case 43 bundle with 14-in. size
nozzles to determine the effect of lower nozzle velocities.
Case 43
This test case had a 450 layout, 10-inch nozzle, 3 core/2 wing baffle
configuration with parallel baffle cuts. The responses of the 4-span tubes
in the central window and the 3-span tubes in the outer windows were
fundamentally different. The 4-span tubes under the nozzle vibrated at a
frequency of approximately 100 Hz, probably representative of 5th (or 6th)
mode vibration which has the largest relative amplitudes in the short span
exposed to the nozzle flow. This is where the instrumentation was
located. The generally gradually increasing amplitude versus flowraterelationship of a front tube indicated a moderate "jump" starting at about
0.145 m3/s (2300 gal/min) with a rise from about 1 to 5% of diameter peak-
to-peak amplitude. Thus the above flowrate is quoted as the lowest critical
flowrate. With increased flow the buzzing became a very severe vibration
when at 0.215 m3/s (3400 gal/min) a peak-to-peak amplitude of 0.25 diameters
was attained at 121 Hz; this represents single amplitude acceleration level
of 138 g.
The 3-span tubes in the outer windows responded with the fundamentalnatural frequency of about 20 Hz. The largest peak-to-peak amplitude
measured at the 0.145 m3/s (2300 gal/min) flowrate mentioned above was about
4% of diameter and involved a tube that was located one row distant from the
edge of the baffle in the central region of the bottom outer window. With
increased flowrates most of the tubes in the bottom window began to vibrate
52
3.58 m (140.75 in. ) TUBE LENGTH INSIDE SHELL
CORE" BAFFLE
BAFFLESPACING
(TYP)
"WING
BAFFLE46 sussu E
OBSERVATION PORT
A B
tI
- -I -
-1 IINLET
3 SPAN TUBE
6 SPAN TUBE
4 SPAN TUBE
r.
1[l' 1 ~ .
II =
II
A BTOP VIEW
IL '1
M +OUTLET
L0.59m (23.25 in.) SHELL 5 BAFFLE SUPPORTSINSIDE DIAMETER 6 EQUAL SPANS
CENTRAL "WINDOW "0.336 DIA. (TYP.)
TUBES - / VIEW A-A2 BAFFLE SUPPORTS BAFFLE"OVERLAP13 EQUAL SPANS 0.062 DIA. (TYP.)
TUBES -3 BAFFLE SUPPORTS4 SPANS (2 EA. 0.167
0 AND 2 EA. 0.333TUBE LENGTH
VIEW R-B BAFFLE CUT ("WINDOW')0.264 DIA. (TYP.)
Fig. 11. Test exchanger in 6-crosspass, double-segmental baffleconfiguration (Case 45 shown)
e'0
INLET 0NOZZLE -) C
Cases 43 and 47
000 O0 q 0
FLOW K CoOO CO~~OO,',j0 c0 0 c ac OcuO
.>>000 )0 000
)U CU 000 00001=00 OO CC 0000 000 /1
NOZZLE G)) j CU
001 00 OO C "UC x1 (UC.)-0000000 01i
" bO
Cases 45 and 46
Fig. 12. Schematics of 45* double-segmental baffle test configurations
H-4 ii RE I!-i
rt
I
1 11
Itj r=Kr-7r=
53
Table 10. Flowrates associated with instability and tube impacting or withlarge vibration amplitudes at different locations in tube bundle.Cases 43 to 47
450 rotated square layout, double-segmental baffles, 6-crosspasses
Flowrates in gal/min (1 gal/min = 6.309 x 10 5 m3/s)
CaseNumber of "Core" BafflesNumber of "Wing" BafflesBaffle Cutt Orientation
Nozzle size, in.
4332
Parallel
10
4432
Parallel
14
4532
Trans-verse
10
4623
Trans-verse
10
Location/instability phenomenon
Window
Near central baffle edgeAmplitud'i increaseAmplitude peakImpacting probable
Window
Tubes at baffle edge/shellintersection nearest nozzlesAmplitude increaseAmplitude peakImpacting probable
WindowTubes under nozzleAmplitude increaseAmplitude decreaseLarge accelerationImpacting burstsImpacting steady
Outerbottom
2350
3400
Outer
bottomcorner
Outerbottom
3050
Outer
bottomcorner
Outer
topcorner
2500*
3400 3050 3500
Central Central
2300*2200
3590
Outer Centralnear near
2510*3060
Outernear
3550
Centraltop
25102350*
Outer Outer Central
1860*29503100 2540
4723
Parallel
10
* Identified as the lowest critical flowratet Baffle cuts: Core 26.9%, Wing 33.2% (from shell ID), overlap 6.3%
54
Case Configura- Observationstion Code Flowrates in gal/sin
39 D-C-6-10" " Gradual amplitude increase in30*-25%PC outer/window shell "corner" re-
2640 gions at 23202140 e Instability, in central outer
window, row adjacent to core3280 baffle: top 2840*t, bottom 3280
2320
40 D-C-6.10" " Instability at 1830*, near outer30*-25%TC window tubes under nozzle, sec-
1830 ond mode" Instability at 2450t, row adja-
cent to core baffle, shift fromsecond to first mode
t.450
41 D-W-6-10"30*-25%TC
2594
2960
* Instability, central window, rowadjacent to wing baffle edge
Nozzle side at 2590*tAway from nozzle side at 2960
" High frequency ('100 Hz) "buzz,"tubes under inlet nozzle
42 D.W-6.10" e Instability in central window at30"25%PC 2500* and 2550t, under nozzle,
2500 extended 4 to 6 rows intobundle, 2nd to 3rd mode fre-quency shift of tubes in let row
25 0
43 D-C-6.10' " Instability ill defined, occurs454*27%PC at 2300* in tubes under inlet
2100 nozzle at ~100 lz (5th or 6th
mode)* Instability, bottom outer window
3460 tubes at 3400t
44 D-C-6-14" * Step-wise increase of amplitude45*"27%PC of bottom outer window tubes at
3500 2500*" Instability ill defined at 3050t3050* High frequency response underinlet nozzle
2509
45 D-C-6-10" -"
45*27%TC2950
I
2510, 3060
Instability ill defined at 2510*as near outer window tubes peakin row adjacent to core baffleInstabilty of tubes under inletnozzle at 2950Instability ill defined at 3060t
46 D-W-6-10" High acceleration levels at45*-27%TC 1860* in front row at 77 Hz
1860,2400 " Strong "buzzing" in near outerwindow under nozzle at 2400
1"Instability on near side ofcentral window at 3550t
47 DW-6.10" * Instability at 2350*t in front45 *-27%PC tubes near baffle edge row of235025 central window
20 Instability extends 9 rows deepinto central window at 2810
2540
For * and t see Table 11.
Fig. 13. Principal observations of double-segmental baffled configuration tests
55
Table 11. Critical flow parameters of double-segmental baffled test exchanger configurations
*Lowest Typical
1Critical or ExperimentalBaffle Instability Computed and Reduced InstabilityArrange- Threshold Gap Flow Theoretical Velocity Threshold
Case ment Flowrate Velocity,U Frequency,f *** ConstantNo. Configuration Code ** m3/s gal/min m/s ft/s Hz U S
39 D.C.6.10"'30*%25%PC 3C/2W 0.179 2840 1.05 3.46 20.0 Ex 2.77 3.4122.9 Th 2.42 2.98
40 D.C.6.10".30*.25%TC 3C/2W 0.115 1830 0.79 2.58 28.0 Ex 1.47 1.8222.9 Th 1.80 2.22
0.155 2450 1.05 3.45 27.0 Ex 2.04 2.5222.9 Th 2.41 2.97
41 DeW6.10".30*.25%TC 3W/2C 0.163 2590 1.10 3.62 20.0 Ex 2.90 3.5722.9 Th 2.53 3.12
42 D.W.6.10".30*.25%PC 3W/2C 0.158 2500* 0.93 3.06 26.0 Ex 1.88 2.3222.9 Th 2.14 2.63
0.161 2550 0.95 3.12 35.0 Ex 1.43 1.7622.9 Th 2.18 2.69
43 D.C.6.10""45*.27%PC 3C/2W 0.145 2300 0.66 2.17 101. Ex 0.34 0.4324.4 Th 1.42 1.80
0.215 3400 0.96 3.16 22.5 Ex 2.25 2.8423.5 Th 2.15 2.72
44 D.C6.14""45*%27%PC 3C/2W 0.158 2500 0.72 2.36 19 Ex 1.99 2.5123.5 Th 1.61 2.03
0.192 30501 0.87 2.86 21 Ex 2.18 2.7523.5 Th 1.95 2.46
45 D.C-6.10""45*%27%TC 3C/2W 0.158 2510 0.80 2.61 20.5 Ex 2.04 2.5723.5 Th 1.78 2.25
0.193 30601 0.96 3.16 26 Ex 1.94 2.4623.5 Th 2.15 2.72
46 D.W.6.10".45*%27%TC 3W/2C 0.117 1860* 0.59 1.94 77.0 Ex 0.40 0.5124.4 Th 1.27 1.61
0.224 3550 1.12 3.67 25.5 Ex 2.30 2.9123.5 Th 2.50 3.16
47 D.W-6.10".45*.27%PC 3W/2C 0.148 2350 0.68 2.23 20.0 Ex 1.78 2.2523.5 Th 1.52 1.92
* Lowest critical flowrate
t Flowrate of threshold initiating "classic" fluidelastic instability** 3 Core/2 Wing; 3 Wing/2 Core
*** I - U/fD; D - 19.1 mm (0.75 in.)
56
vigorously, but the vibration amplitudes measured up to 10% of diameter
(peak-to-peak) by the available instrumentation were not sufficiently large
to verify tube-to-tube impacting. However somewhere in the range up to the
0.215 m3/s (3400 gal/min) flowrate tested, the response of the tubes (in the
bottom outer window) was considered to become unacceptable with severe tube-
to-baffle impacting almost certain and tube-to-tube impacting likely. One
observation was surprising, while the vibration described above occurred inthe bottom outer window the vibration activity in the top outer window was
relatively minor.
Case 44
Since the test results of Case 43 appeared to be dominated by theresponse of the tubes directly exposed to the nozzle flow, it was decided to
significantly reduce the inlet and outlet nozzle flow velocities (for any
given flowrate) by replacing the nominal size 10-inch with 14-inch diameter
nozzles for this subsequent otherwise unchanged test configuration
designated Case 44. Again, upon flow testing there was high-frequency
response of the tubes under the nozzle, but the amplitudes were smaller than
those during the previous Case 43 Lests. Again, the amplitudes of the
3-span tubes in the outer windows rose gradually with flowrate and withoutany abrupt initiation into instability. As discussed herein, this behavior
presents considerable difficulty to define the threshold flowrate of
unacceptable vibration performance because it does not necessarily coincide
with the onset of local fluidelastic instabilities. For the Case 44
configuration the critical flowrate will be tentatively set at 0.158 m3/s
(2500 gal/min), because upon with an additional 0.008 m3/s (120 gal/min) of
flow an instrumented tube in the bottom outer window more than doubled its
amplitude; however no tube-to-tube collisions could be verified. At higherflowrates most of the tubes in the bottom outer window were vibrating
vigorously with severe tube-to-baffle impacting almost certain and tube-to-
tube collisions very likely but not proven at 0.192 m3/s (3050 gal/min). In
the top outer window there was a noticeable increase of vibration activityof the tubes in the "corner" region formed by the shell periphery and the
edge of the core baffle and along this edge at a flowrate of 0.221 m3/s
(3500 gal/min); otherwise there was no significant activity there.
Case 45
The 10-inch nozzles were reinstalled and the tube bundle rotated 90.
Thus Case 45 provided a 450 layout, 10-in. nozzle, 6-crosspass, double
segmental (3 core/2 wing) baffle, transverse baffle cut configuration.
Since one of each pair of the outer windows is next to the inlet/outlet
nozzles, these near outer windows can be expected to draw more than half of
the flow. Indeed, during flow testing only tubes in the near outer windows
were excited to major vibration responses. As during previous tests with
the 45 layout, the tube vibration amplitudes rose gradually with
flowrate. While well defined single-peak frequency respond data were
obtained at lower flowrates, it was at about 0.158 m3/s (2510 ga../min) when
57
a number of tubes in the near outer window reached an initial peak. At that
flowrate, to be tentatively designated the critical flowrate, the largest
peak-to-peak amplitude measured was 13% of diameter. As the flowrate was
further increased, the amplitudes reduced with the dip bottoming in the
vicinity of 0.173 m3/s (2750 gal/min); subsequently the amplitudes rose
again with flowrate. Fluidelastic instability with tube-to-tube collisions
initiated in the group of tubes directly next to the nozzle at 0.186 m3/s
(2950 gal/min), this instability occurred in spurts and became steady as the
flowrate was further increased to 0.196 m3/s (3100 gal/min).
