GAT)(GENERAL AMERICAN TRANUPORTATION CORPORATION

FRICTION LOSS IN FLEXIBLE

S-ý PLASTIC AIR DUCT

by

R. B. NeverilH. F. Belils

Q9 OCD Work Unit ]1423A

GARD Report 1278-2 October 1965

Distribution of' this document is unlimited.

IL AND

GENERAL AMERICAN RESEARCH DIVISION

7443 NORTH NATCHEZ AVENUE. NILES. ILLINOIS 50648 312/847.400oO

Prepared forOffice of Civil Defense

Department of the Army, OSAunder

Work Unit 1423ASRI Subcontract No. B-70925(4949A-28)-US

FRICTION LOSS IN FLEXIBLE

PLASTIC AIR DUCT

by

F. B. NeverilH. F. Behls

0CD Work Unit 1423A

GARD Report 1278-2 October 1965

Distrioution of this document is unlimited.

Reviewed by: Approved by:

G. Engholm P7 Ro63nbergGroup Leader General ManagerEnvironmental Research

REVIEW NOTICE

This report has been reviewed in the Office of Civil Defense and a:•roved forpubli:ation. Approval does not tignify that the contenta necesaaril]y reflectthe views and policies ofi the Ot'tll"e of Civil Defenst.

FOREWORD

The General American Research Division (GARD) of General American Trans-

portation Coi-poration (GATX) was contracted by Stanford Research Institute

(SRI) for the Office of Civil Defense to design, fabricate, and test flexible

plastic tubing and fittings which would provide a system for handling venti-

lation air in fallout shelters when used with the shelte-r ventilator (shown

below) specified in MIL-v-40645., "Package Ventilation Kit, 20-Inch Fan, Modular

Drive (Civil Defense)". This program was performed under SRI Subcontract

B-70925(4949A-28).-US with Mr. C. A. Grubb serving as project monitor.

PACKAGE VENTILATION KIT IN OPERATION

0NWM AL AMittAN MONBA3M @VItStN

Il

'I

ABSTRACT

I I Tests were conducted to determine the pressure drop characteristics of

20-inch diameter, 4-mil thick, polyethylene tubing and both factory and.

shelter fabricated 90-degree elbows. The tests were performed at flow rates

Sranging from 1300 to' 4100 cubic feet per minute. These plastic components

are part of a portable ventilation system that has been developed for Civil

Defense fallout shelters, Specification MIL-V-40645.

5 Fully inflated 20-inch diameter plastic tubing has about t~hree-quarters

of the pressure drop of sheet-metal duct. However, the last fifty feet of a

I plastic duct system, which is not completely inflated, has 1-1/2 to 3 times theSduc

pressure drop per foot of fully inflated plastic tubing. The result is that

Sfor duct systems over 100 feet long th, pressure drops for sheet-metal and

plastic tubing are approximately the same.

'Me friction losses for both factory fabricated and shelter fabricated

elbows were established. A 40-inch, smooth radius, 90-degree factorya fabricated elbow is recommended for use with the Civil Defense Package

Ventilation Kit. This elbow develops a pressure drop equivalent to 50 feet

of straight tubing. The best shelter fabricated elbow is a three-piece elbow

with a radius of 60 inches that can be fabricated from the straight tubing

[ and tape stocked in the Package Ventilation Kit. This elbow develops a

pressure drop equivalent to 90 feet of straight tubing.

I

UNNIMAL AMERICAN REUHARMH OIVISION

' iii

TABLE OF CONTENTS

-SECTION Pag-

FOREWORD .. . . . . . . . . . . . ... . . . . . . .i.. . ii

ABSTRACT-. .... ....... ............. iii

1 INTRODUCTION.. ..... .... . 2

2 TEST PROUCFI)ES. . ....... . . . . ............. 3

2.1 Apparatus .............. ......................... 3

2.2 Methods ..................... ....................... 3

2.2.1 Tubing ........................................... 8

2.2.1.1 Duct Adaptor............................... 8

2.2.1.2 PVK Application........................... Q

2.2.2 Elbows .................. .... ............... 11

2.2.2.1 Factory Fabricated Elbows ................. 11

2.2.2,2 Shelter Fabricated Elbows............. 12

3 RFSULTS AND ANALYSIS .......................................... 19

3.1 Tubinrg...............................o. ......... 19

3.1.1 Duct Adaptor ................................ 23

3.1.2 Condition of Duct ........................ 23

3.2 Elbows. . . . .......... o ........................ o ........ o .o.. 25

3.2.1 Factory Fabricated Elbows ......... ...... 27

3.• 2 Shelter Fabricated Elbows ................... 9

4 SMM4ARY AND RECOMMENDATIONS.. . o.......... o .... o ............ 33

REFERENCES ........... oa.................... ........... 38

APPENDIX A - Test Data ........................ . ......... 39

APPENDIX B - Specification Used for Determining Cost ofFittings ........... ....... o................. o..... 49

GIENERAý, AMBRICAN REQEARC14 0IVIBIONiv

LIST OF FIGURES

I FIGURE NO.

1 Package Ventilation Kit (PVK) I2 PVK Duct Systems 23 Test Apparatus 54 Schematic Layout of Test Apparatus 6

I5 Friction of Air in Straight Spiral Conduit Duct 76 Test of the Tubing with the End Unrestrained (Free

Air Discharge)7 Test of the Tubing with the Duct Adaptor 98 PVK-Duct Test 10

9 Wire-reinforced Elbow 1310 Hand-tucked Elbow 1311 Shelter Fabrication of a 60-inch Radius, 90-degree,

Three-piece Elbow 1512 Shelter Fabricated Three-piece Elbow in Operation 1613 Shelter Construction of the Packing Box Elbow 1714 Packing Box Elbow in Operation 1815 Friction of Air in Straight Polyethylene Tubing 2116 Wrinkles in New Tubing 2417 Pressure Drop, Comparison of 90-degree Elbows 26.18 Instability in Miter Elbow 2819 Friction Loss of the 40-inch Smooth Radius Elbow 3020 S;helter Fabricated Elbows in Operation 3121 Friction Loss of the Three-piece, 60-inch Radius,

Elbow 3222 Factory Fabricated Elbow (Modified) 3523 Test Data -- 50 Feet of Tubing 4o24 Test Data 100 Feet of Tubing 4125 Test Data -- 150 Feet of Tubing 42S26 Test Data -- 200 Feet cf Tubing 4327 Test Data -- 250 Feet of Tubing 4428 Test Data -- 300 Feet of Tubing 4529 Test Data - 350 Feet of Tubing 46

30 Test Data -- 400 Feet of Tubing 4731 Test Data -- 450 Feet of Tubing 48

[EI:

GFOUVRAL AMCRICAN W9IUAPCH 01VISeON

v

Fan Package

Drive~ Wdule Psc.kvje

Fliure I PACKAGE MMIATJ(ON KIT (PVK)

I

SECTION 1

I INTRODUCTION

A Package Ventilation Kit (PVK) was developed (see Figure I and Ref. :)

for use as an inexpensive method of exhausting iftale, hot and humid air from

fallout shelters. This ventilator is intended for use with flexible plastic

duct systems (see Figure 2).and, therefore, flexible plastic tubing and fittings

are supplied with the Kit. The objectives of this program are to determine the

I tfriction loss of flexible tubing and fittings, and to recommend the best

fittings, based on cý.st and pressure drop, for use in fabricating shelter duct

systems.

