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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

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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.

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Fig. 4.1 Schematic diagram of Experimental test-rig

(weighing machine)

102

103

104

105

106

.

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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

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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

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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

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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

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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

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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.

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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

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- 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