Case 46
This test case had a 450 rotated square layout, 10-inch nozzle, 6-
crosspass, double-segmental (3 wing/2 core) baffle, transverse baffle cut
configuration. This arrangement locates the 3-span tubes in the central
baffle window and the 4-span tubes in the outer baffle windows, with the
short spans in the end zones. Flow testing indicated local instabilities as
manifested by sharply tuned frequency responses of the 4-span tubes exposed
to the inlet nozzles at moderate flowrates. An instrumented tube in the
front row had amplitudes too small to cause tube collision but with
acceleration levels, e.g. 20 g single amplitude with 77 Hz at 0.117 m3/s
(1860 gal/min), sufficiently high to cause concern for long term wear at the
baffles and tentatively identified as the lowest critical flowrate. Further
increases in flowrate resulted in a slight vibration reduction in the
0.126 m3/s (2000 gal/min) range prior to further rise when most of the front
outer window tubes were observed to buzz strongly at about 0.151 m3/s
(2400 gal/min) with the tube bundle becoming quite noisy at 0.180 m3/s(2850 gal/min). An audible fluidelastic instability began in the central
window at 0.224 m3/s (3550 gal/min) in the central portion of the rows of 3-
span tubes next to the edges of the nearest "wing" baffle. The tubes at the
opposite (far) side of the central window were not thus excited up to the
0.255 m3/s (4040 gal/min) flowrate applied. The power spectral density
curves of many signals indicated presence of frequency contributions in the
70-120 Hz range that appeared to be proportional to flowrate. While not of
immediate practical importance, this phenomenon is of academic interest
because it promises to provide important insights contributing towards the
analyses.
Case 47
Subsequently the tube bundle was rotated by 90* to provide a 450rotated square layout, 10-inch nozzle, 6-crosspass, double-segmental (3
wing/2 core) baffle, parallel baffle cut configuration. This arrangement
locates the least supported 3-span tubes in the central baffle window
directly in the path of the nozzles. Upon testing the instability initiatedin a few of the central window tubes closest to the nozzles at 0.148 m3/s
(2350 gal/min); at 0.153 m3/s (2420 gal/min) the region of instability
extended about 4 rows deep into the bundle. Tube-to-tube impacting could
nor be verified at these flowrates, but did initiate upon further flow
58
increase, probably at 0.160 m3/s (2540 gal/min). At 0.177 m3/s
(2810 gal/min) instability type action extended more than 9 tube rows deep
into the bundle in the central window. While no significant vibrations were
observed in the outer windows, one of the instrumented tubes located there
next to the top core baffle edge indicated strong impacts - probably againstbaffle holes - at the high flowrates.
Discussion
The two principal vibration response phenomena, the lowest critical
flowrate and the threshold of a "classic" fluidelastic instability are
distinctly and separately presented on Table 11 for all double-segmental
baffled tests. In almost every case, the lowest critical flowrate is
determined by localized high flow velocity, created by inherent flow
maldistributions in the end zones. The resulting vibration problems are not
unexpected. An experienced designer would provide additional tube support
in the end zones in order that his design is not limited by end zone flow
conditions and can realize the full benefit of the double-segmental baffle
arrangement in the central baffle spaces. The lowest critical flowrates arepresented here to caution the investigator who may be scanning and comparing
various single- and double-segmentally baffled design options on his
computer terminal.
The interpretation of these localized flow dependent test data is
somewhat subjective, because at this time there are no general acceptance
criteria for unacceptable vibration performance, not to mention for the
damage potential. The problem is discussed in detail in Section V.
On the other hand, the threshold of "classic" fluidelastic instability,
usually indicated by violent tube-to-tube collision, is much more clearly
defined and permits a more meaningful comparison of the test resultsoccurring in the interior of the tube layout. This threshold provides a
fair indication of tube response in the central baffle spaces.
Comparison of the "classic" instability threshold indicates that the
critical (computer generated) gap flow velocities are about the same for
both 3 core/2 wing baffle cut orientations and are about 10% higher for the30* (Cases 39 and 40) than the 450 (Cases 43 and 45) layout pattern
(Table 11). For the 3 wing/2 core transverse-to-nozzle axes baffle cut
configurations, the 30* and 450 layout patterns (Cases 41 and 46), the
threshold velocities are about the same; the parallel baffle cut bundleorientations (Cases 42 and 47) permit no conclusion, this latter baffle
arrangement is not of practical importance, because it involves direct
impingement of the nozzle flow on the least supported 3-span tubes. For
such direct exposure to nozzle flow, the maximum bundle entrance velocity
may provide a better criteria than the gap flow velocity given.
Since the flow splits in double-segmental geometries, the flowrate
before vibration is observed would be expected to be much higher than for
59
segmental baffled geometries. However, in practice this idealized situationis not realized in double-segmental geometries unless special features are
provided to improve the inherent flow maldistributions. The reason is that
when entering or leaving the tube bundle much more than the idealized 50% of
the flow short-circuits the first and last end zones because of the reduced
resistance provided by the close proximity of the flow-turnaround windows to
the nozzle attachment. While this short cut is not available in the
transverse baffle cut, wing baffle near nozzle configuration (e.g. Cases 41
and 46), in that arrangement the total flow confronts the first tube rowencountered in the central window after being forced around the first wing
baffle.
This next discussion is limited to configurations with transverse
baffle cut orientation. The single-segmental baffled tests indicated that
the instability threshold velocity is about 20% higher for the 300 than the
450 layout pattern. Making the not fully defendable assumption of
equivalent tube energization for the double-segmental baffled bundles andapplying a cursory and elementary analysis yield the following results. For
the 3 wing/2 core baffle bundles (Cases 41 and 46) with about equalthreshold velocities, the 30* bundle has about 20% more effective flow
velocity over the tubes adjacent to the near nozzle edge of the first wing
baffle than the 450 bundle. For the 3 core/2 wing baffle configurations the
corresponding ratio is only 10% as a good portion of the flow bypasses the
end zones. Nevertheless, the ratio of corresponding near to far baffle edge
velocities may be the same or larger than for the 3 wing/2 core baffle
bundle. In summary, this indicates that the flow penetrates the 450 bundles
more readily than the 30 , particularly for the 3 wing/2 core baffle
arrangement, as can be expected.
The various vibration response phenomena were not as well defined in
the 450 as in 30 layout bundles. Maximum gap velocities are perpendicular
to the principal flow direction for 300 layouts while they are on the
diagonals for 450 layouts. Also, the 450 bundle is more susceptible to
short cut flows through straight gap lanes between tube rows near the
exterior of bundle. Pressure drop for double-segmental baffled bundles was
well below that for comparable bundles with single-segmental baffles. Other
circumstances often determine the lowest critical flowrates and the
"classic" instability thresholds are not practically achieved. It takes
computer programs such as Refs. 12 or 13 to compare the thermal and
hydraulic performance of single- versus double-segmental baffled bundle and
analyze the designs to ensure that there are no anticipated tube vibration
problems.
The Case 40 configuration tests demonstrated the excitation of 3-span
tubes to higher than fundamental mode frequency tubes. Here, when the flow
short-circuited the first and last baffles and exposed the first and third
span without a major change of direction, there was a tendency to favor the
excitation of the second mode frequency, at least until an instability was
triggered and the frequency was shifted downward towards the fundamental.
60
E. Simulated U-Tube Configuration (Case 48)
The test exchanger was assembled to provide a simulated U-tube configu-
ration to investigate the effect of flexible, low frequency U-bend ends
situated in stagnant water on the overall vibration response of the U-tubespans exposed to shellside flow. Figures 14 and 15 show how this was
implemented with the available straight tubes of the test exchanger. The
flow entering the exchanger was routed through four .crosspasses before
exiting from a central port. The remainder of the exchanger contained
stagnant water that, except for hardware clearances, was separated from the
active flow by a full circular baffle. With no additional supports in the
stagnant water region, the long spans of the tubes simulate U-bend ends.
These long spans are dominant in determining the lowest fundamental natural
frequencies, which are about 20 Hz and differ slightly for the 3-, 4-, and
5-span tube support configurations indicated on Fig. 15. The first three
theoretical modes for the 3-span tubes are shown on Fig. 16. A 300
triangular tube layout pattern and 10-inch size nozzles were used. Thenatural frequencies of a few selected tubes were determined in air and in
water. The critical flow data are included on Table 8 as the four active
crosspasses had the same size as those of the 7-crosspass configurations.
The flowtest results appeared to be consistent with analytical
relationships expressed by Eq. 2, which determine the vibration response by
the combined reinforcing effect of mode shape and velocity distribution,
calculated locally and summed across the length of the tube. Application of
this theory to the subject test means that response at a higher vibration
mode with relatively large amplitudes in the active flow region and a good
"match" with flow velocity can be excited in preference to the low
frequency, fundamental mode with relatively moderate amplitudes in the
active region and a large amplitude rendered ineffective in the zero-flow
stagnant region.
For example, upon flow testing a 3-span tube in the far window vibrated
at the lowest natural frequency until the initiation of a strong instability
shifted the frequency to a higher mode frequency having relatively larger
amplitudes in the active flow area over the two shorter spans (Fig. 15).
Instrumented 4-span tubes in the first three rows under the nozzle indicated
the most significant vibrations occurred at the frequencies of higher modes,
usually 100 Hz and above. Also, instrumentation located in the long span in
the stagnant water region at near midspan, the spot most sensitive to low
frequency first mode excitation, indicated no substantial vibration of any
of the instrumented 3-, 4-, or 5-span tubes.
With the above results, the basic objectives of the test have been met;
however the analysis of the detail data was more difficult.
During the first flow tests an instrumented 3-span tube in the central
part of the far window next to the baffle edge indicated a sharp peaking of
the first mode frequency response at 0.182 m3/s (2880 gal/min), considered
61
to be the lowest critical flowrate. Amplitudes gradually increased with
flowrate until after operating a while at 0.198 m3/s (3140 gal/min) the
frequency shifted abruptly from 22 to 32 Hz, apparently initiating a secondmode vibration having relatively larger amplitudes in the active flow
area. During two subsequent trials this shift occurred at 0.202 m3/s
(3200 gal/min). Upon flow reduction the instability ceased at flowrates as
low as 0.164 m3/s (2600 gal/min) when the frequency shifted down from 28 to23 Hz.
During a second test date "jumping" of tubes and a strong increase ofnoise were observed at 0.200 m3/s (3170 gal/min); however, the
instrumentation relocated in another tube did not initiate severe impacting
and a frequency shift from 22 to 40 Hz until 0.218 m3 /s (3450 gal/min) was
reached.
As already reported, the 4-span tubes under the nozzle in the near
window responded with various higher mode frequencies, felt by finger touch
as a buzzing that eventually extended 4 to 6 rows into the bundle. Analysis
of the instrumented tubes indicated that a frequency of about 100 Hz was
prominent, with various other, higher frequencies contributing and all
switching back and forth in magnitude as the flowrates were changed. At
0.197 m3/s (3130 gal/min) an instrumented tube in the first row right under
the nozzle initiated an abrupt instability increase resulting in
accelerations of 40 g single amplitude at 101 Hz. Due to the severe
vibration in the front rows, flowrates were limited to 0.220 m3/s
(3480 gal/min).
The Case 48 data on Table 8 indicate that evaluation at second mode
vibration provides instability criteria that fall into the same range as
those obtained from the conventional configurations. In summary, from this
test it can be concluded that the "U-bend" in the stagnant flow region can
be neglected in making a rough check for vibration problems. It materially
influenced the value of the lowest natural frequency which did not vibrate
significantly for this flow arrangement. When the shellside fluid is a
liquid, the use of a full baffle at the tangent point of the U-bend appearsto be effective in preventing vibration problems associated with the
U-bend. This may not be the same when the shellside fluid is a gas.
