Tor Fluid Hydraulics

EXPERIMENTAL METHODS

IN

FLUID MECHANICS

AND HYDRAULIC

Engr. Zukbee N. ATor Festus L.

JOMAT Production

Copyright © 2013 Zukbee N. A. & Tor Festus L.

Revised edition

Published byHARRISCO PRESSPort Harcourt Nigeria

ISBN: 989 40986 8 13

ALL RIGHT RESERVED This manuscript may not be reproduced in part or in full or stored in a retrieval system or transmitted in any form or in any means, electronic, mechanical, photocopying, recording or otherwise except for brief quotation in critical articles or review-without the prior written consent of the copyright owner and the publisher. This book is sold subject to the condition that it should not by way of trade or otherwise be lent, hired out or otherwise circulated without the copyright owner consent, in any form of binding or cover that in which it is published and this condition being imposed on the subsequent purchaser.

Designed and Printed: JOMAT Services,

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Email: [email protected]

ii

To

Our wives

Mrs. Sira Zukbee&

Mrs. Kornebari Evelyn Tor

iii

PREFACE

The book Experimental Method in Fluid Mechanics and Hydraulics has been carefully arranged to cover the NBTE practical requirement for students offering Fluid Mechanics and some related hydraulic course in engineering departments, especially Mechanical and Civil Engineering. It also covers the University scheme for practical on the basic fluid mechanics.

There is also an experiment on turbine and pumps to help the student understand the principles behind the operation of pumps and turbines when they are expose to in the industries.

Students who successfully carried out most of the experiment in this book will find Fluid Mechanics very interesting.

iv

Acknowledgement

The Authors wish to acknowledge their friends and colleagues in the Polytechnic for the kind assistance and contribution especially the Head of Department, Engr J. N. Beredam for allowing them use the school facilities to perform most of the practical outline in this book.

Zukbee N. A. & Tor Festus L.

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CONTENTS

PREFACE ivACKNOWLEDGEMENT VCHAPTER ONE 1

BASIC HYDRAULIC BENCH 1EXPERIMENT 1.1 5THE STABILITY OF A FLOATING BODY 5

CHAPTER TWO 8EXPERIMENT 2.1 8THE POSITION OF HYDROSTATIC PRESSURE 8

CHAPTER THREE 12EXPERIMENT 3.1 12DISCHARGE THROUGH AN ORIFICE 12EXPERIMENT 3.2 15TO DETERMINE THE COEFFICIENT OF DISCHARGE 15

CHAPTER FOUR 17EXPERIMENT 4.1 17BERNOULLI’S THEOREM DEMONSTRATION EXPERIMENT 17

CHAPTER FIVE 20EXPERIMENT 5.1 20DISCHARGE OVER WEIR (Rectangular Notch) 20EXPERIMENT 5.2 23DISCHARGE OVER WEIR (V- Notch) 23

CHAPTER SIX 26EXPERIMENT 6.1 26FRICTION LOSS ALONG A PIPE 26

CHAPTER SEVEN 30EXPERIMENT 7.1 30FLOW CONDITION 30EXPERIMENT 7.2 33OSBORNE REYNOLD’S EXPERIMENT 33

CHAPTER EIGHT 35EXPERIMENT 8.1 35OPEN CHANNEL FLOW VISUALIZATION 35EXPERIMENT 8.2 38VISUALIZATION OF FLOW OVER OR AROUND IMMERSED OBJECT 38

CHAPTER NINE 41EXPERIMENT 9.1 41IMPACT OF JETS 41

CHAPTER TEN 45EXPERIMENT 10.1 45PRESSURE GAUGE CALIBRATION 45

CHAPTER ELEVEN 48EXPERIMENT 11.1 48LOSSES IN PIPE BENDS 48

CHAPTER TWELVE 52EXPERIMENT 12.1 52STEADY UNIFORM FLOW 52

CHAPTER THIRTEEN 54

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EXPERIMENT 13.1 54THE CHANGE IN DEPTH AT A HYDRAULIC JUMP 54EXPERIMENT 13.2 56FLOW UNDER A SLUICE GATE WITH A HYDRAULIC JUMP 56

CHAPTER FOURTEEN 58EXPERIMENT 14.1 58FLOW OVER A BROAD - CRESTED WEIR 58

CHAPTER FIFTEEN 60EXPERIMENT 15.1 60FLOW THROUGH A VENTURE FLUME 60

CHAPTER SIXTEEN 63EXPERIMENT 16.1 63PERFORMANCE CHARACTERISTICS OF A SINGLE PUMP AT A SINGLE SPEED

63EXPERIMENT 16.2 65PERFORMANCE CHARACTERISTICS OF SIMILAR PUMP IN PARALLEL 65EXPERIMENT 16.3 67PERFORMANCE CHARACTERISTICS OF TWO SIMILAR PUMP IN SERIES 67

