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experimental test rig are given in Chapter 4 and the experimental
investigations are presented in Chapter 5.
Chapter 4
EXPERIMENTAL TEST RIGThe test-rig used in the present investigation was well planned,
designed, fabricated and commissioned. A schematic diagram of the
experimental set-up is shown in Fig. 4.1 and an overall photographic
view is shown in Plate 4.1. It consisted of a transparent acrylic jet
100
pump, a centrifugal pump, a clear water tank, a mixing (secondary)
tank and a measuring tank. Its main features are presented in
Appendix-C. All the components of the experimental test rig were
fabricated in the departmental workshops and are described in detail
below:
4.1 MAJOR COMPONENTS OF THE TEST-RIG
There are all together 20 major parts in the experimental set-up
as shown in Fig. 4.1 and also in Plates 4.1to 4.10. Details of each of
them are described below:
4.1.1 Centrifugal Pump (1)* (* refers to part number in Fig 4.1)
A centrifugal pump of two-stage self-priming type capable of
driving primary fluid with a capacity of 280 litres per minute (LPM) with
a head of 45ft. was selected from the market. A photographic view of
the centrifugal pump is presented in Plate 4.2. The pump was an
Engent Engg Co, Kolkata make and was driven by an induction motor
of 5.5 kW (7.5 H.P) capacity running at 1425 rpm. Suction and delivery
ports were of 2" (50 mm) size. The pump Head vs. Discharge
characteristics are presented in Fig. B.4 in Appendix-B.
101
Fig. 4.1 Schematic diagram of Experimental test-rig
(weighing machine)
102
103
104
105
106
.
107
4.1.2 Jet Pump (7)The body of the jet pump was
made from an acrylic (perspex) solid
rod of 3" (76.2 mm) diameter. The
detailed schematic diagram of the jet
pump is shown in Fig. 4.2. The suction
nozzle, the throat (mixing chamber),
and the diffuser portions were made by
drilling and boring the solid rod. It was
fixed at the centre of the bottom cone
of the mixing chamber, on its four legs.
Holes of 1/8"(3 mm approx.) were
tapped in these legs, and these served
as locating pins and also for fixing the
jet pump. Pressure taps were provided
at three points on the jet pump body,
i.e. one at throat entrance, the second
at throat exit, and the third one at
diffuser exit. At the end of the diffuser
internal threads were made to fit a
1"(25.4 mm) transport pipe. The jet
pump assembly was fabricated in the
workshop, erected and commissioned
in Hyd. Machines lab, Mech. Engg.
Dept. at IIT Kharagpur, where the
108
experimental investigations were carried out.
4.1.3 Clear Water Tank (15)A rectangular tank of size 1.8m long, 0.9m wide, and a depth of
0.9 m having a capacity of approximately 1500 litres was used for
storage of clear water. The suction line of the centrifugal pump was
provided at a level of 50 mm above the bottom of the tank. This
prevented any sand particles and stray solids from entering the
centrifugal pump impeller and rotameters. This tank was provided with
an overflow pipe of 100 mm nominal diameter with a long radius bend
(14). The overflow was directed into the mixing (secondary) tank.
4.1.4 Mixing tank / Slurry tank (9)This is also referred to as the secondary tank or slurry tank
(Plate 4.3). It was a square duct of 230mm x 230mm with a height of
1.8 metres. It was fabricated with transparent acrylic sheets of 10 mm
thickness. The bottom portion of the tank was made conical and
detachable. It was made in such a way that it formed a smooth
transition from square on top to circular at bottom. This allowed a
smooth passage of solids without any deposits at the sides or corners of
the slurry tank thus avoiding dead zones. The upper portion of the
detachable bottom was square matching the size of the slurry tank
(230 x 230 mm). The detachable bottom was provided with a flange for
fastening it to the bottom of the mixing tank by bolts and nuts. A
stuffing box type arrangement was made in the bottom sheet of the
cone to prevent leakage of water from the bottom. A screw jack type
arrangement was made for moving the nozzle and for correct
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positioning with respect to the throat entrance of jet pump. The details
of arrangement are shown in Fig. 4.3.