V. PRELIMINARY EVALUATION
The application of flow-induced vibration criteria generally requires
knowledge of the structural details of the exchanger and of various
parameters such as flow velocity, damping and the virtual mass of the
tubes. Even though this report presents a comprehensive description of theheat exchanger structure there are still unknowns because of complexities
associated with the tubes not being perfectly straight, relatively smalltube/baffle hole clearances, the very large number of tube/baffle
interfaces, and misalignment of baffles. The problem of defining a
62
I
I
Fig. 14. Tube bundle of simulated U-tube test. ANL Neg. No. 113-85-2.
i.
'.rr: i'yr
,in.'s.
of a "'
BAFFLESPACING
(T YR)
OBSERVATIONPORT (TYP)
63
3.58m(I4Q75in) TUBE LENGTH INSIDE SHELL5 SPAN TUBE
4 SPAN TUBE
3 SPAN TUBE
- 1!r -- n
' n I h II" ~ - - - I - __- --4k
INLET OUTLET
0.59m (23.25in.) SHELLINSIDE DIAMETER
Fig. 15. Test exchanger in simulated U-tube test configuration (Case 48)
3 SPANS (2/7. 2/7, 3/7)
NoFlow
MODE
1
2
3\Y/f
Fig. 16. Mode shapes of 3-span simulated U-tube
v v
ILI
ZN. ,/ i1
LU
11I
i I .
64
representative flow velocity has been discussed (Section III.C.2). Thereduced (nondimensional) critical flow velocities presented on Tables 6, e
and 11 and the evaluation presented further below are based on the lowest
critical flowrates encountered with increasing flow; however, the
"hysteresis" effects as exemplified by the cessation flowrates (the
declining flowrate at which vibration ceases) indicate that a "safety
factor" may have to be considered to avoid initiation of instability as a
consequence of transients (e.g., startup) at operation with nominal below-
critical flowrates. The determination and use of damping and virtual mass
requires discretion. In the past, both in-air and in-water values have been
used, sometimes separately and sometimes in combination. While the majority
of the investigators have used in-water values, Chen [7] has recently
proposed the use of in-air values as a means to avoid the ambiguity of which
coupled mode frequency and associated added mass coefficient to use. In the
following, the in-water parameters are utilized.
The difficulties of determining damping have been discussed widely in
the literature. For the purpose of calculations herein, the fraction of
critical damping C will be taken to be 0.035 in water, unchanged from the
high and thus conservative value proposed previously [1]. The value of the
virtual mass was recomputed on the basis of data presented in Table 12 and
discussed below. The added mass correction factor [20], required to compute
in-water natural frequency and mass-damping parameter, is a function of the
array pattern, the size of the array considered, and the pitch-to-diameter
ratio. In effect, there is a different added mass factor corresponding to
each of the coupled modes. Ideally, one should use the added mass factor
corresponding to the particular mode in which the bundle goes unstable.
Unfortunately, the instability mode is, in general, not known. As a
compromise, the added mass correction factor is calculated with in-water
parameters for the uncoupled vibration mode which takes into account the
proximity to surrounding tubes in the tube bundle but does not account for
coupling with adjacent tubes (adjacent tubes are assumed to be rigid). It
should be noted that these results are for a tube in the center of an array,
and thus are not truly applicable for tubes on the periphery of the tube
bundle. The virtual mass is obtained by multiplying the added mass
coefficient by the mass of the displaced water and adding the mass of the
tube. The square root of the actual over virtual mass ratio defines the
reduction of the natural frequency in water compared to in air. Values of
the mass-damping parameter calculated with in-water parameters, corre-
sponding to the uncoupled mode, are given in Table 12. This table also
presents the first mode theoretical in-air and in-water (uncoupled mode)
frequencies, a comparison w.th the experimental tube vibration frequencies
is presented on Tables 6, 8, and 11.
As discussed in Section II.B, Connors' [6] correlation expressed by
Eq. 1 will be employed for this preliminary evaluation. As applied here,
the test data were inserted in Eq. 1 to determine the instability threshold
constant 0. The crossflow velocities were generated from the measured
65
Table 12. Virtual mass and natural frequency calculation
Layout
Tube type
Tube diameter, mmin.
Pitch/dia. ratio
Added mass coefficient
(uncoupled mode)
Array size
Tube mass, mact, kg/mlb/in.
300 and 600 900 and 450
30* and 60*triangular
Plain
19.10.750
1.25
1.71
37
0.5970.0335
90 and 45*
square
Plain
19.10.750
1.25
1.52
25
0.5970.0 335
Displaced water,actual mass kg/m
lb/in.
Virtual mass, mv, kg/mlb/in.
Ratio: (m /m )0.5act v
Mass-damping parameter, 6mIn-water (; = 0.035)
Theoretical fundamental(1st mode) natural frequencies
6-crosspasses, 3-span tube, Hz4-span tube, Hz6-span tube, Hz
7-crosspasses, 4-span tube, Hz
Simulated U-tube, 3-span tube,2nd mode frequency,
0.2850.0160
1.090.0609
0.742
0.659
In water
22.9
23.877.2
29.9
19.634.4
0.2850.0160
1.030.0578
0.761
0.626
In water
23.524.479.1
30.7
In air
30.9
32.1104.0
40.4
26.546.4
HzHz
66
flowrates with the aid of the HTRI computer program. The mean gap flow
velocities for the 450 and 600 layouts were obtained by multiplying the
crossflow velocities parallel to the principal flow direction by factors of
1.54 and 2.33, respectively. As shown on Tables 6, 8, and 11, each reduced
flow velocity was computed twice: first, using the actual experimental
frequency and secondly, using the computed theoretical frequency, because
this is the one available to the designer. The values of s obtained are
considered to be low and conservative, because input values ; and UCR were
taken to be on the high and low side, respectively.
It is pointed out that all critical f lowratc presented are not
directly comparable, because they may be associated with different
instability phenomena. For instance, the critical flowrate causing
unacceptable vibration of the front row tubes due to end zone flow
conditions may be substantially reduced by lowering inlet velocities with
larger nozzle, while a critical flowrate initiating a classic instability in
the interior of the bundle is not as much influenced by nozzle size. This
indicates the advisability of alternate calculation, utilizing in the
example cited, for instance, the nozzle inlet flow velocity as the insta-
bility parameter. Furthermore, since the front tubes tend to be excited to
higher frequencies, vibration with moderate displacement amplitudes result
in substantially higher acceleration with consequently larger impact and/or
wear damage potential.
It is also noted that the results presented apply to the specific
configurations tested and that the results can be expected to be influenced
by changes in parameters such as pitch-to-diameter ratio, baffle clearance,
baffle width, etc. To provide a comparison with results of previous tests,
Table 13 lists groups of corresponding test cases to facilitate comparison
with respect to the four groups of different parameters listed: layout,
number of crosspasses, and single- and double-segmental baffles. The
grouped data readily permit the computations of data ratios; it is
anticipated that these ratios and the factors that influence them will be
more closely investigated under this program in the future.
VI. PRESSURE DROP MEASUREMENTS
A. Test Procedure
Shellside pressure drop measurements were taken for all configurations
tested with room temperature water as the shellside fluid. Figure 17
schematically shows the location of the pressure taps on the shell and
nozzles for the 9 different connection set-ups used during the 22 tests
covered herein. Figure 18a and b shows details of the size and locations of
the pressure taps A and I in the inlet and outlet nozzles. The inlet
connection (left center of photo ou Fig. 1) provides more than 12 diameters
of straight pipe to reduce extraneous prior-to-entrance effects. Both
67
Table 13. Comparison of groups of corresponding test configurations
Varying parameters: Layout, number of crosspasses, single- and double-segmental baffles.
Computed Theoretical Instability PressureCritical Gap Flow Vibration Reduced Threshold Drop at
Case Configuration Code Flowrate Velocity,U Frequency,f Velocity Constant 1000 g9mNo. Varying parameter underlined gal/min m/s ft/s Hz U a lb/in.
6 F.P.6.14".30.29%TC 1980 1.33 4.37 22.9 3.05 3.76 3.3832 F.P.6.14".60%.30%TC 1840 1.08 3.55 22.9 2.48 3.05 2.9619 F.P.6.14"*90.30%TC 1600 1.17 3.83 23.5 2.61 3.30 2.5329 F.P.6.14""45*"30%TC 1970 1.03 3.38 23.5 2.30 2.91 2.30
21401 1.11 3.65 23.5 2.49 3.14
3 F.P.8.10".30'e26%TC 3130 2.55 8.35 37.2 3.59 4.42 6.0135 F.P-7.10".30.29%TC 2720 2.05 6.71 29.9 3.59 4.42 4.55
7 F.P.6.10".30 .29%TC 1970 1.33 4.35 22.9 3.04 3.74 3.99
16 F.P.8.10""90 "26%TC 2340 2.12 6.95 38.1 2.92 3.69 4.6237 F.P"7.10".90*%30%TC 2270 1.76 5.79 30.7 3.02 3.81 3.5120 F.P.6.10" 90*.30%TC 1650 1.20 3.95 23.5 2.69 3.40 2.77
7 F.P.6.10".30*.29%TC 1970 1.33 4.35 22.9 3.04 3.74 3.9940 DC-6-10" 30-25%TC 1830 0.79 2.58 22.9 1.80 2.22 2.13
24501 1.05 3.45 22.9 2.41 2.9741 D.W.6.10".30*.25%TC 2590 1.10 3.62 22.9 2.53 3.12 2.07
29 F.P6.14""45*%30%TC 1970 1.03 3.38 23.5 2.30 2.91 2.3021401 1.11 3.65 23.5 2.49 3.14
45 D.C6.10""45*.27%TC 2510 0.80 2.61 23.5 1.78 2.25 1.4830601 0.96 3.16 23.5 2.15 2.72
46 D.W-6.10".45*%27%TC 1860 0.59 1.94 24.4 1.27 1.61 1.483550 1.12 3.67 23.5 2.50 3.16
t Threshold initiating "classic" fluidelastic instability above lowest critical flowrate
tt See Table 3
ttt U - U/fD; D - 19.1 mm (0.75 in.)
I gal/min 6.309 x 10-5 m3/sI lb/in. 2
- 6.895 kPa
68
E G H1 TV 1
42?F
a) 6-crosspass, transverseCases 27 to 32 and 34
baffle cut configuration.
B C E G H
iTS I I II I I I
I I I0
n II
I (b \ 1
Tap:C:E:
z/L0.250.500.75
b) 6-crosspass, parallel baffle cut configuration.
B
A
D
C F
C I
H
Tap: z/LC: 0.291): 0.50F: 0.50G: 0.71
c) 7 crosspass, transverse baffle cutCases 35 and 37
configuration.
Fig. 17. Location of pressure taps
BC
I0A D LjJ
Tap:C:D:"
B:F:G:
z/L0.170.330.500.670.83
Case 33
I
. T ..
69
E
N~
1 1 ! 1.
D F
G fI
iH
Tap: z/LC: 0.25D: 0.33E: 0.50F: 0.67C: 0.75
d) 7-crosspass, parallelCases 36 and 38
baffle cut configuration.
B K
A D E F
C C
(Do I CO)
Tap:C:D:
E:
K:F:C:
z/L0.170.330.500.500.670.83
e) Double-segmentA, 3 core/2 wing baffles,parallel cut configuration.Cases 39, 43, and 44
BC K C H
tA 4+
D F
4 !.. IT
Tap:C:D:
E:
K:F:C:
z/L0.170.330.500.500.670.83
f) Double-segmental, 3 wing/2 core baffles,transverse cut configuration.Cases 40 and 45
Fig. 17. Location of pressure taps (Contd.)
B C
A
L c1 f\IIt 11 I "j
T
I
70
B K
- I1 I
A D E F
C G
OI OI IO
H
Tap:C:D:
E:
K:F:G:
g) Double-segmental, 3 wing/2 core baffles,transverse cut configuration.Cases 41 and 46
BC K G H
0 0
A E I
D F
I00
Tap:C:D:"
E:
K:F:G:
h) Double-segmental, 3 wing/2 core baffles,parallel cut configuration.Cases 42 and 47
B C D HT r
KTp . RFa1p
A EF G i I
i) Simulated U-tube configuration. Case 48
Tap:C:
F:G:H:K:
Fig. 17. Location of pressure taps (Contd.)
z/L0.170.330.500.500.67.0.83
z;L0.110.330.500.500.67.0.83
z /L0.170.250.250.290.330.500.93
I
71
.- 2zSELLINSIDE RADIUS
3 3 7 D IA . _ _ _3 2
H327-19 DIA.