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,I

SECTION 2

TEST PROCEDURES

2.1 Apparatus

The test apparatus consisted of an 80CO cfm centrifugal blower connected

by a flexible wire-reinforced cloth duct to a 47 foot long, 20-inch diameter

test stan. which was fabricated from "L U.S. Gage, zinc coated steel spiral

conduit duct with 6 inch seams (see Figures 3 and 4). The design of the test

stand is based on recommendations of the National Electrical Manufacturers

Association (Ref. 2). Air flow rates were measured with a lU-inch diameter

aperture sharp-edge orifice plate which was calibrated with a pitot tube five

feet upstream from the orifice. Two air straighteners were located approxim_.t: ly

14 feet and 28 feet upstream of the orifice plate to reduce turbulence. A

piezometer ring was located 14 feet downstream from the orifice and 5 feet from

the end of the test stand. Inclined manometers were used to measure the pre.-

sure drop across the orifice, and the static pressure drop of the test speci-!ne-s.

2.2 Methods

The specimens were first taped to the test stand. The blower was adjusi• i

to provide the desired flow rates, and the static pressure loss and flow rate

(orifice differential pressure) were recorded. Barometric pressure, dry-bulb

temperature, and wet-bulb temperature were recorded before each test to providt

the flow rate correction factor to standard air . = 0.075 lbs/cu ft). The

tare pressure drop of the test apparatusi.e., the pressure drop caused by th7

5 foot length of spiral. duct between the plane of the measuring station and

the plastic specimens,was suotracted frcm the test data after its correction t'*

GENERAL AMERICAN RESEARCH DIVISION

m

standard air. To establish the tare pressure drop, the friction loss for 100

1 feet of 20-inch spiral duct -- as measured from the static pressure measuring

J station -- was determined with the apparatus described above, and the results

are shown in Figure 5. The tare pressure drop for the leugth of spiral conduit

between the static pressure measuring station and the test apecimen was

calculated by multiplying the values of Figure 5 by 0.05 (see Table I); i.e.,

I Tithe ratio of the five foot length to the total 100 feet spiral duct tested.

lTable I

Tare Pressure Drop of the Test Apparatus

Air Flew Tare Pressure Drop(cfm)- (inches of water Lagej

1200 0.001014oo 0.00131600 ,o oo181800 0.00222000 . 002d2200 0.0033i4 2400 Q.0039260o0.0•

2800 0.00523000 0.0059I I3200 0.006634oo 0.00753•0 0.00633600 0.409.14W000 .000I I •4200• 0.0110

As shown in Figure 5 the friction ,r air Ir straight &piral duct, as

m.nutactured tq the Carrier Corporation. is approximately rive par cent lower

than tU theoretict& values r-4.-ea tnw t in the rrth-c1i chart of" tt* ARIUM

I ] Guide and Data Book (Ret. i).

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2.2.1 Tubing

i I Plastic tubing lengths from 450 to 50 feet in increments of 50 feet were

tested at flow rates from 1.00 to 4100 SCFM (standard air) with the discharge

end of the tubing unrestrained (see Figure 6).

i Five high impact strength (Type II), untreated (Finish 1) tuuing specimens

were tested. Of these samples one was low slip* (Grade A), three were medium

slip (Grade B), and one was high slip (Grade C). The diame.ter is 19.75 + 0.25

jl inches, and tue thickness 0.004 (4-mil) + 0.0008 inches. The samples were

furnished by the Sinclair-Koppers Company, Inc. and the National Poly Produicts,

t Inc. Thin gage polyethylene films are classified as follows (Ref. 4):

L Type I Normal impact strength.

Type II High impact strength.

Grade A Low slip.

Grade B Medium slip.

SI Grade C High slip.

Finish 1 Untreated.

,I Finish 2 Treated.

ii 2.2.1,1 Duct Adaptor

l AftEr determining the friction loss ot' a plastic tubing specimen,

i the duct was %tQted vlth the duct adaptor attached to the free-end (see Figure 7).

*The test apparatus arid methods t',r determlnrWi the irpact, strenght it and slip

f!kinet~c cooEfi'cint of rricti~n) are preotnted in Federal SpecificationL-P-378. Finish 2 filLm is treaied t... aj e printinfý ink to adhere.

i|-_. LtIatIEAL AMIEPICAr- AEUEARNC~ OI;lVllISIO

Figure 6 TEST OF THE TUBING WITH THE END UNRESTRAINED (FREE AIR DISCHARGE)

Fi•.,urc 7 TEST OF THE TUBING WITIH THE DUCT ADAPTOR

GENERAL AMERICAN fIEUEAiICH ODVIBION

9

II

The purpose of' this test was to determine the friction 1bss of the system with

and without the duct adaptor for those duct systems where its use is optional.

"2.2.1.2 PVK Application

After determining the friction loss of plastic tubing specimens these

same specimens were attached tc a calibrated Civil Defanse Package Ventilation

Kit ventilator and the power input was measured (see Figure 8). Knowing the

wattage input to the system the air flow and pressure drop were determined from

the fan motor performance curve (Ref. 5). The air flow obtained by this meethod

agreed within three percent of the values obtained with the test set-up.

Therefore, the friction loss for tubing and fittings determined herein can te

applied to the Civil Defense propeller-type ventilator as s-pecified in MII-V-

40645.

I

I

3 Figure 8 PVK-DUCT TEST

IGENERAL AMERICAN RESEARCH OIVlIlON

1 10

2.2.2 Elbows

The friction loss of all fittings with 100 feet of straight tubing on the

downstream end of the system were ccmpar,-d tc each other. Testing with a duct

on the discharge end cf the elbcvs was necessary tc filly inflate the fittings,

and the results are thereforE only applicablt- tc fully inflated fittings. The

best factory fabricated and shelter fabricated elbows were then further tested

with duct lengths of 100, 200, and 300 feet to determine the effect of static

pressure on the elbow pressure drop cr equivalent duct length (EDL).

2.2.2.1 Factory Fabricated Eltows

A preliminary specification f,_r flexbtle: plastic elbows which might

be used in constructing a sh-lter ducc system to b- attached to a portable

ventilator was sent to eight fabricators. This specification is included aR

Appendix B. The temperature range, flow ra-e, and inrtrnal pressure were

specified to incorporate the most adverse conditicns expected during storage

and operation. Cost quotations were: requested for the fabrication of elbows

in seven configurations with varying centerlir. radii from 20-inches to 60-

inches. Table II shows the relative prcduction costs of' the 20-inch diame( r,

90-degree, smooth radius elboh with a 4C-inch centerline radius.