CHAPTER SEVENTEEN 69EXPERIMENT 17.1 69PERFORMANCE CHARACTERISTICS OF A PUMP 69

CHAPTER EIGHTEEN 72EXPERIMENT 18.1 72PRESSURE HEAD AND FLOW RATE AT VARIOUS SPEED OF A RECIPROCATING PUMP 72EXPERIMENT 18.2 76RELATIONSHIP BETWEEN PRESSURE HEAD, FLOW RATE, TORQUE, AND POWER OF A RECIPROCATING PUMP 76

CHAPTER NINETEEN 79EXPERIMENT 19.1 79PERFORMANCE CHARACTERISTICS OF PELTON IMPULSE TURBINE 79

REFERENCE 83

vii

Hydraulic Bench/ Floating Body Stability

CHAPTER ONE

BASIC HYDRAULIC BENCH

The hydraulic bench as shown in a line diagram of fig. 1.1 and a three dimensional diagram of fig. 1.2, is intended to provide facilities for performing a number of simple experiments in hydraulics. In fig. 1.1 below is the arraignment of a single unit in which a small centrifugal pump P draws water from a sump S resting below the bench, and delivers it to a bench supply valve V. The delivery pressure at this value is recorded on a Bourdon pressure gauge G, which is provided with a connection A for calibrating the gauge with a dead weight tester.

G

V

A

P

O B

S

D W

F

Fig. 1.1 Line diagram of a hydraulic bench.

Below the bench is a weighing tank W into which the discharge from apparatus being tested on the bench may be directed through a short pipe D terminating at flange F just above the bench level.

1


1. S igh t tu be sca le2 . F low con tro l va lve3 . M otor s ta rt/s top4 . D u m p v a lv e h an d le5 . D ra in va lve6 . S u m p tan k cap . 16 0 lts .7 . M e asu rin g cy lin der8 . Tran sparen t p ipe9 . P u m p & m otor10 . S ide c han n els11 . Q u ick re lease c on ne cto r (w ith

flex ib le su pp ly p ipe)12 . In le t stillin g ba ffle s lo ts

13 . O pen ch ann el14 . W eir carr ier15 . Ta n k s tillin g ba ffle16 . Vo l. M ea su rin g tank17 . D u m p v a lv e18 . O ver f low8

7

Fig. 1.2 A Three dimensional diagram of a Hydraulic Bench

The weighting tank W is supported at one end of a weigh beam, the other end of which carries a weight hanger sufficient to balance approximately the dry weight of the tank. The outlet valve B in the base of the tank may be operated through a

2


mechanism by an external handle. An over flow pipe O is also provided.Apparatus under test is placed on the bench and connected by flexible pipe to a bench supply valve which normally serves to regulate the rate of flow through the apparatus. Another flexible pipe is lead from the exit of the apparatus to the flange above a weighing tank: so that the discharge from the exit of the apparatus is returned through the open valve at the base of the tank to the sump. The Hydraulic Bench comprises the following;

1. Volumetric measuring tank2. Sump tank, 3. Centrifugal pump, 4. control valve, 5. stilling baffle, 6. slight tube with level scale and 7. a dump valve.

It is also incorporated with it an earth leakage circuit breaker.

Experiments are not carried out on the hydraulic bench alone but it is used in conjunction with the following apparatus:-1. A Dead Weight Pressure gauge calibrators.2. Metacentric Height Apparatus 3. Bernoulli’s Theorem Demonstration Apparatus 4. Basic Weirs5. Orifice and Jet Apparatus 6. Impact of Jet Apparatus7. Osborne Reynolds’s Apparatus8. Pipe Friction Apparatus9. Flow visualisation channel 10. Losses in Bends Apparatus11. Flow Demonstration Apparatus12. Hydrostatic Pressure Apparatus

3


A measuring cylinder 7 is provided with the hydraulics bench for

measurement of very small flow rates.

Attention is drawn to the following points which should be

observed for safe and satisfactory operation of the bench.

1. Before starting the pump ensure that the sump is full and

that the bench supply valves are turned off.

2. If a leak develops so that water drips on to the electric

motor or starter, stop the pump immediately and isolate it

from the electrical supply by withdrawing the plug which

supplies it. The connection should not be made until the

leak has been sealed. A small amount of water leaking on to

the bench top, however, is of small concern, as it drains

back into the sump.

3. When making connections by flexible hose it is usually

sufficient to rely on friction between the metal pipe and

the hose to maintain the water tightness of the

connection. Where however the connection is subjected to

the full pressure delivered to the bench supply valve, or if

the hose is a loose fit on the metal pipe, it is advisable to

secure the connection with a hose clip tightened by a

screw driver or a key made for the purpose.