COUPL ING
TO NMOUT TAP(a) 14-INCH NOZZLE
PIPE INSERT
473+_ 241 DIA.
4.8 DIA.-29
TAP
(b) 10-INCH NOZZLE
WINDOWS
335 DIA.
TAP SAME AS14-INCH NOZZLE
(c) CENTRAL TAP INOBSERVATION PORT
DINENSIONS IN m
Fig. 18. Details of nozzles and pressure tap locations
72
nozzles were of the same nominal 14-inch diameter pipe size. The nominal
10-inch size was provided by placing inserts into both the inlet (main-
taining a long approach) and outlet steel pipe (Fig. 18b). The central
observation ports, built to serve as nozzles for special tests such as the
simulated U-tube test and for future testing, have essentially the same
construction as the inlet/outlet nozzles. The windows are contoured with
transparent acrylic plastic to provide a continuous surface at the internal
shell diameter. Figure 18c indicates the sheltered location of the central
tap E, to which pressure is transmitted through a narrow annular gap around
the periphery of the window insert.
The overall inlet to outlet pressure drop was measured between the taps
designated A and I by means of a differential pressure transducer. The
transducer usually employed for this program had a 690 kPa (100 lb/in.2 )
differential pressure range. The signal output was obtained by means of a
bridge conditioner, routed through a resistance-capacitance network to
attenuate signal fluctuations, and displayed on a digital voltmeter. The
system is calibrated end-to-end. The pressure level of the exchanger outlet
was measured also, and it usually remained at less than 240 kPa (35 lb/in.2 )
above atmospheric.
B. Overall Pressure Drop
When the overall pressure drop Ap (taps A to I) is plotted as a
function of flowrate Q on log-log paper, the data can be correlated with a
straight line. This implies that the overall pressure drop can be
correlated by a power function relationship of the general form
Op = yQ (3)
where y and a are constants for a particular tube bundle configuration.
In this report the above equation will be expressed with US units as
Ap(lb/in. 2 ) = y(lb/in. 2 ) 1Q(gallmin) a (4)1000 1
or, with SI units
Ap(kPa) = y(kPa) Q(m3 (5)p {10.0 6309}
which, taking logarithms on both sides becomes
73
in Ap(lb/in.2) = Rn y(lb/in.2) + a i 1Q(gal/min)} , (6)1000 1
or,
in Ap(kPa) = In y(kPa) + a in 006309 (7)
For the pressure drop data obtained from each of the various test configura-
tions, Eq. (6) was employed to determine the constants y and a by means of
linear regression analysis. Table 14 indicates the range of flowrates from
which the data were taken, summarizes the results of the linear regression
analysis computations, and lists the constants a and y. To facilitate
comparison with previous tests, pressure drop y has been also included on
Table 13.
C. Pressure Distribution
The pressure distribution through various sections of the test
exchanger was determined by taking pressure drop measurements between taps B
through H or K and the outlet tap I of the exchanger with the differential
pressure transducer (Fig. 17). The connections were made by switching with
a valve system.
To determine the normalized fractional distribution, the overall
pressure drop was set equal to unity and the fractional drops (remaining to
the outlet tap) were calculated for each flowrate tested and averaged. The
data are listed on Table 15.
D. Analysis
Comparison of the pressure drop across the full tube bundle, 29% or 30%
baffle cut configurations, indicates that the drop across the 600 and 450
layout bundles is about 10% less than across the corresponding 300 and 900
bundles (Table 13). A probable contributing factor is the maximum mean gap
crossflow velocity through the gap between the tubes. When computed with
very much idealized assumptions (e.g., pure and uniform crossflow in the
plane of the paper of Figs. 4, 6, 10, and 12), for a given flowrate the
maximum mean gap flow velocities are the same for 300 and 900 layouts, but
reduced to 87% and 71% in corresponding 600 and 450 layouts for a 1.25
pitch-to-diameter ratio. This may explain why a 450 layout with a seemingly
more arduous flowpath has a smaller pressure drop than a 900 bundle.
The double segmental baffle test data indicate that, in comparison to
single segmental test, the overall pressure drop is substantially reduced
and that a larger fraction of the drop occurs in the entrance and exit
regions. Examination of instability data on Table 13 shows that on a
pressure drop basis the double segmental bundles perform well with respect
to vibration.
74
Table 14. Overall pressure drop versus flowrate0p - y(Q/1000)a with U.S. units indicated in Eq. 4*
Overall pressureRange of flowrates drop Ap at
Q used to 1000 gpm 2000 gpmConfiguration determine a and y Exponent y
Case code** gal/min a lb/in.2 lb/in.2
27 F.P.6.14""45*.16%eTC 790-2760 1.98 5.67 22.328 N.P.6.14".45*.16%TC 800-2800 1.95 3.29 12.729 F.P.6.14".45*.30%TC 800-2400 1.91 2.30 8.6830 F.P-6.14""60*.16%TC 790-2200 1.94 6.59 25.231 N.P"6.14".60*.16%TC 850-2990 1.91 3.33 12.532 F.P.6.14".60*%30%TC 1050-2490 1.90 2.96 11.133 F.P.6.14""60*"30%PC 690-2160 1.85 2.92 10.534 N.P.6.14".60*%30%TC 810-3220 1.81 1.17 4.0935 F.P.7.10""30*929%TC 800-2720 1.89 4.55 16.836 F.P.7.10".30*.29%PC 740-2610 1.88 4.34 16.037 F.P.7.10""90* 30%TC 790-2320 1.89 3.51 13.038 F.P.7.10""90 0 30%PC 690-2490 1.88 3.22 11.939 D.C6.10""30* 25%PC 970-2990 1.90 2.05 7.6840 D.C-6.10".30*.25%TC 1000-2280 1.91 2.13 8.0041 D.W.6.10".30 .25%TC 970-3100 1.89 2.07 7.6442 D.W.6.10""300.25%PC 700-2600 1.92 2.00 7.5743 D.C.6.10""45*.27%PC 590-3010 1.93 1.44 5.4744 D.C.6.14".45*.27%PC 800-3460 1.95 1.11 4.3045 D.C.6.10""45*.27%TC 760-3010 2.00 1.48 5.9346 D.W.6.10".45*"27%TC 600-3660 1.92 1.48 5.6247 D.W-6.10".45*.27%PC 700-3060 1.92 1.49 5.6348 U.P.4.10".30'%29%TC 730-3230 1.92 3.12 11.8
* 1 gal/min (gpm) = 6.309 x
1 lb/in.2 - 6.895 kPa
10-5 m3/s
** See Table 3
75
VII. CLOSING REMARKS
This investigation is motivated by the need to obtain tube vibration
data from industrial heat exchanger configurations, as well as from field
experiences, to contribute to the improvement of existing prediction methods
for avoiding vibration damage. Previous test reports [1-3] have discussed
the complexities of both the structural and the fluid dynamic phenomena
encountered in investigating heat exchanger tube vibrations.
This report covers the testing of 22 different tube bundles,
supplementing the previously reported tests of 25 configurations, all
representing different combinations of tube layout, number of crosspasses,
baffle type and orientation, nozzle size, etc. The basic data are tabulated
and organized in such a way that they can be used by future researchers to
apply to the then state-of-the-art vibration prediction methods. An
available tube instability prediction method, based on a three-dimensionalflow distribution code, has been applied to several basic single-segmental
baffled bundle configurations tested previously [12]. Upon comparison, the
test results appear to be consistent with these analytical relationships
that determine the vibration response by the combined reinforcing effect of
vibration mode shape and flow velocity distribution. Section III.F of this
report outlines the need for criteria to define the limits of acceptable
vibration response.
The generated pressure drop data are expected to be useful for the
improvement of computer programs for industrial heat exchanger design. The
tests are part of a Heat Exchanger Tube Vibration program that also includes
the collection of well documented field experience cases that point out
those configurations most likely to experience vibration problems and are
published in an annually updated data bank [21].
ACKNOWLEDGMENTS
This work was performed as part of a Heat Exchanger Tube Vibration
Program which is sponsored by the U.S. Department of Energy, Office of
Energy Utilization Research, under the Energy Conversion and Utilization
Technologies (ECUT) Program, and represents a U.S. contribution to theInternational Energy Agency (IEA) Program of Research and Development on
Energy Conservation in Heat Transfer and Heat Exchangers. Heat TransferResearch, Inc. (HTRI), an applications oriented research organization,
provided consultation, cooperation, and assistance to the program. The
continuing encouragement and support of M. E. Gunn, W. H. Thielbahr, and J.
J. Eberhardt of the US/DOE and J. Taborek of HTRI are gratefully
appreciated.
We also thank R. K. Smith for his assistance with the setup and conduct
of the tests.
Table 15. Pressure drop distribution
Listed is the fraction of the pressure drop between the tap indicated and the outlet tap to the overall inlet/outlet
pressure drop.Listed underneath is the fractional pressure drop between taps.
Location of taps is illustrated on diagrams of Fig. 17.
Note: Taps A and I are on bottom of inlet and outlet nozzles.
Taps E and K, if used, are on bottom of central port.Taps B and H are on far (or near) side of shell in horizontal plane of flow directly across from nozzles.
Taps C, D, F, and G usually are on top or on far or near side (with respect to nozzles) of shell. The
distance from the inlet tubesheet is indicated as a fraction of the internal shell length, L, on Fig. 17.
Case 48: some exceptions apply.
Configuration TapCase Code A B C D E F G H
27 F.P.6.14" "45*%16ZTC 1 .961 .865 .663 .507 .337 .144 .108.039 .096 .202 .156 .170 .193 .03b
28 N.P.6.14" "45* 16%TC 1 .954 .861 .643 .497 .318 .128 .137.046 .093 .218 .146 .179 .190 -.009
29 F.P.6.14" .45*.30%TC 1 .902 .837 .666 .528 .380 .227 .239.098 .065 .171 .138 .148 .153 -.012
30 F.P.6.14" "60* 16%TC 1 .943 .847 .641 .507 .339 .154 .123.057 .096 .206 .134 .168 .185 .031
31 N.P.6.14".60*%16%TC 1 .935 .839 .629 .492 .31/ .139 .171.065 .096 .210 .137 .175 .178 -. 032
32 F.P.6.14" .60*30ZTC 1 .881 .819 .659 .523 .383 .232 .238.119 .062 .160 .136 .140 .151 -. 006
33 F.P.6.14"60*%30%PC 1 .896 .754 .547 .310 .192.104 .142 .207 .237 .118
34 N.P.6.14""60* 30%TC 1 .893 .852 .662 .518 .354 .185 .209.107 .041 .190 .144 .164 .169 -.024
35 F.P.7.10""30'.29%TC 1 .876 .706 .581 .514 .360 .249.124 .170 .125 .067 .154 .111
36 F.P.7.10""30 "29%PC 1 .889 .785 .656 .540 .432 .303 .206.111 .104 .129 .116 .108 .129 .097
37 F.P.7.10""90*%30%TC 1 .856 .719 .619 .545 .396 .301.144 .137 .100 .074 .149 .095
38 F.P.7.10""90*"30%PC 1 .889 .810 .677 .576 .455 .327 .224.111 .079 .133 .101 .121 .128 .103
Table 15. Pressure drop distribution (Contd.)
Configuration Tap
Case Code* A B C D E K F G H
DeC 6.10""30 *25%PC
D.C.6.10".30 "25%TC
D.W-6.10".30 "25%TC
D.W.6.10""30 25%PC
D.C.6.10" .45* 27%PC
D.C-6.14" "45*-27%PC
D.C.6.10""45*.27%TC
D.W.6. 10" "45*.27%TC
D.We6.10""45 "27%PC
U.P-4.10".30*-29%TC
.199
.186
.204
.177
.169
.153
.122
.174
.150
.801
.814
.796
.823
.831
.847
.878
.826
.850
.807.193
.058
.035
.088
.05Q
.083
.092
.042
.098
.054
.743
.779
.708
.764
.748
.752
.836
.728
.796
.733.074
.076
.067
.055
.073
.058
.069
.075
.044
.097
-. 026
.667
.712
.653
.691
.690
.683
.761
.684
.699
.040
.070
.022
.056
.049
.074
.060
.016
.034
.627
.642
.631
.635
.641
.609
.701
.668
.665
.759 .597.162
.031
.017
.030
.015
.026
.035
.016
.031
.013
.596
.625
.601
.620
.615
.574
.685
.637
.652
.077
.074
.103
.092
.082
.101
.068
.098
.087.333
.040
.519
.551
.498
.528
.533
.473
.617
.539
.565
.094
.079
.098
.067
.094
.116
.079
.091
.072
.425
.472
.400
.461
.439
.357
.538
.448
.493
.011
.006
.007
.029
.010
.018
.006
.015
.025
.414
.466
.393
.432
.429
.339
.532
.433
.468
.557 .543 .383
.014 .160
* Refer to nomenclature or Table 3
39
40
41
42
43
44
45
46
47
48
78
REFERENCES
1. Halle, H., and Wambsganss, M. W., "Tube Vibration in Industrial SizeTest Heat Exchanger," Technical Memorandum ANL-CT-80-18, Mar. 1980,Argonne National Lab., Argonne, IL.