Fig. 4.3 Nozzle adjusting arrangement
4.1.5 Measuring Tank (11)
The measuring tank (Plate 4.5) was made to facilitate the
measurement of both volume flow rate and weight flow rate of the
discharge from the transport pipe. It was a cylindrical tank of diameter
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280 mm and height 400 mm, with a conical bottom. An "L" shaped 2"
(50 mm) diameter drain pipe with a gate valve was fitted to the bottom,
for draining the sample collected for the measurement purpose. The
exit of this measuring tank was kept into the sieve bend (13) so that,
the sand is re-circulated after measurement. The measuring tank was
fitted with a vernier depth gauge for taking the measurements. An
acrylic sheet with holes drilled on it was arranged vertically across the
tank as a baffle board at the centre of the tank to dampen the
fluctuations of the water or slurry sample collected in it. The measuring
tank was fitted on a platform scale to record the weight of the sample
collected. This arrangement facilitated the measurement of both the
volume flow rate and weight flow rate of the discharge through the
transport pipe.
4.1.6 Rotameters (3)
Two Rotameters one of capacity 5 to 50 Litres per minute (LPM)
and another of capacity 10 to 100 LPM were installed in the primary
line (drive line) to measure the primary flow rate (Plate 4.10). Gate
valves V3 and V4 were fitted in the delivery line of the centrifugal pump
to isolate any one of the rotameters depending upon the quantity of
flow rate required. The idea of having two rotameters when possibly one
could do the job was to maintain the same level of accuracy when flow
rate was small. The rotameters were calibrated using the measuring
tank and the results are presented in Fig. B.2 and Fig. B.3 in
Appendix-B.
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4.1.7 Manometer Bank (19)
A manometer bank (Plate 4.9) placed at a convenient height (for
easy observation) was used to record the pressures at various
important points on the jet pump and on the transport pipe. This basic
and simple instrument was used in place of more sophisticated
transducers because of its reliability. Manometers M3, M4 and M5 were
connected to pressure taps at throat entrance, throat exit and diffuser
exit respectively. Manometers M6, M7, M8 and M9 were connected to
pressure taps on the transport pipe as shown in Fig. 4.1. A pressure
tap on primary nozzle assembly was connected to manometer M2.
4.1.8 Pressure Transducers (20)
Pressure transducers (Plate 4.9) were connected in parallel to the
manometer bank. They were supplied by Syscon Instruments Pvt. Ltd.,
Bangalore (India). Since the pressures at the throat entrance and throat
exit are expected to be very low, a vacuum pressure cell was connected
parallel to the manometer M3 (at throat entrance); and another vacuum
pressure cell was connected parallel to manometer M4 (at throat exit). A
pressure transducer of 0 to 2 Kgf/sq. cm range was connected parallel
to manometer M5 (at diffuser exit). All the remaining four pressure taps
M6, M7, M8 and M9 on the transport pipe were connected to a 0 - 1
Kgf/sq. cm pressure transducer through a switching arrangement as
shown in Plate 4.9. The pressure tap on the primary nozzle assembly
was connected to a 0 to 5 Kgf/sq. cm pressure transducer parallel to
manometer M2. All the pressure transducers were calibrated using a
dead weight pressure gauge tester.
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4.1.9 Primary Nozzles (6)
Three brass nozzles (Plate 4.8) of 6 mm, 7 mm and 8 mm inner
diameter were fabricated in the workshop of Mech Engg Dept and were
used in the experiment. These could be interchanged easily. The
different nozzle diameters were chosen to get three different area ratios,
R = 0.223, 0.304 and 0.397 respectively. Nozzles were brazed to the
ends of three short pipes respectively. This pipe and another short pipe
of 250 mm long and 25 mm inner diameter were fitted to form a Tee
joint. The lower open end of the Tee joint was sealed. All the joints were
made leak proof. Three independent sub-assemblies were made for the
three nozzles as shown in plate 4.8.