4. At all times other than when a discharge measurement is

being made, the dump valve in the base of the measuring

tanks should be kept open. Although each tank has an

overflow pipe. But this is inadequate to deal with the

maximum discharge.

4


EXPERIMENT 1.1

THE STABILITY OF A FLOATING BODY

AIMTo demonstrate the stability of a body floating in a fluid.

APPARATUS 1. Hydraulics Bench 2. Metre Rule 3. Weighing Machine4. Metacentric Height Apparatus

T H E O R Y:M

Fig. 1.3 Metacentric height Apparatus

5


THEORY

If a jockey weight m is moved a horizontal distance x from its position and if the total weight of the floating assembly is W; then the corresponding movement of the centre of gravity G of the whole assembly in the direction parallel to the base of the

floating body is . If this movement produces a new

equilibrium position at angle , then the metacentric height is

given by GM = , where M is the metacentric.

If B is the centre of buoyancy, the distance BM may also be

calculated from . Where I = 2nd moment of area about an

axis through the centriod of the area of the body at the plane of the water surface, the axis being perpendicular to the plane in which angular displacement take place.

V = volume of liquid displaced.

For a rectangular pontoon B lies at a depth below the water surface

equal to the total depth of immersion, and .

GM = BM – BG

PROCEDURE

First weigh the various components of the floating assembly and

measure the length and width of the pontoon. Determine the

centre of gravity of the pontoon by turning it on its side and

supporting it at the stem on the edge of a steel rule to obtain the

point at which it balances. To obtain a convenient point of

balance, it may be necessary to move the adjustable weight along

the stem to a suitable position. Mark the point of balance –

Centre of Gravity. Float the pontoon in the volumetric tank

water. Record angles for various positions of the jockey weight

6


on both sides of the centre O with an increment of 10mm. Set

the adjustable weight at another different height for a new

position of centre of gravity and repeat the procedure.

PRESENTATION OF RESULTS AND CALCULATIONS

Dimensions of Pontoon Length = …………., Width = …………., Jockey weight = …… Weight of assembled pontoon = ……….Position centre of gravity CG from base of pontoon.Y = …………., Depth of immersion, d = ………….

Position of centre of Buoyancy CB = ………….

x Right x Left

Plot GM against and read GM when = 0

x is distance of moveable mass is angle of heel GM is metacentric height

Check by calculation BM =

GM = BM – BG =

QUESTIONS 1. Does the position of the metacentric depend on the position of

the centre of gravity?

2. Does the metacentric height vary with angle of heel?

7

Hydrostatic Pressure

CHAPTER TWO

EXPERIMENT 2.1

THE POSITION OF HYDROSTATIC PRESSURE

AIMTo determine the position of the centre of pressure of an immersed plane surface and to compare it with the theoretical position.

APPARATUS1. Hydrostatic pressure apparatus 2. Hydraulic bench

THEORY The force (F) acting on a submerged surface is F = P.A - g XA.This is the algebraic sum of all the small forces acting on their respective position and it act through a point called centre of pressure. Taking moment about O, and note that force on trip = xgAMoment of force on strip = x2gABut x2A =Io (2nd moment of area about “O”)

And moment = FZ FZ = gIo

Since F = A for resultant force

Then

From parallel axis theorem

8


Fig. 2.1 Hydrostatic Pressure Apparatus

9


This equation is applied also for partially submerged plated except that the Area of plate varies

Z =

That is, centre of pressure is down the section of plate that is

submerged.

PROCEDURE

From the end of the balance arm hang the balance pan and

position the balance arm on the knife edge pivot. From the drain

cock, connect a hose sump and also connect hose from the bench

feed to the triangular aperture on the top of the Perspex tank.

With the help of the adjustable feet and spirit level, level the

tank. Move the connecter balance mass until the balance arm is

horizontal with the drain cock close, admit water to the

apparatus until the level reaches the bottom edge of the

quadrant. Place a mass on the balance pan: slowly add water

into the tank until the balance arm is horizontal. Record the

water level on the plate and the mass on the balance pan.

Repeat the above procedure for each increment of mass until the

water level reaches the maximum reading on the scale. Remove

also each increment of mass noting masses and water level until

all the masses have been removed.

10


PRESENTATION OF RESULT AND CALCULATION

No. Mass m(g) mm xCA xCT (mm)12345

A = actual

T = TheoreticalmgP = FxCA

Plot xc actual against xc theoretical for the partially and fully

submerged cases.

CONCLUSION

1. Why is the centre of pressure always below the centriod?

2. Explain the reason for any discrepancies between the actual and

the theoretical results.

11

Discharge Through an Orifice

CHAPTER THREE

12


EXPERIMENT 3.1

DISCHARGE THROUGH AN ORIFICE

AIMTo determine the coefficient of velocity for a small orifice

APPARATUS 1. Hydraulic Bench

2. Orifice and Jet Apparatus

3. Stop Watch.

THEORY

Note: The plan of vena contractor is taken as the datum for measuring X.