2. Wambsganss, M. W., and Halle, H., "Tube Vibration in Industrial SizeTest Heat Exchanger (300 Triangular Layout - 6-Crosspass Configura-
tion)," Technical Memorandum ANL-CT-81-42, Oct. 1981, Argonne National
Lab., Argonne, IL.
3. Halle, H., and Wambsganss, M. W., "Tube Vibration in Industrial SizeTest Heat Exchanger (900 Square Layout)," ANL-83-10, Feb. 1983, ArgonneNational Lab., Argonne, IL.
4. Halle, H., Chenoweth, J. M., and Wambsganss, M. W., "Flow-Induced TubeVibration Thresholds in Heat Exchangers from Shellside Water Tests,"Symposium on Flow-Induced Vibration; Vol. 3, Vibration in HeatExchangers, ed. M. P. Paidoussis, J. M. Chenoweth and M. D. Bernstein,ASME, New York, 1984, pp. 17-32.
5. Chen, S. S., "Instability Mechanisms and Stability Criteria of a Groupof Circular Cylinders Subjected to Cross Flow. Part I: Theory"; "Part
II: Numerical Results and Discussions"; J. Vibration, Acoustics,Stress and Reliability in Design, Trans. ASME, Part I: Vol. 105, Jan.1983, pp. 51-58; Part II: Vol. 105, Apr. 1983, pp. 253-260.
6. Connors, H. J., Jr., "Fluidelastic Vibration of Tube Arrays Excited byCross Flow," Proceedings of the Symposium on Flow-Induced Vibration in
Heat Exchangers, ASME Winter Annual Meeting, New York, 1970, pp. 42-56.
7. Chen, S. S., "Guidelines for the Instability Flow Velocity of TubeArrays in Crossflow," Journal of Sound and Vibration, Vol. 93, No. 3,1984, pp. 439-455.
8. Pettigrew, M. J., Sylvestre, Y., and Campagna, A. 0., "VibrationAnalysis of Heat Exchanger and Steam Generator Designs," Nucl. Eng.Des., Vol. 48, 1978, pp. 97-115.
9. Standards of Tubular Exchanger Manufacturers Association, Sixth ed.,The Tubular Exchanger Manufacturers Association, Inc., New York, 1978.
10. Wambsganss, M. W., Yang, C. I., and Halle, H., "Fluidelastic Insta-bility in Shell and Tube Heat Exchangers - A Framework for a PredictionMethod," ANL-83-8, Dec. 1982, Argonne National Lab., Argonne, IL.
11. Wambsganss, M. W., Yang, C. I., and Halle, H., "Fluidelastic Insta-bility in Shell and Tube Heat Exchangers - A Framework for a PredictionMethod," Symposium on Flow-Induced Vibration; Vol. 3, Vibration in HeatExchangers, ed. M. P. Paidoussis, J. M. Chenoweth and M. D. Bernstein,
ASME, New York, 1984, pp. 103-118.
79
12. Mulcahy, T. M., Wambsganss, M. W., and Yang, C. I., "Heat ExchangerVibration Analysis (HXVA) for Prediction of Tube Bundle Instabilities,"
Argonne National Laboratory Report ANL-85-40, May 1985.
13. "HTRI ST-4 Computer Program for the Design or Rating of Shell-and TubeHeat Exchangers," 1980, heat Transfer Research, Inc., Alhambra, CA.
14. Palen, J. W., and Taborek, J., "Solution of Shell Side Flow Pressure
Drop and Heat Transfer by Stream Analysis Method," CEP Symp. Ser.,Vol. 65, No. 92, 1969, pp. 53-63.
15. Connors, H. J., Jr., "Fluidelastic Vibration of Heat Exchanger TubeArrays," Trans. ASME, J. of Mechanical Design, Vol. 100, April 1978,pp. 347-353.
16. Halle, H., and Wambsganss, M. W., "Shellside Waterflow Pressure Dropand Distribution in Industrial Size Test Heat Exchanger," ANL-83-9,Jan. 1983, Argonne National Lab., Argonne, IL.
17. Halle, H., Chenoweth, J. M., and Wambsganss, M. W., "ShellsideWaterflow Pressure Drop Distribution Measurements in an Industrial-Sized Test Heat Exchanger," A Reappraisal of Shellside Flow in HeatExchangers, ed. W. J. Marner and J. M. Chenoweth, ASME, New York, 1984,
pp. 37-48.
18. Connors, H. J., "Fluidelastic Vibration of Tube Arrays Excited byNonuniform Cross Flow," PVP-41, Flow-Induced Vibrations of Power PlantComponents, ASME, 1980, pp. 93-107.
19. Kissel, J. H., "Flow Induced Vibration in Heat Exchanger wtih SealStrips," Flow-Induced Heat Exchanger Tube ViL'ration - 1980, ed.J. M. Chenoweth and J. R. Stenner, ASME, New York, 1980, pp. 27-33.
20. Chen, S. S., and Chung, H., "Design Guide for Calculating HydrodynamicMass, Part I: Circular Cylindrical Structures," Technical MemorandumANL-CT-76-45, June 1976, Argonne National Lab., Argonne, IL.
21. Halle, H., Chenoweth, J. M., and Wambsganss, M. W., "DOE/ANL/HTRI HeatExchanger Tube Vibration Data Bank," Technical Memorandum ANL-CT-80-3,Feb. 1980; Addendum 1, Jan. 1981; Addendum 2, Nov. 1981; Addendum 3,Jan. 1983; Addendum 4, Dec. 1983; Addendum 5, Jan. 1985; Addendum 6,Jan. 1986, Argonne National Laboratory, Argonne, IL.
80
APPENDIX
Summary of Sensory Observations: Cases 27-48
The tube bundle was backlighted and sensory (sight, sound, and feel)
observations of tube bundle response were made as the flowrate was
changed. In particular, tube motion was detected by sighting down the bores
of the tubes, or by holding a finger against the tube ends where they come
through the tubesheets. Rattling and impacting were audible and readilydetected by ear. When supported by a short, i.e. one baffle spacing long,
span, the tubes directly in front of the nozzle tended to be excited at
higher mode frequencies, usually between 70 to 140 Hz. This high frequency
excitation could be felt better than seen, and is referred to as
"buzzing." A case-by-case documentation of sensory observations made during
testing is given below. Subsequent evaluation of instrumentation may have
indicated lower flowrates than observed by senses.
Table 3 presents more complete descriptions of the configurations and
the location of principal tube rows that can be used in conjunction with the
schematics on Figs. 4, 6, 10, and 12 to identify the location of individual
tubes.
The flowrates are presented in gallons per minute (gpm), where 1
gal/min = 6.309 x 10~5 m3/s.
Case 27
Full Bundle - 6 Crosspass - 450 Layout - 16% Baffle Cut
Flowrate (gpm) Observation
1190 Quivering felt in far window tubes DD-10, 18, 20, and 22,
EE-11, FF12 and near window tubes D-8, 10, 24, and 25 andC-11
1410 Stronger quiver in tubes DD-8 and 10, otherwise like 1190with additional tubes quivering DD-24 and 26, EE-23,
FF-22, and B-22
1600 Slight vibration felt in tubes DD-8, 10, EE-11, andFF-12, otherwise like 1410. Also felt slight quiver in
some saddled tubes on top of rows E and CC
1800 Tube DD-10 is actively and tubes EE-11, FF-12, D-10, and
B-12 are moderately vibrating. Almost all of far windowtubes and lower tubes in near window are quivering
81
2070 Same as 1800, tubes DD-8, D-8, 24, and 26 are moderately
vibrating. Near window tubes develop high frequency
buzz.
2360 Tube D-8 and 10 vibrate actively. There is moderate
vibration of shell periphery tubes in far window. High
frequency buzz felt in near window, stronger on top.
Quiver also felt with fingers in core region.
2550 Same as 2360, actively vibrating in far window are tubes
DD-8, 10, and 24, EE-11 and 23, FF-12, and GG-15. Tubes
in row D, C-11 to 19, B-12 to 16, and A-15 are buzzing(B-12 and A-15 strongly) while tubes C-21 and 23 and B-20
and 22 vibrate moderately at lower frequencies.
2750 Tubes DD-8 and 10, EE-11, and FF-12 vibrate vigorously,
tubes DD-22 to 26, EE-21 and 23, and FF-22 are active.In upper near window there is high frequency buzz of
tubes Nos. 8 through 18 (very strongly for tubes B-11 and
A-15), while tubes 19 through 26 are Etive at lowerfrequencies. Occurrence of tube-to-tube impacting is not
evident (also not from instrumentation) during thisparticular test run. At the exit end one hears impacting
noises, which are probably caused by tie bar vibration.
3010 Almost all far window tubes are vibrating vigorously if
not impacting.
Case 28
NTIW Bundle - 6 Crosspass - 450 Layout - 16% Baffle Cut
1000 Slight quivering of tube E-27.
1200 Same as 1000, some vibration heard, probably tie bar on
inlet side, but nothing seen in port.
1400 Tube E-27 quivers, slight quivering felt in saddled rowsE and CC. Tie bar vibration as at 1200.
1610 Tube E-27 vibrates slightly. Slight quiver of top andbottom tubes in saddled rows, E-7, CC-7 and 27. Also
quivering are tubes CC-17 and Y-31. Upper tie bar in far
window quivers, lower tie bar vibrates about 1.5 mm
(0.06 in.) peak-to-peak amplitude.
1810 Same as 1610. Additional tubes quivering are D-9 andBB-28. Lower tie bar in far window vibrates 3 mm
(0.12 in.) peak-to-peak.
82
2000 Tubes E-27 and CC-15 vibrate moderately. Tube E-7 and 9,
G-19, CC-7, 9, 11, 13, and 27, BB-14 and 28, AA-15, and
Z-18 are quivering. Tie bars same as 1810 gpm.
2400 Vibration seen or felt in all row CC tubes, also seen in
tubes E-7, 9, 11, and 27. Many tubes rows F through K
and W through BB felt to quiver with hand, also the same
in central region between rows 7 and 27, approximately.In far window, top tie bar vibrates about 2 mm (0.09 in.)
and bottom tie bar 3 mm (0.12 in.) peak-to-peak.
2800 About same as 2400. About 5 mm (0.19 in.) peak to peak
amplitude vibration of top tie bar, bottom tie bar is
shuddering.
3200 Tube E-13 is active, may be unstable. Vibration seen in
tubes CC-7, 9, and 11, E-15 and 27. Tie bars observed to
vibrate irregularly (shudder) with about 6 mm (0.25 in.)
peak-to-peak.
Up to 3600 Some tubes, including H-16, E-13 and 15, rotated and
moved at times toward the inlet end.
Case 29
Full Bundle - 6 Crosspass - 450 Layout - 30% Baffle Cut
800 No significant observation
1000 Very slight quiver in row Y tubes, tube Y-15 can be felt
with fingers.
1100 Quiver seen on tubes in diagonal rows Y-3/DD-8 and
Y-5/FF-12 and tube Z-8, with slightly more activity of
top tubes. Tubes Y-7, 9, 11, and 13 vibrate slightly,
tube Y-15 moderately.
1200 Same as 1100, quiver of remaining row Y tubes and tube
rows below and including tubes Z-22 and AA-23.
1400 Moderate vibration of central far window region tubes
Y-13 to 19, Z-14 to 20, AA-15 to 19, BB-16 and 18.Slight vibration of tubes DD-10, EE-11, and FF-12. Lower
row Y, Z, and AA tubes can be felt distinctly, almost all
other far window tubes can be felt to some extent.