The majority of fabricators preferrti the us.- of polyvinyl chloride

(PVC) because it is easily heat stalrd and less expensive. All manufacturis

indicated that the smooth and miter -lbows were the siffpl~st and least

expensive to fabricat+ in. tlexiblt ;Iastir, 7Th- co -f tlii miter elbow

was essentially the same as a inrc17 '-!cw with a cr-nterline radius of 20

GENERAL AMERICAN RESEARCH OIVISION

3I

Table II

I- Costs of Smooth Elbow

I Manufacturer Material Thickness Quantity

mils 500 350,000 700,000 1,050,000

1-- Polyvinyl

1 Chloride 4 $2.00 $1.28 $1.26 $1.24

- Poly-2 ethylene 4 $15.35 $3.00 $3.00 $3.00

Polyvinyl3 bloride 8 $3.10 $2.75 $2.60 $2.55

X PolyvinylS4 hloride 4 $2.08 $0.43 $0.38 $0.37

*Outside seams of full production units would not be trimmed.

I inches. Therefore, 90-degree smooth and miter elbows of 4- and 8 -mil thick PVC

--I with centerline radii of 20, 30, 40, and 60 inches were selected for testing.

A wire-reinforced elbow was also tested (see Figure 9). This elbow was

S constructed by inserting,- heliý.al coil of 0.072 inch.dia. tinned music wire

i inside u straight length of four-mil, 20-inch diameter, polyethylene tubijn,

The wire was taped to the inside of the duct every 90-degrees around t~hF

periphery of the tubing, and the distance between hoops was six inches.

2.2.2.? Shelter Fabricated Elbows

The shelier fabric-ated elbows that were t1estel were ,ri,-d-tucked,

I 3-pi .', and packi.,1,,, boxes taped t,. ier. The h - w U '20-

strumted by f'orring tucks )r p.1eat. l; ', r .'e s!ide &t he W'.d,' •wj aping the

I tu-.-s s that a gradual rad.iu, o1 ,urva, w.c ! eve l.p.I ( 'ee FiAr eure !,

SGENEIAL AMERICAN RESEARCH OIVISION

Figure 9 WIRE-REIUORCED ELBOW

Figture LO HAND-TUCKED ELBOW

CUPUESAL. AMURICAP• *UUUAmC Otvsaloe@

I!

The excess material inside of the duct, formed by the tucks, was placed down-

stream to reduce the resistance to air flow. This elbow is difficult to

.i construct, and in most cases requires a relatively large floor area when

inflated as compared to the other elbows.

mI A three-piece elbow was fabricated from polyethylene tubing by cutting

two 32 x 16-1/2 x 32 inch triangular-shaped sections 58 inches apart (see

Figure 11). The tubing was taped after overlapping the downstream seam

(relative to the direction of the air flow) approximately one inch. This

provided an elbow with an approximate centerline radius of 60 inches (see

II Figure 12). This elbow is easily constructed with a template.

1 A rigid elbow was constructed frocn a corrugated fiberboard box (see

Figures 13 and 14) and teýted. The packing box elbow, especially one less

I than 90-degrees, is very difficult to construct and requires materials which

in many cases will not be found in shelters.

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CIENENAL AMUNICAN NEUKANCS.4 OIVIUION

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GeFYPIA AMRICA ORBSURCH IVIICH

SECTION 3

RESULTS AND ANALYSIS

3.1 Tubing

The friction of air in straight polyethylene tubing for lengths from 50

to 450 feet are shown in Figure 15. These curves are bas0A on a least squares

regression of the test data as shown in Appendix A. The standard error of

estimate; i.e. the mean of the square of the differences between the data and

the fitted curve ranges from 0.007 inches of water gagt (iwg) for the 150 foot

length to O.02 iwg for the 4oe foot length. As indicated by the data presented

in the Appendix, the low slip zpecimen has the least friction loss for all

lengths except the 50 foot length. It was expected that this specimen would

hare the highest friction loss, and the high slip specimen the minimum friction

loss. It is felt that an insufficient number of samples were tested to establish

if friction loss can be correlated to slip since orly one lot of the low and

high slip specimens was uzed.

Figure 15 and Table 1II show that the pressure drop for the last 50 feet

of tubing in a duct system is from 1-1/2 to 3 times as great as that for duct

elsewhere in a system. As shown in Figure 6, page 9, the last 50 feet of

tubing in a duct system is not completely inflated due to the weight of material

and decreased static pressure in this part cf the system. The air velocity

in a partially deflated duct is greater than that in an infl&ted duct since

the cross-sectional area is leýs the.n that o' a ful.Ly inflated or circular

duct. Since the pressure drop due to frictlon is approximately proportional

to the vel.)city squared, the increase vel9ci!.y in partially inflated

UeN1,,AL AMERICAN ,•COARCM o,0,1,oA.

- --- - .~ -

I

Ij duct results in an increased pressure drl_. iii this section of duct. As the

flow -,te increases, the length of uninflated tubing in a system decreases.

As shown in Table lIT the friction loss for the polyethylene tubing other than

the last fifty feet in the system is approximately proportional to the length.

1 For example: at 1000 scfm the pressure dr-p increases 0.007 iwg (range:

0.006 to 0.007) for every fifty feet additional tubing; at 3000 scfm it

increases 0.049 iwg (runge: 0.047 to 0.05].) for the same length increments.

The friction losses of polyethylene tubing and sheet-metal ducts are also

compared in this table. In general, the friction loss of inflated polyethylene

I tubing is less than that fcl the same diameter sheet-metal ducts, whose pressure

drop is directly proportional to length. At 1000 scfm the friction loss of

inflated plastic Lubing is 0.007 iwg per fifty feet as compared to 0.008 for

the sheet-metal duct; at 3000 scfm the friction losses of plastic tubing and

sheet-metal ducts are 0.049 and 0.065 iwg per fifty feet, respectively.

I A mathen-atical expression derived from the least squares fitted curves of

a the data (see Appendix A) is:

p 1.915 x 10-6 [q1.349 + 0.01006 1) Ql. 8 33] (1)

I.where:

P = static pressure loss, inches of water gage

"IQ = air flow rate, standard cubic feet per minute (scfm)

L = tubing length (for lengths of 50 feet and longer)

The solid curves in the Appendix are based on the test data, while the dotted

Sportions ef the curves were generated with Equation 1.

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GENRA A'ERCA REERH0VS

3.1.1 Duct Adaptor

The P•K includes a Duct Adaptor which is uved to seal the plastic ducting

to a window or doorway opening in, a shelter. This adaptor was tested with

plastic duct to determine if it could support the discharge end of the duct,

and thus reduce the high friction loss o; the final fifty feet of tubing in

a system. The Duct Adaptor increased the static prest:ure loes through the

duct system since a negative pres-cure occurs upstream of the adaptor. This

additional pressur- loss results from the converging and expanding air strean.

through the reduced flow area (see Figure 7, page 9), Therefore., the Duct

Adaptor specified for the Kit (YMI1-V-LO64c5) does not include legs., and is

intended for use in windows, doorways, or partitions cnly. When the air

supply for the shtiter enters the duct exit opening, or other r:Earby air

supply openings, the duct should extend at least 35 feet from the building,

and should not include the Duct Adapto:." (free air discharge).