PROCEDURE Adjust the feet to level the apparatus and ensure that the part of

the Jet coincides with the row of measuring needles.

Connect the apparatus to the bench delivering valve and the

overflow pipe hose to the sump tank. After placing a sheet of

paper on the backboard raise the needles to clear the path of the

water jet and also raise the overflow pipe.

13


Open the flow control valve, to admit water into the head tank.

Adjust the valve until the water is just spilling into the overflow.

Record the head h on the scale. Assess the position of the vena

Fig

. 3.1

Ori

fice

an

d je

t app

arat

us

14


contractor visually and note the distance from the orifice. Adjust

each of the needles in turn to determine the jet path, making the

position of the top of the needles on the sheet of paper using the

other orifice plate.

Repeat for various values of h by moving the overflow. Repeat

using another orifice plate.


Orifice A Orifice BHead

h(mm)

Height

Y(mm)

Distance

X(mm)

X2(mm2) Head

h(mm

)

Height

Y(mm)

Distance

X(mm)

X2(mm2)

Plot against y.

Find CV from the slope of the graph.

15


EXPERIMENT 3.2

TO DETERMINE THE COEFFICIENT OF DISCHARGE

AIMTo find experimentally the coefficient of discharge for a small

orifice for flows under constant and varying head.

APPARATUS 1. Hydraulics Bench

2. Orifice and Jet Apparatus

3. Stop Watch.

See Fig. 3.1above

THEORY

PROCEDURE Measure the orifice diameter, removing the orifice plate if necessary, measure the internal dimensions of the header tank. Connect the apparatus to the bench, levelling by adjusting feet, ensuring the overflow pipe runs into the sump tank. Raise overflow pipe to a suitable level, release water into the tank. Control the flow until the water is just spilling into overflow. Record the head h on the scale, measure the flow rate using the volumetric tank, or by intercepting the jet with a measuring cylinder. Repeat for different water levels. For flow under varying head, the overflow pipe is raised to obtain maximum head, the header tank filled to overflow level and the inlet water feed closed. Start a stop watch when the level reaches the first convenient scale mark (noted as h). Take a reading of the head (h2) at 20 second intervals.

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The above should be repeated using the other orifice.

PRESENTATION OF RESULTS AND CALCULATIONS:

Constant Head Variable HeadHead h(mm) Volume

water(l)

TimeT

(sec)

Q Q2 Head h(mm)

Height(mm)

TimeT

(sec)

(a) Plot Q2 against h and obtain Cd from the slope of the graph

for constant head.

(b) Plot T against and obtain Cd from the slope of the graph

for variable.

Determine RO Reynolds number at each head and plot Cd versus

RO.

17

Discharge over Weirs

CHAPTER FOUR

EXPERIMENT 4.1

BERNOULLI’S THEOREM DEMONSTRATION

EXPERIMENT

AIM To investigate the validity of Bernoulli’s theorem as applied to

the flow of water in a tapering duct.

APPARATUS 1. Bernoulli’s theorem demonstration apparatus (Venturi

meter) 2. Hydraulic bench3. Stop watch

Fig. 4.1 Bernoulli’s theorem apparatus THEORY

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If an incompressible fluid is to flow through a venture meter and if the cross-sectional area at any section (1) upstream is denoted as a1, and at the throat section (2) as a2 and at any other section n as qn1, then piezometer tubes at these sections will register ht, h2 and hi. Assuming that there is no loss of energy, Bernoulli’s theorem

states that

From the continuity equation Q = a1 V1 = a2 V2 = an, Vn

Substituting this in Bernoulli equation for V1 will give

In practice there is some loss of energy between section (1) and (2) and it is customary to allow for such discrepancy by writing.

Where Cd is known as the coefficient of the meter.

PROCEDURE First open the control valve downstream of the meter and the bench supply valve so as to allow water to run for a few seconds to clear air pockets from the supply system. Then gradually close the control valve. When the water levels have risen to a convenient height, gradually close the bench valve, so that, as both valves are finally shut off the meter is left containing static water under moderate pressure. Set the adjusting screws at the base, so that the piezometers each read the same value. Take the

19


reading of the maximum available (h1 – h2) i.e. with h1 close to the top of the scale and h2 close to the bottom.(This condition is achieved by gradually opening both the bench valve and the control valve. Successive openings of either valve will increase the flow and the difference between h1 and h2. If difficulty is experienced in reaching the desired condition air may be released from or admitted to the manifold through the small air valve at its end).Measure the quantity of water flowing by collecting it in the weighing tank, record the time taken to collect this amount and while this is in progress read values of h1 and h2 from the scale. At reducing values of (h1 – h2), take a series of readings

PRESENTATION OF RESULTS AND CALCULATION

Tube No.