1500 About same as 1400. Near window tubes A-15 and 1-15 arequivering.
83
1600 Central region of slight and moderate vibration in far
window is increasing Y-11 to 23, Z-10 to 24, AA-11 to 23,
BB-12 to 22. Slight to moderate activity along top
diagonal rows Y-3/DD-8 and Y-5/FF-12, also slightly alongbottom diagonal rows Y-29/FF-22 and Y-31/DD-26. Various
tubes in near window can be felt to buzz, particularly inA and B rows.
1830 Central region tubes (see 1600) vibrate actively, tubesin region above these and above GG-15 and EE-12 vibrate
moderately. Lower region tubes are relatively quiet, but
slight vibration there can be felt with finger. Tubes innear window are buzzing slightly. Lower tie bar in far
window vibrating about 2.5 mm (0.1 in.) peak-to-peak.
1990 Strong vibration if not impacting of the tubes in the
region defined (enclosed) by Y-7/Y-23/AA-23/BB-22/CC-19/
CC-7/Y-7. Tubes in to? diagonal rows are active.
2000 Pronounced increase in activity, more tubes impacting in
central region (see 1990), tubes Y-13 and 15 rotate
somewhat, but seem to hold afterward. Slight vibration
in two lower-diagonal tube rows and in lower row EE, FF,
and GG tubes. More near window tubes are buzzing.
Case 30
Full Bundle - 6 Crosspass - 60 Layout - 16% Baffle Cut
800 No significant observation
1020 Slight quiver of tubes PP-10, 16, 20, and 22; QQ-11, 13,and 15, RR-16; TT-16, and 00-21.
1220 As before, in addition PP-6 and 8 and QQ-9 are slightly
quivering.
1370 Most far window tubes in rows PP, QQ, and RR arequivering. Tube in central region of near window quiver
slightly.
1600 Most of far window tubes quiver or vibrate moderately.Tubes SS-11, TT-10 and 12; and UU-13 are quiet. In near
window shell periphery tubes B-10 and 18; C-9 and 19; and
D-8 and 20 quiver; almost all others quiver slightly.
84
1830 About same as before, roderate vibration in central
region of far window rows PP, QQ, and RR, tubes 12
through 18. In near window shell periphery tubes
(defined at 1600) appear to buzz (at higher frequency)
when felt with finger.
2020 Most far window tubes moderately if not actively
vibrating.
2340 Far window tubes in rows RR, QQ, and PP, tubes 8 through
20 active, but probably not impacting. During an initial
exploratory run it appeared that the correspondingly
located central tubes in the near window started to
impact, but this could later not be substantiated with
instrumentation.
2400 The central region tubes in both windows are impacting.
Case 31
NTIW Bundle - 6 Crosspass - 600 Layout - 16% Baffle Cut
650 No significant observation.
850 Slight quiver of tubes G-5 and 7
1150 Same as 850.
1390 Quivering of tubes G-5 and 7, slight quivering of tubes
G-9, 19, 21, and 23, 00-9, 19, and 21. Tie bars in far
window, as seen through center port, vibrate about 0.8 mm
(0.032 in.) peak-to-peak.
1610 Same as 1390, except that tube 00-19 is quivering. Tube
00-21 is vibrating slightly and at higher flowrates will
be more active than any other tube. As the testing
progresses it becomes apparent that this behavior is
caused by .Zceraction with the (3-span, more flexibly
supported) tie bolt in location QQ-21. It is expected
that this behavior of tube 00-21 would not have occurredwith tie bolt QQ-21 absent, as would be the case in an
actual no-tubes-in-window bundle.
1890 Slightly increased activity, quivering are tubes G-5, 7,
9, 19, 21, and 23, 00-19 and 23. Slight quivering of
tubes 00-9, 13, and 17, and also of some non-saddled tube
such as NN-10 and 18, MM-17, and LL-10. Tie bars in far
window vibrate about 1.6 mm (0.063 in.) peak-to-peak.
85
2290 Same as before, quivering of tubes H-6, NN-10 and 22.
Slight vibration of tube 00-21 is continuing, tubesbetween it and tube MM-17 are slightly vibrating too.
Tie bars are vibrating about 2.5 mm (0.1 in.) peak-to-
peak QQ-7 and 21.
2690 About same as 2290, tubes NN-10 and 12 are vibratingslightly, too. Tie bolt QQ-21 is seen to "shudder"
occasionally.
2990 In far window most saddled and some of the tubes in the
adjacent rows are quivering or vibrating slightly. In
the near window there is not quite as much activity
noted. Tie bolt QQ-7 is shuddering to about 2.5 mm
(0.1 in.) peak to peak amplitude, but tie bolt QQ-21 is
not moving.
3370 Upon reaching this flowrate a loud vibration suddenlystarted. Tie bolt QQ-21 was observed to vibrate with
large amplitudes (at least 6 mm (0.25 in.) peak-to-peak)and QQ-7 was vibrating strongly too. These tie bolts,
unlike the tubes, are supported by only 2 baffles, wereapparently initiated into an instability. The adjacent
tube 00-21 was affected and was vibrating strongly; feltwith the finger it seemed to be a higher frequency. No
other tube was vibrating as much, vibration of some tubesin the saddled and adjacent rows was slight or at most
moderate.
Case 32
Full Bundle - 6 Crosspass - 600 Layout - 30% Transverse Baffle Cut
700 No significant observations
1050 Slight quivering of tube II-11, KK-3 and 25, and LL-24
1310 Quivering of tubes KK-3 and 25; slight quivering of tubes
C-19, D-20, J-4, K-25, II-11, 13, and 15, and LL-24.
1610 Quivering of tubes C-19, D-20, G-23, 1-23, 11-15 and 23,JJ-16, and (on the bundle periphery) KK-3, LL-4, 00-5 and
23, PP-6, SS-9, and TT-10. Slight quivering of tubes in
rows II (5 to 23) and JJ (6 to 20).
1750 As 1600, slight vibration of tubes C-19, D-20, RR-8,SS-9, and TT-10. More quivering in tube rows II through
MM, tubes 8 through 12.
86
1830 Slight to moderate vibration of central tubes in fa
window starts on rows II through MM, with tubes 11 to 17.
1950 More activity than at 1830, in far window shell periphery
region tubes above row 6 and below row 22 vibrate
moderately. In addition, most far window tubes in the
shell periphery regions above row 7 and below row 22
vibrate actively and may have impacted. The central
tubes of rows L and M in the near window are quivering.
2170 In the far window, the tubes next to the baffle edge in
the central region are impacting. The impact region is
roughly defined by tubes MM-14, JJ-16 and 20. Tubes in
the far window shell periphery regions are vibrating more
on the bottom (below row 20) than on the top (above
row 7).
2500 The region of impacting tubes also includes the far
window shell periphery tubes below row 22. By contrast,
the corresponding tubes on top, which at lower flowrates
had been the more active ones remain relatively calm. (A
subsequent instrumented test showed that the upper tubes
do not go unstable until 2910.)
Case 33
Full Bundle - 6 Crosspass - 600 Layout - 30% Parallel Baffle Cut
690 Tubes KK-25, MM-23, and 00-23 and 41 quiver very
slightly.
890 As 690, tube KK-26 quivers and KK-3 quivers slightly.
1170 Tubes KK-3, 23, and 25, LL-24, and MM-23 quiver; tubes
J-24, K-25, M-25, JJ-24, SS-19 and TT-18 quiver slightly.
1500 Tubes 1-23, J-24, K-25, M-25, 11-3, 5, and 25, JJ-24,KK-3, 23, and 25, LL-4 and 24, MM-5 and 23, and 00-5
quiver. Very slight quiver is noticeable in central
tubes of upper window rows L and M, tubes numbered 9 to
18, and also in lower window tube rows II and JJ unless
otherwise stated above.
1690 About same as before, but slightly more active. MM-23and 00-23 vibrate slightly.
87
1770 Tubes in rows II to 00 numbered 23 and 24 are vibrating
with shuddering (There may have been an instability
started already).
1950 Tubes D-36, JJ-24, and tubes 23 in rows II to 00 are
vibrating actively if not impacting, especially JJ-24 and
KK-23. Most remaining tubes in rows II and JJ next to
the baffle edge are vibrating slightly, so does tubeKK-3. Tube D-8 vibrates noticeably. It appears to the
eye that most of the vibration occurs in the central
span.
2210 Impacting of tubes 35 to 42 in rows II to 00. Also mostother tubes in rows II and JJ back to number 7 are
impacting. Active vibration observed of tubes LL-4,
MM-3, PP-5, QQ-6, and RR-5. No impacting observed in
upper window.
Case 34
NTIW Bundle - 6 Crosspass - 600 Layout - 30% Baffle Cut
1000 Tie bolt QQ-7 vibrates estimated 7 mm (0.03 in.) peak-to-
peak. Apparently is excited by tie bar. None vibrate onbottom. No significant tube vibration.
1200 Tie bolt QQ-7 vibrates 1.5 mm (0.06 in.) peak-to-peak.
Otherwise same.
1600 As 1200.
2000 As 1200, except QQ-7 2.3 mm (0.09 in.) estimated. Noiseheard in shell on opposite-to-nozzle side, near outlet
end. Still no significant tube vibration.
2400 Tie bolt/bar vibration quickens to higher frequency, nowon bottom too. Estimates are QQ-7 2.3 mm (0.09 in.) and
QQ-21 0.06 in. peak-to-peak. Still no significant tube
vibration.
2780 About same as 2400. Tubes still quiet. Slight quivering
of tubes P and FF-26.
3220 Substantial high frequency vibration in central part of
bundle, particularly row 12, T-12 moved towards outerend. Probably is -70 Hz natural frequency. Appears to
be some type of instability.
88
Scans Performed at least 6 scans to investigate initiation of
buzzing type of instability. At 2880, 4 to 5 central
tubes in rows 12 to 15 start buzzing. At 3200, region of
buzzing expanded 5 to 6 central tubes in rows 10 through
16. Ceases at 2700. No major vibration of other,
particularly saddled tubes.
Case 35
7-Crosspass - 30 Layout - Transverse Baffle Cut
800 No significant vibration
1000 Slight high freqeuncy buzz felt in tubes A-23 through 27,
and tubes B-24 through 28.
1200 Buzz in tubes A-23 through 27, slight buzz in tubes B-18
through 30, C-15 through 25, and D-14 through 24, andF-28.
1400 As 1200, buzz also in all tube B rows, slight quiver of
tube W-41.
1600 Buzz in row A is somewhat reduced, but buzz extends torow D. Quiver of tubes W-9 through Z-13 and V-42 and
W-41.
2000 Quiver in shell periphery tubes U-5 through Y-11 and U-43through Y-37, slight vibration of "exposed" tubes Y-11
and 37; slight quiver of tubes V-17 through 29.
2200 As 2000, stronger buzz of row A tubes, slight vibrationof tubes B-32 and C-33 through 37. Quiver of shell
periphery tubes D-38 through F-42. Slight quiver of
tubes U-17 through 29.
2400 As 2200, buzz extends to central part of row D. TubeB-28 "flops" up and down occasionally. Tubes U-5 to 11
and 37 to 41 are quivering. Tubes W-7 and 41 vibrate
moderately.
2580 Considerable high frequency buzz in rows A, B, and C,strongly buzzing are tubes B-16, 18, 30, and 32 and C-31
through 37.
2720 On first approach to this level, instability initiatedfirst in near window at this level, but during all
subsequent tests threshold occurred at or above 2900.
89
Case 36
7-Crosspass - 30 Layout - Parallel Baffle Cut
740 No significant vibration.
1000 Slight quiver of "corner" tube U-5.
1300 Slight quiver of shell periphery tubes U-5 through Y-11.
1600 Slight quiver tubes U-5 through 9, also AA-29, Z-32, andY-35. Quiver of tubes V-6 and 8, W-7 and 9, and X-10.
Very slight quiver of corner tubes G-5 and 7.
1780 Same as 1600, peripheral tubes G-5 through C-11 and C-37through G-43 quiver lightly.
2000 Tubes U-5 through 11, V-6, W-7, and Y-11 vibrate
actively, tubes G-5 and F-6 quiver.
2200 Tubes in "corner" triangle U-5 Through 11, V-6 through
10, and W-7 are very active.
2350 Tubes U-5 through 11, V-6 through 10, and W-7 and 9 areprobably impacting. Quivering seen along shell periphery
tubes Z-16 through 32 and Y-37 through U-43; also tubes
G-5 through C-11. Active vibration - if not impacting -in corner region defined by tubes U-5, U-17 to Y-13.Moderate vibration of shell periphery tubes Z-36 through
W-4 3.