3.1.2 Condition of Duct

Creases are formed in tht tubing during fabrication by rolling the tubing

on a cylindrical core. Tests with these creases in both the horizontal and

vertical positions produced the sam. static pressure losses. The tubing that

was walked on and crushes, howevtr, did indicate a decrease in static pressure

loss and less "whipping" and "flutter" at the discharge end. Ripples are

formed in new tubing when it is firsr irflated Tee Figure 16). After the

tubing is crushed, wri.nklti, aýJ g•nerally abused, these ripples diminish,

thus accounting for tnr- Ic,:, -as,- i. static ý :sui. .c-ss, s.

ULNERAL AMERICAN RESEARCH DIVISION

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3.2 Elbows

Each of the factory and shelter fabricated candidate elbows was tested

by fastening it to the test stand and taping a 100 foot section of polyethylene

duct to the downstream end of Uhe elbow to assure that the elbow is fully

inflated. The pressure losses measured for these systems are presented in

Figure 17. Based on the results of this comparison of factory and shelter

fabricated elbows, a series of tests were conducted to determine the ien:gth of'

straight duct equivalent to the pressure drop for the recommended factory and

shelter fabricated elbows when fully inflated. These tests evaluated the

elbows with straight lengths of tubing. The tubing was attached directly to

the elbow by overlapping approximately one inch of the end of the elbow and

t. ,ing the seam. When inflated these elbows produced a total curvature or

bend of approximately 110 cegrees. This phenomenon is caused by stretching

of the plastic material due to the elbow internal pressure. Since the surface

at the outer radius of the elbow contains more material than the surface at the

inside radius, the effect of the stretching produced an angular bend of more

than 90-degrees. Prior to recurding data, all elbows were inflated and trimmed

to form a 90-degree angle. No attempt was made to determine the equivalent

duzt length for partially inflated elbows.

Of' o AMUPIOCAIU1 SUlUEimCH OIVotUUON

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with 100 feet oflow slip, NPP tubing

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F.Ieu- 1ý PRESSUTE DRCT XMYARION OF ýKý-V&sREE ELBMZý

GENERAL AMIEnICAPY IM606464CO-4 0jVt8jCN

3.2.1 Factory Fabricated Fibotws

The elbows with thim lowest pr-,ssur- lo~ss-s art, factory fabricated smooth

radius elbows "see Figurte 17). F'or a giv~-r configuration. tht:m elbows fabricated

from four-mul plastic had low-.ýr prt.--surt- lo~s.s-ý than t~hose fabricated from

eight-mil plastic. The change in prt-:ssture los;s with c-ernt-erldirje radius decreased

as the centerline radius approached 60 inche-s. rh- lbows with ctnterline

radii of ~40-inches arid 60.inchims have neýarly ident~cal pressure losses,

indicating that the trade-;-off point fo7r c#-nterlinc radzius vErsus pressure loss

is approximately 40L inches. Increasing thi- cent,ýrlin-. radius beyond this point

provides only a minimal decre-ase in pr isvr,ý loss, and requires considerably

more shelter floor arta when; inflatt-J,

The mitered elbow had a considýýablt- prf:ssure- drop, even greater than

the shelter fabricated three-PIi~-Ce - lbicW, becauste of the extreme flutter and

vibration which developerd. Figurt- 18 is "stop-action" photographs of thr*

miter elbow illustrating the amiplit-.AdA -,f the pu.lsation in the tubing an"! elbow.

The wire-reinforced elbiow (sF~igiirý- 9,pagf-' 131 dev:i-oped excess!Ife

pressure losses. This tlbow had to tt aktare t Plow rate-s above 2000 cfm

to keep it from straightening out, W~thr thtm rý.ctraint, th- ~-1bow tended to

kink into a short. radius r-lbow' such as a miter ~1c.Thi instability

resulted in. the high preýsstur,: 'o~s

GENERAL AMERICAN REBEAPRCH CIVrnION

7-I.A

IvPLT : IE LO

Il~ A f4~CNf~L-fC 1060

The four-mil polyvinyl chloride 40-inch smooth radius elbow is the best

factory elbow w"en cosidering pressure drop, space requirements, material and

-cost. Figure 19 shows the results of further rests performed on this elbow.

The soliA iVnes show the pressure losses for the elbow with straight lengths of

tubing attached to the downstream side, the broken lines show the pressure losses

for the straight lengths only, It can btý seern that the equivalent length of

stra-,ght tubing for the -O-inch smooth radius elbow is approximately 50 feet

when fully inflated. For the elbow to be fu.ly inflated fifty feet of straight

tubing must be on the downstream side.

3.2.2 Shelter Fabricated Elbows

Of the shelter fabricat•1 =-bcw ( •ur. -C', thý- three-piece elbow

results in the least pressur._ loss. The elbcw made from packing boxes produced

the largest pi essure loss. This elbow was extremely stable at all flow rates;

howeverthe exit and entrance losses of' the air -tream in the plenum-like

box produced the high pressure loss., The best hand-tucked t-!bow resulted in

pressure drops considerably higher than those shown in Figure 17. Since the

results were erratic (due to the elbow beng unstab_ý n! curve is presented.

Since the three-piece elbow has the least r(-ssure lost this elbow was

further tested with 100 t 20, and 300 fet of tubing (set Figure 21). it can

be seen that thepressure loas of the th.,--piect titovi with a centerline

radius of 60-inches is equivalent t, 90 f-ct of straight tubing when 'ully

inflated. For the elbow i.o v- L-l- :i fldt-] :'-v f--t of straight tubing

must be on the downstream Sl*:

IGEINER~AL AME£RIC:AN R•IUEARCH OIVI9ION

.60

55 --5

1.550(SEINGAPP INCILAIR S-MKOLPER)

II'.45 F

4.+4

.. 35 ....

II~.0IV

It.25

(a ----- 7F7

vI I

Three-piece, 60* Radius, ElbowI

Packing Box Elbow 1

Hand-tucked ElbowI

Figure 20 SHELTER FABRICATED ELBOWS IN OPERATION3

OWNRINAL AMERICAN 080EAU0C4 OIVtSOrv

31

DUC LaGI4 oil

AI2LO 0

TUIG SNLI OPRMEIMSI

(SE PEOXA IsL0tilI Ilo RIe IM 1~ 1.011 ILB C Fttll

I 32il

SECTION 4

SUMMARY AND RECOMMENDATIONS

The friction losses of the 4-mil polyethylene tubing specified for the

Package Ventilation Kit, MIL-V-4O645, have been determined (sef- Figure 15 and

Equation 1), and have been incorporated into the FVK rating (Ref. 6). Fully

inflated 20-inch diameter plastic tubing has about three-quarters of the

pressure drop of sheet-metal duct. However, the last fifty ftt of a plastic

duct system which is not completely inflated has l-i/2 to 3 times the pressure

drop per foot of fully inflated plastic tubing. The result is that for duct

systems over 100 feet long the pressure drops for sht-:,t-metal and plastic

tubing are approximately the same.