Dia. of cross section (mm)

Area of cross section (mm2)

Mamometer levels (h)mm

Flow Rate Q

Probe Distance (mm)

Probe Manometer level (mm)

Fluid Velocity (m/s)

1.2.3.4.5.6.

Choose any two value of h and plot a graph of Q vs (h1 – h2)1/2

Calculate the coefficient of the meter.

20

Discharge Over Weirs

CHAPTER FIVE

EXPERIMENT 5.1

DISCHARGE OVER WEIR (Rectangular Notch)

AIM To study the characteristics of flow over a rectangular notch.

APPARATUS1. Hydraulic bench

2. Rectangular notch

3. Hook and pointer gauge

4. Stop watch

THEORY The total flow rate Q through a rectangular weir is given by:

Where b = width of rectangular weir

H = head on weir

Taking into account losses and contraction of the jet, Q for a

rectangular notch can be given as

Where Cd is the coefficient of discharge.

Also it can be said that

Q = KHn or Log Q = Log K + nLog H

21


If experimental results are plotted having Log H as abscissa and

Log Q as ordinate, then the slope of the straight line = n, and the

intercept on the axis of Log Q = Log K.

(R ectan gu lar)F

ig. 5

.1 R

ecta

ngu

lar

not

ch a

ppar

atu

s

22


PROCEDURE First level the apparatus. Admit water from the bench supply to

the apparatus until the level is approximately correct and bale

out or in using a small beaker until the crest of the weir lies just

in the surface. Place a steel rule on the crest. Then set the hook

gauge on the water surface in the still tube and take the zero

reading. From the bench supply valve, regulate the flow. First

start with a maximum discharge and subsequent readings with

roughly equal decrement in head. Measure the discharge and

head on the weir at each stage. About six different discharges for

each notch should be made.


Record breadth of notch1. Tabulate volumes, time and heads2. Compute and tabulate Q, , Cd, , Log Q, Log H

Plot against H Log Q ,, Log H

Cd ,, H

Note:

CONCLUSION

1. Is Cd constant?

2. Estimate an average valve of Q for the test

3. Can the empirical formula Q = KHn use in describing the

relationship between Q and H? If yes find the value of K and n.

4. If Cd is not constant suggest a functional relationship

between Cd and .

23


EXPERIMENT 5.2

DISCHARGE OVER WEIR (V- Notch)

AIM To study the characteristics of flow over a V-notch.

APPARATUS1. Hydraulic bench

2. V-Shaped notch

3. Hook and pointer gauge

4. Stop watch

THEORY The total flow rate Q through a V-notch of angle 2, is given by

Where H = head on weir

Taking into account losses and contraction of the jet, Q for V

notch can be given as

Where Cd is the coefficient of discharge. Also it can be said that

Q = KHn or Log Q = Log K + nLogH

If experimental results are plotted having Log H as abscissa

and Log Q as ordinate, then the slope of the straight line = n, and

the intercept on the axis of Log Q = Log K.

24


PROCEDURE First level the apparatus. Admit water from the bench supply to

the apparatus until the level is approximately correct and bale

out or in using a small beaker until the crest of the weir lies just

in the surface. The reflection of the V in the surface serves to

(V-no tc h )F

ig. 5

.2 V

-not

ch a

ppar

atus

25


indicate whether the level is correct or not. Then set the hook

gauge on the water surface in the still tube and take the zero

reading. From the bench supply valve, regulate the flow. First

start with a maximum discharge and subsequent readings with

roughly equal decrement in head. Measure the discharge and

head on the weir at each stage. About six different discharge for

each notch should be made.

PRESENTATION OF RESULTS AND CALCULATION FOR V- NOTCH

1. Record breadth of notch.2. Tabulate volumes, time and heads

3. Compute and tabulate Q and

4. Plot against H and find Cd from the slope of the graph.

QUESTION1. Is Cd constant throughout experiment?2. What are the advantage and disadvantage of plotting

against H instead of Q against .

26

Flow Profile

CHAPTER SIX

EXPERIMENT 6.1

FRICTION LOSS ALONG A PIPE

AIMTo investigate the variation of friction head along a circular pipe

with the mead flow velocity in the pipe.

APPARATUS 1. Hydraulic bench

2. Pipe friction apparatus

3. Measuring cylinder

4. Thermometer

5. Stop watch

THEORY The frictional resistance to which a fluid is subjected as it flows

along a pipe results in a continuous loss of energy or total head

of the fluid. Osborne Reynold recorded a number of experiments

to determine the laws of resistance in pipes. The parameters

which determine whether flow is laminar or turbulent in any

particular case are given by Reynold as

Where Re = Reynold’s number = Density of fluidV = Velocity of flowD = Diameter of pipe = Coefficient of Viscosity of the fluid

27

Flow Profile

Re has a practical maximum value of 2000 laminar flow. For pipe flow calculations, the Darcy-Weisbach equation

is generally adopted, when

Fig

6.1

Pip

e F

rict

ion

app

arat

us

28

Flow Profile

hf = Head loss or drop in hydraulic grade line

L = Length of pipe

f = Friction factor

Loss of head for laminar flow can also be expressed by the

pioseusuille’s equation


Volume (liters)

Time(s)

Water man. Reading (mm)

Mercury man. reading (mm)

Area of test section =

of test section =

Length of test section =

Water temperature =

Compute and tabulate the value of friction head hf, as head of system

fluid (water).