2400 Tubes within region defined by tubes U-5, U-17, Y-13, and
shell periphery are impacting.
2460 Active vibration - if not impacting - in region definedby tubes U-5, U-19, Z-14, and shell periphery. Moderate
vibration of shell periphery tubes Z-36 through W-43.
2630 Large increase in noise level.
Case 37
7-Crosspass - 90* Layout - Transverse Baffle Cut
1000 No significant observations.
Slight quivering of tubes R-3, S-3, W-9, 10, and 11.1200
90
1400 Moderate vibration of tube W-9, quivering of tubes R-21,S-20 and 21, V-8 and 9, and W-10 and 11. Slight
quivering of tubes S-3, T-4, and neighbors. In nearwindow, there is slight high frequency quivering in rows
A through D, most noticeable in tubes B-b and 16, C-7, 8,and 16.
1600 Same as 1400. Quivering of groups of tubes at or near
shell periphery such as R-3 through V-5, R-21 through
V-19, A-14 through F-21.
1820 About same as 1600. Group of tubes quivering extends
towards centr of bundle, roughly rows A to F between rows
8 through 19.
2000 Moderate vibration at or near shell periphery tubes in
far window, particularly tubes R-3, 20, and 21, S-3, 4,
20, and 21, T-4 and 20; but there is only a quiver in
central tubs of next-to-the-baffle edge row R. Slight
high frequency buzz felt on almost all near window tubes.
2120 More activity than 2000.
2210 Central tubes in row R indicate slight "shuddering," feel
'"jumpy.
2270 Initiation of impacting in far window rows R, S, and T
tubes 6 through 17. Also substantial vibration in lower,
far window shell periphery tubes, particularly R-21, and
S-20 and 21.
2670 Initiation of instabili-:y on near window, group of tubesapproximately defined.
Case 38
7-Crosspass - 900 Layout - Parallel Baffle Cut
900 No significant observation, slight quivering of tubes R-3and 7.
1200 Quivering of tubes near the inlet nozzle in first flow-
turn-around window (i.e., not supported by first baffle
from inlet), these tubes are Q-2, R-3 and 4, S-3 and 4,
T-4, and U-5.
As 1200, slight quiver of tube E-3.1400
91
1600 Quivering of tubes R-3 to 5, S-3 to 5, T-4 and 5, and
U-5; slight quivering of tubes in rows R through U tubes6 through 8. Very slight quivering of tubes in row W and
in rows C through G tubes up to number 7.
1800 Same, but a bit stronger than 1600, feel quiver with handin most of first window tubes up to row 16, including
saddled tubes Q-2 through 5. In the other "corner"
regions, quivering of tubes E-3, D-4, and E-5, also
slight quivering of tubes in rows C through F up to row
5, D-20, and tubes R-20 and 21, S-20 and 21, and T-20.
1950 Tubes R-3, S-3 and 4, and T-4 vibrate vigorously, appearto be impacting.
2220 Tubes R-3, S-3, and T-4 are impacting, apparently in thebaffle holes. Subsequent evaluation of instrumentation
records could not positively identify the occurrence oftube-to-tube collision, even though tube S-3 hit
sufficiently strong to be forced into rotation.Similarly tubes R-9 through 14 are vibrating actively.
2400 Tubes in central area of first window are impacting,i.e., tubes R-7 through 17, S-8 through 16, and T-10
through 13. Tube S-3 is also impacting, with neighboring
tubes vibrating vigorously too. Tubes in rows R, S, and
T numbers 19 through 21 vibrate actively.
Case 39
Double-Segmental, 3 Core/2 Wing Baffles - 300 Layout - Parallel Baffle Cut
970 No significant observations.
1170 Slight vibration of tubes F-6 and 8, E-7, and V-6. Tubes
B-18, 20, and 22 are quivering.
1420 Same as 1170. Tubes W-7 and 9 are quivering, tubes X-10,
12, and 14 are quivering slightly.
1600 Tubes E-7 and V-6 vibrate actively, tubes F-6 and 8, E-9,
D-10, B-14 and 16, V-8, W-7 and 9 are vibrating
moderately. Tubes A-19, 21, and 23, and tube U-7 are
quivering.
2040 Regions of moderately and slightly vibrating tube expandsin "corner" regions V-6 to V-12 to X-10 and F-6 to F-12
92
to B-14. Tubes AA-19, 21, and 23 and E-41 arequivering. Tube V-6 observed to flip-flop occasionallyfrom one side to the other in the flow direction.
2200 Tubes in "corner" regions listed at 2040 are vibrating
stronger, tubes F-6, 8, and 10, and V-6 are very active,
F-6 is impacting somewhere, probably the baffles. Tubes
in first 2-3 rows (i.e., numbered 1 to 6) facing nozzle
in core region (rows J through R) are quivering slightly.
2350 Tubes V-6, 8, and 10 vibrate actively. All tubes in rows
A and AA are quivering. Otherwise as 2200, except thathigh frequency buzzing is noticeable in core region tubes
referenced above, particularly in the bottom rows L, K,
and J.
2440 "Corner" regions in top and bottom window become veryactive, tubes F-6 and E-7 are impacting (not necessarily
tube-to-tube).
2840 Lowest flowrate at which tubes in central region in the
rows next to the core baffle edge in the top outer window
went into instability. Tubes involved are V-16 through
32, W-17 through 33, X-18 through 34. Other tubes
defined by region V-34, V-40, Y-37, Z-34, and Z-30 are
very active. There is also strong vibration in the"corner" regions described previously. Tubes in the core
region adjacent to the nozzle indicate high frequencybuzzing vibration, particularly in rows J through M,
numbers 3 to 7. Buzzing vibration of tubes in second
position is more pronounced than of the tubes directly
exposed to the incoming flows.
2990 Almost all tubes of rows V, W, X, and Y are unstable.
3280 Instability initiates in the tube rows next to the corebaffle edge in the bottom outer window.
Case 40
Double Segmental, 3 Core/2 Wing Baffles - 30 Layout - TransverseBaffle Cut
1000 No significant vibrations.
Tubes B-14 and 16 quiver slightly.1200
93
1300 Tubes C-11 and 13, D-10, E-9 and 11 quiver; tube A-29quivers slightly.
1500 Tubes C-11 and D-10 quiver more strongly.
1600 Tubes along the periphery from C-11 through F-6, and alsoF-8, and from C-37 through E-41 are quivering.
1850 Tubes in region defined by B-16, F-12, F-6, and theperiphery quiver if not vibrate slightly. Also quivering
are tubes B-18, C-17, and D-16, and along the bottom
periphery between tubes B-32 through F-42, also F-40.
1910 Some sort of instability starts in top peripheral region,as well as in central region rows A through C, tube
numbers 11 through 28. Some tubes are impacting, in the
central region, particularly C-17 and B-28 are very
active.
2010 Impacting observed along top shell periphery involving
tubes C-13 through F-6, also D-12 and F-8. Impacting
also observed in central region rows A through D tube
numbers 20 through 28 approximately. Tubes along bottom
periphery are vibrating moderately, but not as active.
No vibration beyond quivering observed in core region,
i.e., in row J and beyond.
2760 Most tubes in region between D-10 and F-40 and 2 to 3
rows deep from inlet nozzle are impacting. Instability
initiates in central regions of rows adjacent to baffle
cut, tubes E-19 through 29 and F-14 through 32 areinvolved.
Case 41
Double Segmental, 3 Wing/2 Core Baffles - 300 Layout - Transverse
Baffle Cut
700 No significant vibration.
970 Tubes A-21, C-11, and E-/ quiver slightly.
1220 Tubes in row A quiver slightly.
1390 Tubes in row A quiver at high frequency. Slight quiver
in row B tubes felt with finger but not seen. Tube C-37
quivers slightly.
94
1620 Tubes in rows A and B and in rows C and D above C-23 andD-22 quiver. Slight quiver felt in remaining tubes of
row C.
1870 Buzz-like quiver in tube rows A, B, C, and D and in rows
E and F in top and bottom tubes near shell periphery.
2100 As 1870, light buzzing noticeable in rows A, B, and C,
but amplitudes are still small.
2340 Moderate buzzing in rows A, B, and C. Tube C-17 moves
axially. Central window tubes J-2 and 46, and R-2, 24,
and 46 are quivering.
2640 Instability initiates in central part of tube row J,effecting tubes J-14 through 30 and K-19 through 23.
Tubes L-16, 18, and 20 are active, bottom tubes J-46,K-44, and R-46 vibrate moderately. Row A tubes vibrate
actively.
2810 Region of impacting extends to tubes K-15 through 29, and
L-20 and 21.
3100 Instability initiates in central tubes of row R.
Case 42
Double Segmental - 3 Wing/2 Core Baffles - 300 Layout - Parallel Baffle Cut
1000 No significant vibration.
1200 Tubes L-2 and 4, M-3, N-2 and 4, 0-3, and P-2 located
directly under nozzle quiver slightly.
1390 Slight quiver of central window tube rows J through R,
numbered 1 through 5 and 6 (biased towards top of
window). Soem rattling (baffle hitting) seen on
accelerometer traces, particulary on tube R-4. Very
slight quiver of "corner" tubes F-6 and V-6 in outer
window.
1640 Central window tubes numbered 1 through 8 quiver and up
to umber 13 quiver slightly. Additional tubes in bottom
outer window E-7 and F-8 quiver slightly.
1820 Increased activity, central window tubes (rows J through
R) numbered 1 through 9 are quivering if not vibratingslightly.
95
1980 Similar to 1820, with slight shuddering on central window
tubes numbered 1 through 9.
2250 Increased activity, slight to moderate vibration of
central window tubes numbered 1 through 8 and of wingwindow "corner" tubes E-7, F-6 and 8.
2350 Active vibration of central window tubes numbered I
through 7, biased towards top of window.
2500 Severe vibration if not impacting of central window tubes
forward of line connecting K-3 to R-8, approximately.
2600 Wild and loud impacting in forward central window tubes.
Case 43
Double Segmental - 3 Core/2 Wing Baffles - 450 Layout - Parallel Baffle Cut
1000 Tubes U-3, Z-6, and AA-5 quiver slightly.
1200 Tubes H-4, U-3, Z-2 and 4, and AA-5 quiver. Additional
tubes in first or second row from nozzle in rows H, M, 0,
P, Q, R, S, Z, AA, BB, and CC quiver slightly.
1390 Tubes in central window rows M through U up to tubenumber 4 or 5 buzz slightly. Tubes Z-6, AA-5, and BB-5
vibrate slightly. Tubes Z-8 through 20 and E-7 to H-4
quiver. Tubes H-6 through 22 quiver slightly, so do
C-25, D-26, and Z-22.
1640 Tubes in central regions rows L through V number 6 or 7
buzz slightly. Tubes in outer windows between nozzle and
line A-15 to D-16 to H-14 on bottom and Z-18 to FF-12
quiver; so do tubes C-25 through G-29.
1840 Tubes in central region up to row 8 are buzzing. Cornertubes up to row 6 in top and row 12 in bottom window
vibrate slightly. All other tubes in the first and
second rows from the core baffle edge, i.e. in rows G, H,
Z, and AA, quiver slightly.
2060 Somewhat increased activity compared to 1840. Tubes inlines C-25 to H-30 and B-22 to H-28 quiver.
2200 Ten tubes closest to the nozzle in the top outer window
"corner" appear "jumpy" with shuddering bursts. More
96
than half of tubes in lower outer window vibrate slightlyto moderately; there is little activity between rows 17
and 23.
2550 Four-span tubes in central rgion up to row 9 buzz
strongly, severe buzz in front tubes facing the nozzle.
Tubes in top outer window region up to tube line DD-8
through Z-12 are vibrating moderately. In the bottom
window, tubes outward of the ube line B-22 to H-28 are
quite active, and may be colliding with each other.
2740 In bottom outer window many tubes are very active and
some may be impacting: these are mainly in the central
region from rows H to C and along the shell periphery
between rows B and H.
2850 Four span tubes in central window up to row 8 buzzstrongly. Most tubes in bottom outer window are very
active, but this is not so on top outer window wherethere is some moderate, mostly relatively little
vibration activity.
3000 More severe activity in bottom outer window particularly
along shell periphery on inlet side.
Case 44
Double Segmental - 3 Core/2 Wing Baffles - 450 Layout - Parallel
Baffle Cut - 14 inch Size Nozzles.