The Duct Adaptor supplied with the PVK. should oe used to prevent re,.ir*.

culation in windows and doorways when the duct system terminates there, ind Iwhen necessary in corridors and partitions for developing systems which

control the flow or distribution of air. The Duct Adaptor should not be

used elsewhere, such as the end of the duct outside of a buildirg, since its Iuse increases the system pressure drop.

The smooth 40-inch radius plastic elbow is the best of the factory

fabricated elbows, This elbow when fully inflated results in a pressure

drop equivalent to 50 feet of straight tubing. For thte elbow to be fully

inflated at least 50 feet of tubing must be on its downstream side. Since.

this elbow must be cut at 75-degrees whin uninflateA so that the resulting

inflated elbow is 90-degrees, it is rt_-c,mmtrjd-d that ",Figure 8 of MLL-V-

GENERAL AMERICAN RL•SARCH UIVISION

S- -n

o40615" be modified as shown in Figure 22.. The cuffs have been rem-wed since

Sthey are of no value for taping the tubing to the elbow, and in most cases

j produce wrinkles and dis'-ortion. Since polyvinyl chloride material is easily

heat sealed it is recommended that tris material be specified in paragraph 3.7.3

1 of MIL-V-L0645; therefore, the second sentence of this paragraph should read

as follows:

- "The elbows shall be !'abricated from 4-mil thick polyvinyl chloride

h or type II, grade C, finish 1 polyethylene conforming to Specification

L-P-378 with a minimum flat dimension of 31 inches."

The most efficient shelter fabricated elbow is the 60-inch radius three-

piece elbow. This elbow when fully inflated produces. a pressure drop

equivalent to 90 feet of straight tubing. For the elbow to be fully inflated

3 at least 50 feet of tubing must be on the downsticam side.

Factors that should be considered in the selection of elbows for use in

shelters are the simplicity of assembly, floor space required when inflated,

"3 stability in operation, ana cost. Assembly of the factory fabricated elbow

in a duct syLtem is a simple matter of cutting straight lengths of tubing

at the appropriate length, inserting the elbow, and taping the components

* together. Any angle between zero and ninety degrees can be obtained by

cutting the elbow at the angle desired. The shelter fabricated elbow can

be fabricated from materials in the PVK, and the required number of 90-degree

elbows can be fabricated to develop a suitable ventilation duct system for

any shelter. The three-piece, 90-degree, elbow can probably be constructed

by the shelterees with a template and instructions; however, fabrication

( GENERAL AMERICAN RESEARCHl OIVIUIOJ

34

73

It

�E..

I1III.

I-,

'IE4 I'U

CJ I0dp

.3' 1c�J D's

C,, 1+1H -

IIII

SENUmAL AMUPUCAN *UACE D�VIUSON 335

of an elbow with angles other than 90-degrees would most likely be difficult

and confusing. Therefore, it is recommended that:

1) One factory fabricat•ed elbow be furnished with the PVK. One

elbow should-satisfy the majority of shelter duct systems.

2) A 90-degree elbow template should be included with the PVK

for those systems requiring more than one elbow. If a system

requires elbows with an angle less than 90-degrees a factory

fabricated elbow should be cut for the desired angle, thus

eliminating most cases of shelter fabrication of an elbow other

than 90-degrees.

The equivalent duct length of any plastic tubing system can be determined

by adding the total length of straight tubing plus the number of elbows times

their respective equivalent duct length (see Equation 2) -- 50 feet for the

factory fabricated elbow and 90 feet for the shelter fabricated elbow.

EDLs = L + 50 Nf + 90 N (2)

where:

EDL = Equivalent Duct Length of the system, feets

L - length of straight duct in the system, feet

Nf - number of factory fabricated elbows, dimensionless

N = number of shelter fabricated elbows, dimensionless

The pressure drop of these systems my be determined using the following

equation.

6 1.349 EDL ) 31 (3)

RPNENAL AMIAI *USUAPCH OIVlIe•36

where:

AP a static pressure drop, inches of water gage

- air flow rate, standard cubic feet per minute (scfm)

FPDL - Equivalent Duct Length of the system (for lengths of 50 feet8 and longer), feet

Equations 2 and 3 have been experimentally verified for straight tubing,

and for elbows located anywhere in a duct system except within 50 feet of the

discharge end. Future tests should be performed to verify the generality of

equations 2 and 3 to a system with the elbow(s) partially inflated (within

the last 50 feet of a system). Tests on other diameter plastic ducting and

ducting fabricated from different thicknesses of plastic should also be per-

formed to establish a general relationship for plastic duct pressure drop in

order to evaluate the performance of shelter ventilators of other diameters.

37

REFERENCES

1. B. A. Libovicz and H. F. Behls, "Shelter Package Ventilation Kit",prepared for the Office of Civil Defense under Contract OCD-PS-64-22, OCDWork Unit 1423A, General American Transportation Corporation (GARD Report1244), Niles, Illinois, October i965.

2. National Electrical Manufacturers Association (NEMA) Standards PublicationNo. FM1-1955, "Electric Fans", 155 East 44th Street, New York, New York.

3. ASHRAE (American Society of Heating, Refrigerating and Air-ConditionitigEngineers) Guide and Data Book, 1965 and 1966, New York, Chapter 31,Figures 2 and 3, PP. 562-3.

4. Federal Specification L-P-378, "Plastic Film (Polyethylene Thin Gage)".

5. Libovicz, op. cit., Figure 36, p. 65.

6. Libovicz, op. cit., Figure 31, p. 55.

INnLAeA ,•s•:•ovmDI9Ia m m m mun n In n

IUIIIIIII

APPENDIX A

I3 TESTM�A,

II

IIII

UUP��AL AMaS@AF. *EUS*S@w mv.s.o.

39

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GENERAL AMERICAN RESEARCH CIVIVION

45

a I4--.

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OUNERAL AMEUSICAN 049UEARCH OIVOIdON'48

8

APPEINDX B

SPECIFICATION USEDFOR DETERwMINN cos:-,

OF FrINGS

UmUmWL• ASWNAN m~Sm~mtow omvmsu1oi4

II Spec. No. 1278-1

Date: 13 April 1965

3 General American Transportation Corporation

S2ecification for Plastic Duct Elbows1 1. S cpe

A study is being conducted to determine the type, quantity, material,and configuration of plastic duct fittings which will be required in aportable Package Ventilation Kit suitable for Civil Defense fallout shelters.At present it is anticipated that at least tt':ee 900 elbo'is or three 45*elbows will be required per kit. This study will include fabrication ofvarious 45e and 9Q0 elbow confifurations with subsequent tests and analysisof each configuration. Selection of the optimum zlbow will be based onefficiency (low pressure drop), stability, and production costs. A productionrun of the package ventilation kit will be on the order of 350,000 units inwhich at least three of the selected elbows will be supplied per unit.