From the experiment obtain the value of volume, time and cross

sectional area of test section, calculate and tabulate the values of the

mean flow velocity V.

Compute and tabulate V2, Log hf, Log V, Log Re, Log F.

Given that

Graph 1. Plot Log hf against Log V

Graph 2. Plot Log F against Log Re

29

Flow Profile

From the above graphs assess the value of the critical velocity VC

below which flow is laminar.

Graph 3. For V > VC, plot hf against V

Graph 4. Fro V < VC plot hf against V

Determine the empirical relations hf = KVn from graph 1

Determine the empirical relations from graph 2.

Obtain the average value of F for turbulent flow in pipe from graph 3.

Obtain the value of from graph 4

CONCLUSION Does the experiment evidence indicate that two different flow regimes

are occurring?

Does the evidence support the relation for laminar flow and f

= 0.079, Re-0.25 for turbulent flow

Give reason for any discrepancies if experimental average value of

and f do not agree with value found from reference data.

30

Impact of Jets

CHAPTER SEVEN

EXPERIMENT 7.1

FLOW CONDITION

AIMTo observe Laminar, Transitional, Turbulent flow and there velocity

profile.

APPARATUS 1. Hydraulics bench

2. Osborne Reynolds apparatus

3. Vegetable dye

THEORY Laminar Flow: Is a steady conditional flow where the stream lines

are parallel. If the fluid is under this condition, the dye will be easily

identified as a solid core.

Turbulent Flow: Is an unsteady condition where the stream lines

interact causing shear plane collapse and mixing of the fluid. During

this condition, the dye will be totally mix up.

Transitional Flow: Is the period where the flow changes from

laminar to turbulent flow as the velocity of flow increases.

PROCEDURE Position the apparatus on the bench and fill the dye reservoir with dye

and lower the injector until it is just above the bellmouth inlet.

Close the flow control valve with bench inlet valve open slowly fill

head tank to the overflow level and close inlet valve.

31

Impact of Jets

To admit water to the flow visualization pipe open and close flow

control valve. The apparatus should be allowed to stand for at least

Fig

. 7.

1 O

sbor

ne

Rey

nol

ds A

ppar

atu

s

32

Impact of Jets

ten minutes before proceeding. Open the inlet valve slightly until

water trickles from the outlet pipe.

Fractionally open the control valve and adjust dye control valve until

slow flow with dye indication is achieved. When the flow rate is low,

the dye is drawn through the centre of the pipe. If the flow rate is

constantly increased, the flow rate produce eddies in the dye until the

dye completely disperses into the water.

For the velocity profile, open the dye reservoir needle for a drop of

dye to deposit in the pipe and you will observe that the drop will take

a three dimensional paraloid profile.

33

Impact of Jets

EXPERIMENT 7.2

OSBORNE REYNOLD’S EXPERIMENT

AIMTo reproduce the classical experiments conducted by Professor

Osborne Reynolds concerning fluid flow condition


2. Osborne Reynolds Apparatus

3. Measuring cylinder

4. Stop watch,

5. Vegetable Dye

6. Thermometer

See fig. 7. 1 above

THEORY Internationally, Reynolds number Re is recognised as a criterion

for denoting fluid flow condition

PROCEDURE Measure the temperature of the water. Slightly open the inlet

valve until water trickles from the outlet pipe. Fractionally open

the control valve until slow flow with dye indication is achieved.

Measure and note the flow rate. Repeat the experiment for

increasing flow rate by opening the flow control valve. Take a

specific measurement of flow rate at the critical condition.

34

Impact of Jets

Also repeat the procedure for decreasing flow rates, taking a

specific measurement of flow at the critical condition.


Visual dye condition Volume of water Time

Internal diameter of visualization pipe=

Temperature of water =

Viscosity of water =

Calculate volume flow rate and Re for each setting. Compare flow

conditions indicated by dye stream with value of Re

CONCLUSION Do the results obtained agree with the statement under analysis if

not account for any discrepancies.

35

Flow Visualization

CHAPTER EIGHT

EXPERIMENT 8.1

OPEN CHANNEL FLOW VISUALIZATION

AIMTo demonstrate phenomena associated with open channel flow.