4.1.10 Nozzle Adjusting Device
The details of this arrangement are shown in Fig. 4.2 and also in
Plate 4.8. The arrangement used was basically like a screw-jack
mechanism. Three mild steel rods of 15 mm diameter and 300 mm long
were threaded on both ends (studs/pillars). One end of each rod was
fitted into the end plate of the conical bottom of the mixing tank. Two of
these rods were fitted with a 33 mm gap in between to allow the hori-
zontal pipe of primary nozzle assembly to slide in between these two
rods. The primary nozzle was inserted into the suction nozzle of the jet
pump. A stuffing box arrangement (gland packing) was used to prevent
leakage from the bottom of the slurry tank. The lower end of Tee was
fitted to the square threaded screw with a bolt and nut. The square
threaded nut, which engaged with the screw, was fitted into a bridge
plate. The axial movement of the nut was prevented by a flange on one
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side and by the hand-wheel on the other side of this bridge. The hand
wheel was used to rotate the nut, which in turn pushes up or pulls
down the nozzle assembly depending upon the direction of rotation of
the hand wheel. The arrangement was similar to a steam stop valve in
the upside down position.
4.1.11 Distance Pieces (Spacer Blocks)
Distance pieces were used to set the distance (s) between the tip
of the nozzle and throat entrance of jet pump in such a way that, the
non-dimensional quantity of (s/dt) is in steps of 0.5, 1.0, 1.5, and 2.0.
The distance pieces were made from a 25 mm thick acrylic sheet and
are as shown in plate 4.8. Initially the primary nozzle tip was aligned
with the throat entrance of jet pump i.e. the distance s = 0, and the
corresponding distance between the Tee of primary nozzle and the
bottom plate of the slurry tank was measured. It was found to be 96
mm. A piece of this length was used to set the distance s = 0, giving an
s/dt = 0.0. This was done by an indirect method. The distance of the
throat entrance from the bottom of the plate was measured and that
was subtracted from 205 mm, which is the distance between the tip of
the nozzle to the horizontal pipe. Thus when s = 0 (or s/dt = 0), the tip
of the nozzle coincided with the throat entrance of jet pump. For
measuring this, a distance piece of 96 mm long was needed. Later 6.35
mm, 12.7 mm, 19.05 mm, and 25.4 mm thick distance pieces were
made and used to obtain the various (s/dt) ratios of 0.5, 1.0, 1.5, and
2.0 respectively. The distance pieces were prepared by grinding and
114
were checked using metrology instrumentation. The nozzle was moved
in steps of these distances using the spacer blocks.
4.1.12 Sieve-Bend (13)
The sieve-bend (Plate 4.6) was made of sheet metal. The purpose
of this part was to separate the solids from the transported slurry. A
wire mesh of 125-micron opening was fixed in the channel passage.
The sieve-bend is placed over the clear water tank in an inclined
position as shown in Fig. 4.1. Part of the water passed through the wire
mesh into the clear water tank, while remaining part of water carried
the sand along with it into the mixing (slurry) tank. Thus the slurry got
re-circulated into the mixing tank.
4.1.13 Long Bend / Overflow Bend (14)
A long bent pipe of 100mm diameter was arranged with swivel
action. It was used to allow the overflow of the clear water tank into the
slurry tank for equilibrium steady state condition. By lifting the swivel
bend (14) the overflow into the slurry tank can be prevented. It was
lifted up while emptying the slurry tank.
4.1.14 Solids-Trap and Air-Trap Chambers
These were used for preventing solid particles or air bubbles from
entering the manometer connections. Solids trap was made by cutting
50 mm long tubes from a 50 mm diameter acrylic pipe. The ends were
closed with 3 mm thick acrylic sheet. Chloroform mixed with a small
quantity of acrylic powder was made into a solution and was used for
joining the acrylic pieces. A thin layer of araldite was applied to prevent
115
any possible leakages. The pressure tap inlet and outlets were
connected to these chambers on the same side. These trap chambers
were arranged very close to the point of pressure tap. Stray solid
particles if any that entered the pressure tap got trapped in the
chamber and thus prevented the blockage of the line connecting the
manometer bank and pressure transducers.
4.2 OVERALL ASSEMBLY OF THE EXPERIMENTAL SET-UP
The overall assembly of the experimental set-up was as shown in
Fig. 4.1 and Plate 4.4. The suction port of the centrifugal pump was
connected to the clear water tank. The delivery line of the centrifugal
pump was reduced from (2") 50.8 mm to (1") 25.4 mm. A by-pass line of
(1") 25.4 mm size was also connected to the delivery line of the
centrifugal pump (Plate 4.2). A gate valve V5 was fitted in the by-pass
line to control the flow in the primary path whenever necessary.