3 2. Requirements

2.1 Description

The elbows are to be fabricated from 4 mil (.004) niini•aum pial"1c filmsuch as polyethylene or polyvinlychloride, etc. with a 20 inch ncrrnialdiameter (equivalent to tubing 31 x .004). The maximum stati pressurewithin the elbows will be 1.0 inches W.G. The maximum air velocity withinthe elbow will be 2000 feet per minute. The elbows must be capable ofbeing stored (but not necessarily operated) at ambient temperatures of-60*F to 120*F and relative humidities of 0 to 100%. Operational temperatureof elbows in a ventilation duct will be approximately 85*F. The cuffs ofthe elbow will be assembled to straight lengths of polyethylene tubing31 x .004 by means of a coupling to form the ventilation duct. Materialfor the elbows must be flexible, unsupported plastic film in natural colorand odorless. Type, grade, and finish of plastic material can be specified

* by the fabricator. The method of sealing or bonding the seams is left tothe discretion of the fabricator.

2.2 Elbow Configurations

Seven elbow configurations under consideration are shown in zrawl-ti gnumber Spec. 1278-1. Each configuration is dimensioned In respect to aradius R, nominal diameter D, and a cuff length C. Preproduction modelsof each configuration are required for testing and will have the followingdimensions.

C a 4"; D -20"; R = 20"C a 4"; D 20"; R 0 30"

4"; D 20"; R a 40"C w 4"; D 20"; R a 60"

1 e~aft L AMGIClAN IIN.ARN@ DIVIGIOS

Spec. No. 1278-1

900 3-piece elbow (4 elbows in total)

C = 4"; D = 20"; R = 20"C = 4" D = 20"; R = 30"C 4"; D = 20"; R = ho"C = 4"; D = 20"; R = 60"1

9g0 5-piece elbow (4 elbows in total) [C = 411; D = 20"; R = 20"C =41"; D = 20"; R = 30"-C =4"; D = 209"; R = 40C =- 4"; D = 20"; R = 60"

90* mitered elbow (1 elbow in total)

C = 6"; D = 20"1

45° smooth elbow (4 elbows in total)

c, = 4": D = 20"; R = 20"1C = 4"; D = 20"; R = 30"C = 4"; D = 20"; R = 40"C = 4"; D = 20"; R = 60" Ii

:-05° 3-piece elbow (4 elbows in total)

C = 4"; D = 20"; R = 20"C = 4"; D = 20"; R = 30'" -

C = 14"; D = 20"; R = 40"c 4"; D = 20"; R = 60"1

450- mitered elbow (1 elbow in total)

C 6"; D = 20"

The dimension: D is nominal and is equivalent to the diameter of extruded Utubing 31" x .004.

3. Quantity

Preproduction elbows for testing purposes will consist of one elbowper size per configuration or a total of 22 elbows. After testing a cost versus -performance analysis will be conducted to determine the optimum elbow configurationand size. A production run of the selected elbow will then be made in quantityof 500 units. A follow-up production run will consist of either 350,000, 700,000,or 1,050,000 units to be fabricated over a two year period. Cost estimates of [preproduction elbows as well as estimates of each size and elbow configurationin quantities of 500, 350,000, 700,000, and 1,050,000 should be submitted by I"the fabricator.

GENERAL AMERICAN RESEARCH DIVISION

51

low" AWN G- F -i -

'hii

In.

41)2

) Mi

S in

dl

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00 W

GFIERA AMRCA EEACiVSO

'3 3 2,,5W

IJNCIA2$I6FIED

DOCUMENT CONTROL DATA - R&DfSeaaefty .Ie..Li1eatla, W1 tgpI. e4* of abuenceOWtowsid anndeaad uatn amunt be antmen attn w N.oveoait apoai Ia clasaaffled)

I. ORIGINATI:4 0 ACTIVITY (Cau~t.~t aulber', a RULPOR7 SECURITY C LABRIFICATION"

General American Transportation Corporation I UN~CLASSIFIEDI 7i449 North-Natchez Avenue [z.6mouP

Niles, 1P'inois _______________g S. REPORT Y!Ti.C

Friction Loss in Flexible Plastic Air Duct-

< 4. DECIPTIVE NO-Tag (T#111 of tgmlt a" 610111011 dot")-

Neveril., R~obert B.

Behls, Herman F.

__._REPORT__________7a__ TOTAL NO. OPPA 7b. No. OP REFS

Ib H Pont-40) (Anly adwrnue mbs that may be aselndmo

~1 10. AV A IL ADILITY/LIUITATION NOTICES

Qualified requestors may obtain copies of this report from DDC.'Distribution of this report is unl imited.

I1I. SUPPL EVEN TARY NOTES 12. SPONSORING MILITARY ACTIVITY

Office of Civil DefenseF I Departmrent of the Army_____________________j Wav-hingtor, D.C. 20310.

IS. ANSTPACT

The friction losses for 20-inch diameter, 14-mil t hick, flexible polyethylene-tubing and plastic elbows are presený;ed in this report. This type of ducting

L is intended for use with the Civil Defense fallout shelter ventilatorspecified in MIli-V-406L45, (U)

L

[ DD I JAN$ 1473 UNCLISS rFTHESecurity C!flsaiflcation

UIMCLSSLIEiDSecurity ClassificationLNKALN *

KEY WiROS- - -

ftor- Wi' fOLS Wi' no' WT

CIVEL L"F'9ENSE SS?,F4V'S -r1Z-F FALLOU7 ST~UiTIFFSSPECIF [CAT FON'SCOOL~iGG & VENTT 1IAýTING EQUIPMENTVEN'TEIATIGIN

E-IRONMENT IMATTIB ALSPIASTICS

INSTRUCTIONS

I. ORIGINATING ACTIMVTY Enter the name and address io AvAILABILIT V/LIMITATION NOTICES: Enter any lrn-of the contractor. subcontractor. grantee, Department of De. -iain oni further dissemination of the report, other than thosefease activity orote organization (corporate uhr sunth. reort. 0ato)Isig mpsech by security classification, using, standard statements

2& EPOT SCUITYCLASSIFICATION: Enter the over. (1) "Qualified reqwvesý may obtaini copies of this91 security classification of the re'port. Indicate whetherance with appropriate security regulations. (2) "Foreign announcement and dirsmemination of this1

2b. ROU Auoma'- dwngadig i upeifid ~DeDreport by DDC is not authorized."