2. Flow visualization channel

THEORY The primary purpose of this piece of apparatus is to demonstrate

visually a wide range of hydraulic effects associated with flow in

open channels. The intention is to complement lecturers

associated with the subject and not to form the basic for

theoretical analysis. No theoretical analyses or detailed

procedures are included. However, any of the effects may be

studied independently in detail.

PROCEDURE The apparatus should be installed over the bench top open

channel. It is important that the apparatus is sited as far as

possible from the volumetric tank, along the channels, to ensure

that water discharging from the apparatus is contained within the

volumetric tank. Connect the inlet pipe to the bench supply and

open the bench flow control valve.

36

Flow Visualization

37

Flow Visualization

The overshot weir may be adjusted in height by releasing both the

38

Flow Visualization

39

Flow Visualization

The overshot weir may be adjusted in height by releasing both the

thumb screw and the screw on the weir support. The plate may be

moved to the required position. The two screws should be re-

tightened to compress the sealing gasket. The undershot weir is a

push fit and height may be adjusted by sliding up or down.

Open channel hydraulics demonstrations include the following:

1. Discharge beneath a sluice gate (undershot weir).

2. Drowning of a sluice by an obstacle downstream (broad

crested weir).

3. The Hydraulic Jump, i.e. energy degradation in transition

from fast to slow flow.

4. Fast and slow, flow over a broad crested weir.

5. Fast and slow flow over a narrow crested weir.

40

Flow Visualization

EXPERIMENT 8.2

VISUALIZATION OF FLOW OVER OR AROUND

IMMERSED OBJECT

AIMTo visualize the flow pattern over or around an object immersed

in a fluid.


2. Flow visualization channel

3. Vegetable dye.

THEORY The primary purpose of this piece of apparatus is to demonstrate

visually a wide range of hydraulic effects associated with flow in

open channels. The intention is to complement lecturers

associated with the subject and not to form the basic for

theoretical analysis. No theoretical analyses or detailed

procedures are included. However, any of the effects may be

studied independently in detail.

PROCEDURE The apparatus should be installed over the bench top open

channel. It is important that the apparatus is sited as far as

possible from the volumetric tank, along the channels, to ensure

that water discharging from the apparatus is contained within the

volumetric tank. Connect the inlet pipe to the bench supply and

open the bench flow control valve. Models used in the channel

should be positioned using the tongs provided and installed by the 41

Flow Visualization

appropriate retaining screw. A blanking plug is provided for each

of the holes on the wall and floor when not in use.

The flow visualization technique involves the use of dye injected

at the hypodermic tubes. In operation, the overshot weir should

42

Flow Visualization

be raised fully and the undershot weir should be removed. The

model under investigation should be installed on its retaining

screw and the dye injection system installed in its retaining clip.

The dye reservoir should be filled with vegetable dye. Flow rate

through the channel should be adjusted at bench control valve.

Density of the dye streams may be adjusted using the control

valve at the base of the reservoir. With the overshot weir in the

raised position, the channel will run full of water enabling flow

patterns around and over submerged objects to be demonstrated.

DEMONSTRATIONS Demonstrations include flow around small or large cylinders and

symmetrical or asymmetrical aerofoils. Patterns of flow over

submerged broad and narrow crested weirs may also be demonstrated.

43

Impact of Jets

CHAPTER NINE

EXPERIMENT 9.1IMPACT OF JETS

AIMTo investigate the validity of theoretical expression to the force

exerted by jet on targets of various shapes. e.g. jet of water

directed on the vane of turbine with an output of 100,000 H.P and

with efficiency of 90%

APPARATUS 1. Jet impact apparatus2. Hydraulic bench3. Flexible hose4. Stop watch5. Vernier caliper 6. Weight

THEORY If a jet of fluid at the rate of 0m3/s along the x-axis with velocity V0

m/sec and is deflected by it tangent through angle B so that the

fluid leaves the tangent with velocity V1m/sec inclined at an angle

B to the axis, then the force F on the tangent in the direction of x is

equal and opposite to the force in the direction of x on the jet.

F = Q(V – Vcos B)

But

For the case of a flat plate, assume B = 900, so that

Since cos 900 = 0

44

Impact of Jets

Since the case of hemispherical tangent assume b = 1800

so that cosB = 1

.

45

Impact of Jets

For the case of a 1200 target, assume B= 1200 and Cos B = hence

PROCEDURE

Fig

. 9.1

Im

pact

of

Jet a

ppar

atu

s

46

Impact of Jets

First level the apparatus. Set the lever to the balanced position (as indicated by the tally) by placing the jockey weight at its zero position and then adjusting the knurled nuts above the spring. Admit water through the bench supply valve and centralize the jet on the flat plate by adjusting the four screws at the base. This screw adjustment should be done simultaneously by equal amount in opposite directions. Increase the rate of flow to the maximum and note the jockey weight which restores the lever to the balanced position, measure the discharge volume in the tank. Take six readings with roughly equally spaced positions of the jockey weight. Repeat the experiment using the 1200 target and the hemispherical target.The diameter of the nozzle, the height of the vane above the tip of the nozzle where the lever is balanced, the distance between the centre of the vane and the pivot of the lever, and the jockey weight

should be noted.