Rotameters (3) were fitted in the primary path after the gate valve V2.
The common delivery of the rotameters was connected to the primary
nozzle through a hose-pipe of about 500 mm long. Hose-pipe was used
to allow the movement of the primary nozzle up and down. The jet
pump was fitted at the bottom cone of the mixing (slurry) tank. An
acrylic (acrylic) pipe of 25.4 mm internal diameter was used for
transport of slurry. The transport pipe was fitted into the diffuser of jet
pump. Pressure taps were connected to the manometers with 3 mm
internal diameter polyethylene tubing. Two elbows and two short pipes
were used to make the flow diverter. The short end pipe along with the
116
elbow (10) was rotated to divert the flow into the measuring tank (Plate
4.5) whenever the flow measurement was required. The return line
from the flow diverter consisted of a funnel made with sheet metal and
a 50 mm diameter acrylic pipe (12). The lower end of the funnel stem
was directed on to the sieve-bend (13). The sieve-bend was arranged
over the clear water tank with suitable inclination towards the mixing
tank. When the slurry (sand and water mixture) from the delivery of the
transport pipe falls on the sieve, a part of the water passes through the
wire mesh and falls into the clear water tank, while the sand and other
part of the water falls into the mixing tank. The inclination of the sieve-
bend was decided by trial and error so that the entire sand is washed
away into the slurry tank. An overflow pipe was arranged for the clear
water tank (14). A 100 mm inner diameter long radius bent pipe (14)
was fitted towards the top edge of clear water tank (15) to allow the
excess water into the mixing tank. A pit of 2m long one metre wide and
3m deep was made for housing the mixing (secondary) tank along with
the jet pump assembly. A platform was arranged at a height of 0.75 m
from the bottom of the pit, for changing nozzle and also for adjusting
the nozzle position with respect to the throat entrance. A stuffing box
arrangement (gland packing) was made around the nozzle entry into
the mixing tank for preventing leakage from the bottom of the mixing
tank.
4.3 WATER / SLURRY FLOW PATHS
The experimental set-up was made into a closed loop system
consisting of three-flow paths - the primary, secondary and the tertiary
117
paths. These paths are marked in different colours as shown in Fig. 4.4
for easier identification of the three paths.
4.3.1 Primary Path
The primary path starts from the clear water tank to the
primary nozzle of the jet pump. It consisted of the centrifugal pump,
rotameters, the hose-pipe, and the primary nozzle assembly. The
centrifugal pump received clear water from the water tank and
supplied it to the primary nozzle through a 1” nominal diameter G.I.
pipe. The primary path is shown green in colour in Fig. 4.4 below.
118
Fig. 4.4 The three flow paths- primary, secondary and the tertiary
4.3.2 Secondary Path
The secondary path starts from the slurry tank to the mixing
chamber (throat) of the jet pump. It consists of the slurry tank and the
annular duct of the suction nozzle of the jet pump. The secondary flow
119
- water or slurry (water and sand mixture) - moves down the slurry
tank and enters the suction nozzle of the jet pump before mixing with
the primary jet coming from the primary nozzle. The secondary path is
shown in brown in Fig. 4.4.
4.3.3 Tertiary Path
The tertiary path begins from the mixing region of primary and
secondary fluids in the jet pump and ends at the delivery end of the
transport pipe. The tertiary path consists of the throat, diffuser, and
the transport pipe with the flow diverter. The tertiary path starts from
the annular suction nozzle of the jet pump for (s/dt) ratio greater than
zero. When s/dt = 0.0, the tertiary path begins from the throat entrance
itself. The tertiary path is shown red in colour in Fig. 4.4.
The experimental set-up as described in this chapter is fabricated
and commissioned to carry out the experimental investigations. A
detailed experimental procedure is presented in Chapter 5.
Chapter 5
EXPERIMENTAL PROCEDURE ANDDATA REDUCTION
A detailed procedure of experimentation carried out by the
researcher, determination of local properties and terminal velocity of sand