-rective 520010 and Armed Forces Industrial Manual. Enter (3) IOU. S. Govermnt agencies may obtain copies ofthe grouli numb~er. Also, when applicable, show that optional thi report directly from DDC, Other qualified DDC

markings have been used for~ Group 3 and Group 4 -as author. users shallI request 'through

3. REPORT-TITL- Eater the complete report title in all (4) IOU. S, military agencies may obtain coie of thiscapital letters Titles in all cases should be unclassified, report directly from DDC. Other qualified usersIf a meaningful titlv cannot he selected vwithout classificap *Wti request throughtion, show title claisit'catiou In all capitals in parenthesisimmediately following the title.________________

4. D)ESCRIPTIVE NOTES: It appropriate, enter the type of (5) "All distribution of this reprt is controlled. Qual-report. eg.. Interim, progress, summary, annual, or final. Iifid DDC users shall request through

Give the Inclusive dates when a specific reporting period Is

5. ATHO(S):Entr te nae~s of uthr~s as how on If tAe report has been furnished to the Office of Technicalor In the report. Enter last name, first name, middle initial. casv, Deps actmadente ofe Comrice, if kowr.sl otepbimIf military, show rank and branch of service. The name of ctehifatndnerhepcifkosthe principal author is on absolute minimum requirement. IL SUPPLfEMENTARY NOTES. Use for additional explana-6. REPORT DATE. Ente~r the date of the report as day, tory notes.month, year, or month. yeas If more than one date appears 12. SPONSORING MILITARY ACTIVITY: Enter the name ofon the report, use date of publication, the departmental project office or laboratory sponsoring (pt ?I

7a. TOTAL NUMBER OF PAGES;- The total page count ing for) the research and development. Include address.Ushould follow normal pagination procedures, Lo., enter the 13. AEUSTRACT; Enter an abstract giv'ing a brief and factualnumber of pages containing information, summary of the document indicative of the report, even though

it may also appear elsewhere in the body of the technical re-76. NUMBER OF REFERENCE&: Enter the total number of port. It additional space is required, a continuation sheetreferences cited in the report. shadl be attached.I&a. CONTRACT OR GRANT NUMBER. If apprwpiate, enter It is highly desirable that the abstract of classified re-the applicable number of %&e cor2ract or grant under which Iports be unclassified. Eat-h paragraph of the abstract shallthe report was written, end with an indication of the military security tblassificationSb, 8c, & Gd. PR~OJECT NUMBER: Rnter the appropriate of the irformation in the paragraph, represented as (TS), (S).military department kdontification, such as project mumber. (C), or (U).subproject number, system numbers, task number, etc. There Is no limitation on the length of the abstract. How-9.. ORIGINATOR'S REPORT NUMBER(S): Enter the offi. ever, the suggested length is from 150 to 225 we-ds.cial report number bi' which the document will be identified 14. KEY WORDS: Key words are technically meaningful termsand controlled by the, originating activity. This number must or short phrases that characterize a report and may be used asIbe unique to this Mejomt index entries for cataloging the report. Key words must be

96. OTHER REPORT NUMBER(S): If the report has been selected so th.: -urity classification is required. Iden-

assigned any othe report numbers (either by the originator tiers, suciý as oe, it model designation, t.rade name, mili-or by the aponeor). also enter this number(5). tary proj,,ct code name, geographic location, may be used as

key words but will be followed by an indication of technicalIcontext. 'rhe assignment ol links, rules, and weights inoptional.

UJ

Sacilly Classification

(D 1.421

-H ) (DW H ( )

4-) r HO 4:) "4 (aO

r-4r- (A 4-

N- aH~- 'I4 - rlH0 ~OZ

U . E-4 4. 400 4-)4-30W

V 4 10r 4. _2*f-rE2 -4

"EI IHr 940-0 0 ri4i4 F4 ca~00 ~O3.'

4X) 0*'4 cu# HQ0 V(

VCI 2G F-4vo a 14 4)H t 4.).e K'E1HH+

m to 4. 0 044C f+ C'I 0 00 P44 C-w 0 W~ 4.) rO) v.d 4) 4,~. -1).024 H M2H N1~. m0'

4+)'U 0H0.c 0 .V, -4 U3cuco 0 o > CH.Q 2 14k34 CO. \ 00 4 -T J\ t-r4 04I:" )"

~H 43t.UN0 4GJ V.r t ~ J (a toC H 4-) > UN W r4 r4

0 -1P40 O " P f+G43

1.4 U2P) 1.4 C12+4) W) o )0)' Jv) H HO P4 H 1 HOI4 04 4 ) aE.-or- 4 %-r a * r.4~ Iai M

V4 4J 0E- 2) 00

CI2H H

CD0 00 P

*- 0Q V4I H(O H (D 0 04. -H4 0)

4- * ~ O r4 I 0

H)

0

Prepare6 forOffice of Civil Defense

Department of the Army, OSAunder

OCD Work Unit 1423ASRI Subcontract No. B-70925(4949A-28)-US

SUW_ -LR~ yOF

RESEARCH REPORT

FRICTION LOSS IN FLEXIBLEPLASTIC AIR DUCT

GARD Report 1278-2 October 1965

by

General American Transportation CorporationGeneral American Research Division

Environmental Research GroupNiles, Illinois

REVIEW NOTICE

This is a summary of a report which has been reviewed in the Office of CiviDefense and approved for publication. Approval does not signify that thecontents necessarily reflect the views and policies of the Office of CivilDefense.

GENUR\L AMEJRICAN RESEARCH OIVISION

F~.vr~:~ ~AKW~'tl,4A-`TIQ.N KITS IN OPERATION

I1TRODUCTION

A Package Ventilation Kit (PVK) was developedI for use as an inexpensive

method of exhausting stal.e, hot and himid air from fallout shelters (see

Figure 1). This ventilator Is intended for use with flexible plastic duct

systems (see Figure 2) and, therefore, flexible plastic tubing and fittings

are supplied with the Kit. The objectives of this program are to determine

the friction loss of flexible tubing and fittings, and to recommend the best

fittings, based on cost and pressure drop, for use in fabricating shelter duct

systems.

Fi.3ure 2 PYK DUCT SYSS71M

B. A. Liboviez '11. F. Bels, "St~heiter Pat:-a. Ventilation Kit", prepcred

ror the Offtice ;f Civil Litfenae under Cct.ract OCP-PS-64-22, OCD Work Unit.

Illinois, ioiber1

mHBM MAL AMOOMSO AMMNW OAW NVUS@

TEST PROCEDURES

P" .aratus.--The test apparatus consisted of an 8,000 cfi centrifugal blower

connected by a flexible wire-reinforced cloth duct to a 47 foot long, 20-inch

diameter- test stand which was fabricated from 24 U.S. Gage, zinc coated steel

spiral conduit duct with 6 inch seams (see Figures 3 and 4). The design of the

test stand is based on recommendations of the National Electrical RManufacturers

2Association. Air flow rates were measured with a 14-inch diameter aperture

sharp-e•dge orifice plate which was calibrated with a pitot tube five feet

upstream from the orifice. Two air straighteners were located approximately

14 feet and 28 feet upstream of the orifice plate to reduce turbulence. A

piezometer ring was located 14 feet downstream from the orifice and 5 feet from

the end of the test stand. Inclined manometers were used to measure the pres-

sure drop across the orifice, and the static pressure drop of the test specimens.