800 No significant vibration.
990 Three-span tubes in "corner" locations H-4 and Z-4 quiverslightly. The "corner" locations occur in the top and
bottom outer windows next to the inlet/outlet nozzles in
the corner formed between the edge of the core baffles
and the shell periphery where the flow has to negotiate a
complex turn around the core baffles next to the end
zones.
1200 Tube H-4 is quivering, additional corner region tubesnear shell periphery quiver slightly: G-5, F-6, E-7, Z-4,
and AA-5; also tube C-25.
1390 About same as 1200.
1620 Tubes in corner regions quiver: H-4 through E-7, AA-5,Z-4 and 6; also H-26. Slightly quivering are shell
97
periphery tubes D-8, C-9, B-12, C-25 through E-28, BB-6
through EE-9, and AA-29. A very slight high frequency
buzz is felt on the ends of the four-span tubes in the
central window in rows 1 through 4 next to the nozzles.
1820 Tubes in outer window "corner" regions forward of (.ndincluding) Z-8 through BB-6 are vibrating slightly, so
are tubes forward of C-9 through G-9 and Z-12 through
DD-8, and outward from F-28 through H-26. The tubes of
rows 1 through 5 in the central window buzz slightly,
tube V-2 strongly.
2020 Tubes in outer windows vibrating slightly to moderately
are in lines C-9 through H-4 and D-10 through H-6 as well
as Z-4, Z-6, and AA-5. Tubes in rows H and Z, 14 through20 next to baffle edges also vibrate slightly, regions ofquivering extended slightly. Region of slight to
moderate buzz in central window extends from rows 1 to 8
approximately.
2390 Slight to moderate vibration in bottom outer window in
row H and inward of row 11. Slight vibration of tubes
B-22 through H-28 and C-25 through H-30. Moderate
vibration in top window "corner" region inward of tubes
Z-10 through C-7.
2470 Somewhat stronger and extended region of activity than2390. Tubes buzzing in central window extend from rows 1
through 10. Vibration of some tubes creates a fine spray
of water.
2760 Almost all tubes in bottom outer window vibrate. Tubes
near baffle edge in central part of row H vibrate
strongly, certain to impact baffles even though no tube
to tube collisions can be ascertained. Tubes in lower
central region and along bottom shell periphery on inlet
side are vibrating actively, particularly tube rows B-12
through E-9. Tubes Z-6 and AA-5 in top outer window
vibrate actively, another dozen tubes in corner vibrate
moderately. Tubes in central window buzz strongly up to
row 8. ,
3050 Almost all of bottom outer window tubes vibrate actively,apparently impacting the baffles, some so strong that
they may be impacting tube-to-tube. (Some of these,
i.e., C-11, D-10, and E-9, were subsequently instru-mented, but tube-to-tube collisions could not be
verified.)
98
Scans In genral, the tube amplitudes rose gradually with
flowrate. In the bottom outer window appeared to be a
small noticeable increase of activity in the 2500 to 2700
range, even though tube-to-tube impacting could not be
verified.
3510 Up to this flowrate, relatively little activity was
observed in the top outer window, with the exception ofmoderate vibration in the corner region at higher
flowrates. At this flowrate there was observed anoticeable increase of vibration in the corner region and
along the baffle edge (row H) bct again no tube-to-tube
collisions could be verified.
Case 45
Double Segmental - 3 Core/2 Wing Baffles - 45* Layout - TransverseBaffle Cut
700 No significant observations.
1020 Tubes C-17, B-16 and 18 quiver slightly.
1240 Tubes within and in front of "triangle" B-14, E-17, B-20quiver, so do a few adjacent tubes. Many tubes in near
outer window quiver slightly, particularly those along
the top and bottom shell periphery, also tubes H-8 and
26, and pubes within and in front of lines C-11 to H-16
and H-18 to C-23.
1400 About same as 1250; most tubes in near outer window
quiver slightly, including saddled tubes K-7 and 9.
1610 Some tubes in near outer window vibrate slightly: mostnoticeably A-8, 10, 12, 14, 26, and 28, E-7 and 27, D-8
and 26, C-11 and 23 and B-20. Slight high frequency buzzfelt on frontal tubes in rows A to D. Baffle edge tubes
L-12 through 20 quiver slightly.
1850 Almost all tubes in near outer window are vibratingslightly, with buzz felt in frontal region as for 1610.
There is also slight quiver of tubes T-18, U-17 and 19,
and '-18 in central window and tubes of rows Z to EE
along top and bottom shell periphery in far outer window.
2120 About same as for 1850, most keenly felt slightvibrations in front of row D, along shell periphery, and
99
along baffle edge in rows G and H in near outer window.
In central window tubes in row L and in the center of
rows T, U, and V are quivering.
2380 In near outer window slight to moderate vibration if
tubes in rows A through D, and along bottom shell
periphery. Almost all tubes in window vibrate slightly,
including all of row H. Specifically active tubes were
G-15 and 17, and H-26 and 28. In central window there is
slight quivering or quivering in the central portions
(numbers 8 to 28) of rows L, M, N, U, and V. In far
outer window tubes in rows Z and AA, numbers 12 to 22
quiver slightly.
2540 In near outer window the frontal tubes in rows A throughD vibrate moderately to actively. Specific active tubes
were D-8, E-25 and 27 (instrumented), and F-26. Quiver
felt with hands along both baffle edges and in central
region (rows N through S, number 5 through 31) of central
window. Quivering felt in central region of the far
outer window also.
2770 Tubes in frontal region rows A through D in near outerwindow appear to be unstable (Note: tube-to-tube
collision could not be proven at this flowrate from
available instrumentation).
2970 Frontal area appears "wild."
3100 Tube-to-tube impacting in near outer window becomesloudly audible.
Case 46
Double Segmental - 3 Wing/2 Core Baffles - 450 Layout - Transverse
Baffle Cut
790 No significant observations.
900 Tube L-3 is slightly quivering.
1000 Tubes in rows A, B, and C-13, 19, and 21 are quivering
slightly.
1200 Slight quiver felt, but not seen, in ncar outer window of
tubes C-25 through H-30 on bottom facing shell periphery.
100
1290 Slightly quivering buzz felt, but not much seen, in frontrows up to row D. Tubes in row L from number 10 downward
quiver slightly.
1500 Tubes in rows A and B are buzzing. Tubes in rows C, D,and L (from number 8 down) as well as H-12, 14, and 16
and G-17 are quivering. Many tubes in rows G, H, and in
the central portions of rows M and N are quivering
slightly.
1710 Tubes in rows A and B under nozzle buzz strongly. Shellperiphery tubes of rows C through H quiver, as do the
tubes in the central portions of rows H, M, and N.Slight quivering occurs in the top and bottom tubes of
the central window (rows L through V) and in tubes V-10
to 22.
1910 About same as 1720. Tube A-15 in front rotates as a
consequence of strong buzzing. Tubes C-9 and 25 and D-8
and 26 quiver.
2000 Buzzing of front tubes appears somewhat reduced. Bottomtubes of central window quiver with L-32 vibratingslightly. Central tubes of rows Z and AA quiver
slightly.
2180 About same as 2000. Moderate buzz from row D towardsfront.
2400 Inzreased buzzing, rows A through C strong, D and Emoderate, row F slight. Tubes in central portion of rows
G and H and on bottom of rows L, 0, P, and S vibrate
slightly.
2720 About same as 2400
2850 Noise level of tube bundle increases.
2940 Tube bundle is noisy. Strong buzz in front tubes up torow D.
3300 Bottom tubes in central window vibrate moderately.
3380 Central tubes in rows L, M, and N vibrate moderately,tubes in row L appear "jumpy."
3550 Lowest flowrate at which initiation of instability in rowL is observed with strong tube impacting (against baffle
101
plates) occurring, but tube-to-tube collisions are not
verifiable. Instability also observed in row M and insaddled row K.
4040 Tube-to-tube impacting likely.
3270 When flow is reduced to this level, large vibrations
appear to diminish.
Case 47
Double Segmental, 3 Wing/2 Core Baffles - 450 Layout - Parallel Baffle Cut
700 No significant vibration.
920 Slight quiver felt, if not seen, in central seven
row/aard 2 tubes, also L-6, M-3 and 5, U-3, Q-3 and U-5.
1120 Additional slightly quivering tubes are F-5, G-4 and 6,
and Z-4.
1310 As before. Quiver seen or buzz felt in almost allfrontal ceLtral window tubes in rows L through V numbers
1 through 4. Central region tubes in rows N through U
numbered 1 and 6 are quivering slightly.
1470 Central window tubes M-5 and 7, N-4 and 6, 0 through R
numbers 1 through 5, and S-1 and 3 are buzzing slightly.
Tubes next to the baffle edges in rows L and V numbers 6through 12 are quivering.
1620 About same at 1470. Tubes in an in front of N-2 to Q-5to T-2 "triangle" are buzzing.
1870 Stronger buzzing in front. entral window up to tubesnumber are quivering. Tubes near edge in rows L, M, U,
and V up to number 25 are quivering or slightly
quivering.
2070 Same as 1870. Tubes L-4 and 6 and V-4 and 6 appear"jittery," almost unstable-like.
2220 Moderate vibration of central window tubes up to row 3.
2350 Tubes V-2, 4, and 6 appear to be unstable. (However,
tube-to-tube collisions could not be verified from theacceleration signals of instrumented tube V-2.)
102
2420 Strong instability type vibration (but possibly without
tube-to-tube collisions) of central window tubes up to
and including row 4, also L-6 and 8, M-5, U-5 and 7, and
V-6. Frontal tubes M-3, N-2, and 0-1 move out axiallyfrom the strong buzz.
2540 As 2430, most central tubes in and in front of wedge L-8to Q-3 to V-8 appear to be unstable. Tubes all along
rows L and V quiver at least slightly.
2650 About same as 2540, except more active. (Instrumentedtube Q-1 indicates possible tube-to-tube collision.)
2810 Vibrations large in front, central rows. Instabilitytype action in rows L, M, N, T, U, and V up to tube
number 15, in rows 0 through S up to tubes number 9. No
significant observations recorded in outer windows.
Case 48
Simulated U-Tube Test - 4 Crosspass - 300 Layout
800 No significant observations.
1000 Slight buzzing, not seen but only felt with fingers of
tubes A-21 through 29, and B-24.
1300 As 1000, buzzing also felt in tubes B-22 through 30.
1650 Shell periphery tubes E-7 and Z-11 are quivering, tubesU-3, V-4, and W-5 are quivering slightly.
1710 Region of buzz in front of nozzle expands in rows A and Bto tubes numbered 15 trough 30. Adjacent tubes in rows C
and D buzz slightly. Tube E-19 quivers, so do shell
periphery tubes U-3 through V-Il including V-8. Tubes
U-43 and V-42 quiver slightly.
1970 As 1710 with slight vibration of shell periphery tubesW-41, X-10, Y-11 and 37. Tubes E-7 and 41, U-43 and V-42
are quivering.
2100 As 1970, tubes U-19 through 29 quiver slightly. Morequivering of shell periphery tubes in rows U through Y,
on top and on bottom.
2210 Moderate buzz in front rows, especially tubes A-23through 29 and F-42.
103
2610 About same as 2210, central row U tubes are a little
"jumpy."
2900 Strong buzz in row B.
3050 Central row U vibrates in s;'urts.
3150 Tubes in rows U, V, and W in central region (tubes
numbered 13 through 34) appear to be unstable. Strong
buzzing of central tubes in rows A through D.
104
Distribution for ANL-85-66
Internal:
DruckerS. ZenoW. Wambsganss (90)E. HoltzW. SchertzS. ChenH. ChungHalle (90)
J. A. JendrzejczykT. M. MulcahyS. K. ZussmanANL Patent Dept.ANL Contract FileANL LibrariesTIS Files (5)
External
DOE-TIC, for distribution per UC-95f (239)Manager, Chicago Operations Office, DOEDirector, Technology Management Div., DOE-CHD. L. Bray, DOE-CHD. Goldman, DOE-CHComponents Technology Division Review Committee:
P. Alexander, Flopetrol Johnston Schlumberger, HoustonD. J. Anthony, General Electric Co., San JoseA. Bishop, U. PittsburghB. A. Boley, Northwestern U.R. N. Christensen, Ohio State U.R. Cohen, Purdue U.R. E. Scholl, URS, San FranciscoJ. Weisman, U. Cincinnati
H.R.M.R.W.S.H.H.