Methods.--The specimens were first taped to the test stand. The blower was

adjusted to provide the desired flow rates, and the static pressure loss and

flow rate (o'.ifice differential pressure) were recorded. Barometric pressure,

dry-bulb temperature, and wet-bulb temperature were recorded before each test

to provide the flow rate correction factor to standard air (P = 0.075 lbs/cu ft).

The tare pressure drop of the test apparatus, i.e., the presbure drop caused by

the 5 foot length of spiral duct between the plane of the measuring station and

the plastic specimens, was subtracted from the test data after its correctio.i to

standard air.

2 National Electrical Manufacturers Association (NEMA) Standards Publication

No. FMl-1955, "Electric: Fans", 155 East 44th Street, New York, New York.

GENERAL AMERICAN REDEARCF 0,1VISION

4

Tubing.--Plastic tubing lergths from 1450 to 50 feet in increments of 50 feet

were tested at flow rates from 1300 to 4100 SCFM (standard air) with the

discharge end of the tubing unrestrained. Five high impact strength (Type II),

untreated (Finish I) tubing specimens were tested. Of these samples one was

low slip* (Grade A), three were medium slip (Grade B), and one was high slip

(Grade C'. The diameter is 19.75 + 0.25 inches, and the thickness 0.004

(4-rail) + 0.0008 inches.

Elbows.--The friction lcss of the fittings listed below were tested with 100

feet of straight tubing on the downstream end of the sy3tem and the results

were compared to each other. Testing with a duct on the discharge end of the

elbows was necessary to fully inflate the fittings, and the rpsults are

therefore only applicable to fully iflated fittings. The be:.t factory

fabricated and sheltcr fabricated elbow,- were then further tested with duct

lengths of 100, 200. and 300 feet to determine tho effect of static pressure

on the elbow pressure drop or equivalent duct length (EDL).

K•. t• • h•Lt, St• Material

1F-i•1C&UnM Ma Mrs ___ " Table IM INtily 60 smooth Madlsn PC~i% Pector o0 ftoth Radius PVC

0 ?actw 6C 0mUI % Rat d min PCFacto" Smooth 8 Summary of Elbows

0 ftelte 60 3-F P07- TestedFatr 0 sot ethyleneP

Factory - 7- M Our WtWa lter. -I Pecking Do cmawetd -

OFnetor 20j Smoth Namaln PYC

*The test apparatus and methods for determining the impact strength and slip(kinetic coefficient of friction) are presented in Federal SpecificationL-P-378, "Plastic Film (Polyethylene Thin Gage)". Finish 2 film is treate&to allow printing ink to adhere.

GENERAL AMERICAN RIEiUEAPCH DIV1lION

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RESULS AIMf ANALYSIS

Tubing.--The "'rictLon of air in straight polyethylene tubing for lengths fro.m

50 to 450 feet are shown in Figure 5. These curves are based on a least

squares linear logarithmic regression of the test data. The standard error

of estimate; i.e., the mean of the square of the differences between the data

and the fitted curve ranges from 0.007 inches of water gage (iwg) for the

150 foot length to 0.023 iwg for the 40O foot length. Fully inflated 20-inch

diameter plastic tubing has about three-quarters of the pressure drop of

sheet-metal duct. However, the last fifty feet of a plastic duct system

which is not completely inflated has 1-1/2 to 3 times the pressure drop per

foot of fully inflated plastic tubing. The result is that for duct systems

over 100 feet long the pressure drops for sheet-metal and plastic tubing

are approximately the same.

A mathematical expression derived from the least squares fitted curves

of the data is:

P = 1.915 x 10-6 Ql.349 + 0.01096 (L (I)

where:

P = static pressure loss, inches of water gage

q - air flow rate, standard cubic feet per minute (scfm)

L = tubing length (for lengths of 50 feet and longei')

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Faztory Fabricated Elbows.--The elbows with the lowest pressure losses are

factory fabricated smooth radius elbows. The elbows fabricated from four-

mil plastic had lower pressure losses than those fabricated from eight-mil

plastic. The change in pressure loss with centerline radius decreased as the

centerline radius appro- J 6 .0 inches. The elbows with centerline radii of

40-inches and 60-inches have nearly identiLcal pressure losses, indicating

that the trade-off point for centerline radius versus pressure loss is

approximately 40 inches. The mitered elbow had a considerable pressure drop,

and the wire-reinforced elbow developed excessive pressure losses.

The four-mil polyvinyl chloride (PIC) 40-inch smooth radius elbow is the

best factory elbow when considering pressure drop, space requirements, material

and cost. Pigure 6 shows the results of tests performed with this elbow.

The solid lines show the pressure losses fur the elbow with straight lengths

of tubing attached to the downstream side, the broken lines show the pressure

losses for the straight lengths only. It can be seen that the equivalent

length of straight tubing for the 40-inch smooth radius elbow is approximately

50 feet when rully inflated. For the elbow to be fully inflated fifty feet

of straight tubing must be on the downstream side.

OGNEMAL AMaNICAN NSUBARCH CIVISION

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Shelter Fabricated Elbows.--Of the shelter fabricated elbows (see Table I)

the three-piece elbow results in the least pressure loss. The elbow made

from packing boxes produced the largest pressure loss. This elbow was

extremely stable at all flow rates; however, the exit and entrance losses

of the air stream in the plenum-like box produced the high pressure loss.

The best hand-tucked elbow results in pressure drcps considerably higher than

any of the other elbows, and the results were erratic.

Since the three-piece elbcd has the least pressure loss this elbow was

further tested with 100, 200, and 300 feet of tubing (see Figure 7). It can

be seen that the pressure loss of the three-piece elbow with a centerline

radius of 60-inches is equivalent to 90 feet of straight tubing when fully

inflated. For the elbow to be fully inflated fifty feet of straight tubing

must be on the downstream side.

A•plication.--The equivalent duct length of any plastic tubing system can be

determined by adding the total length of straight tubing plus the number of

elbows times their respective equivalent duct lengti: (see Equation 2) -- 50

feet for the factory fabricated elbow and 90 feet for the shefter fabricated

elbow.

FDL L + 50 Nf + 90 14 (2)

where:

,DL Equivalent .uct Lenith of thc system, ftets

L - Lentth -' stralt'ht du,:, 1i T'lhe system, feet

N r number of factory rabri•,nted eL,!ws, ýimensL,ý,ajc.s

N tmi C,S

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- ~ERRATA i-Subject Report: R. B. Neveri). and H. F. BehJ~s, "Friction Loss i

in Flexible Plastic Air Duct", -OC Work Unit

- 1423A, GARD Report 1278-2,. October, 1965.

Pa~ge 26, Fig"'.e 17

IThe ordinate scale of Figure 17 which ranges from 0 to .60 inch

of water gage, static pressure is double the actual value and A

H 'should be changed to indicate a scale range of 0 to .30 inch of

water gage. A

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