1. Results should be tabulated as follows:-

Mass on weight pan

Volume of water Time Flow rate

Q

Q2

Nozzle diameter = g = 9.81 m/s2,

=

2. Repeat table for 1200 target and hemispherical target.47

Impact of Jets

3. For each target plate, compute and tabulate Q and Q2 and plot

mass M on weight pan against Q2 and measure the slope.

4. From the analysis, the slopes of the graph should be as follows

Flat target

1200 ,,

Hemispherical target

Account for any discrepancies between the slopes obtained from

the measured values and the theoretical slopes.

48

Pressure Gauge Calibration

CHAPTER TEN

EXPERIMENT 10.1PRESSURE GAUGE CALIBRATION

AIM:To accurately calibrate a Commercial Bourdon tube pressure

gauge using a dead weigh tester.

APPARATUS:Equipment consists of a stainless steel piston which is free to

move vertically in a closely fittings brass cylinder. A transparent

flexible hose connects the cylinder to the pressure. This gauge is

of the Bourdon tube type and, like the cylinder, is mounted on the

cast base of the unit integral with the piston is a loading plat-form

upon which known weights are placed during test. All air is

expelled from the system by means of a purge hole in the upper

part of the cylinder.

THEORY: Gauge reading can be shown as a function of true (applied)

pressure. Gauge error can also be shown as a function of true

pressure. By graphically representing the results in this way, the

two possible kinds of gauge error-that due to combination of

hysteresis, friction and backlash and that due to graduation errors

can be shown.

49


PROCEDURE: Remove the piston and completely fill the system with water. Ensure

that all air has been purged by tilting the unit. Replace the piston.

Fig. 10.1 Pressure gauge calibration apparatus

Add weights in increments of kg. And at each increment observe

the pressure gauge reading. Do not apply more than 6kg weight50


on the calibration platform. During the test, slightly rotate the

piston to avoid sticking. Decrease the weights in decrement of

kg. And at each decrement observe the pressure gauge reading.

Note the weight of the piston and its cross-sectional area.

PRESENTATION OF RESULT AND CALCULATIONS1. Reading should be tabulated as follows:

Weight added to piston (kg)

Total load on piston (kg)

True pressure kg/mm2

Gauge reading (bar)

Increasing pressure

Decreasing pressure

2. Plot a graph of gauge reading against true pressure (Pressure

gauge calibration).

3. Plot a graph of gauge error against true pressure

(Gauge error = True pressure Gauge reading).

4. Comment on the Results obtained.

51

Losses in Bends

CHAPTER ELEVEN

EXPERIMENT 11.1 LOSSES IN PIPE BENDS

AIM To determine losses in small bore piping systems.

APPARATUS: 1. Hydraulic bench

2. Losses in bend apparatus

3. Stop watch

Fig. 11.1 Losses in bends apparatus

DARK BLUE CIRCUIT1. Gate valve

2. Standard Elbow bend.

3. 90° Mite bend

4. Straight pipe

52

Losses in Bends

LIGHT BLUE CIRCUIT5. Globe valve

6. Sudden expansion 13.7mm to 2 diameter

7. Sudden 26.4mm to 13 diameter

8. 152.4mm 900 radius bend

9. 101 .6mm 900 radius bend

10. 50.8mm 90° radius bend

THEORY:For an incompressible fluid flowing through a pipe, the following equations apply: Q = A1V1 =A2V2 (continuity)

(Bernoulli)

Where hl12 is the head loss1. The head loss along a length L of a straight pipe of constant

diameter d is given by where f = friction factor

2. Head loss at a sudden expansion is

3. Head loss at a sudden contraction is given by

where K depends on the ratio

4. Head loss due to a bend , K depends On

ratio

5. Head loss due to a valve where K depends upon

the type of valve and the degree of opening.

PROCEDURE:Open fully the water control valve on the hydraulic bench. With the globe valve closed, open the gate valve fully to obtain

53

Losses in Bends

maximum flow through the Light Blue circuit. Record the readings on the piezometer tubes and the U-tube. Collect a sufficient quantity of water in the weighing tank to ensure that the weighing takes place over a minimum period of 60 seconds. Repeat the above procedure for at least six different flow rates; obtain by closing the gate valve, equally spaced over the full flow range.Record the water temperature in the sump tank of the hydraulic bench each time a reading is taken. Close the gate valve, then open the globe valve and repeat the experimental procedure for the Dark Blue circuit.Close both the globe valve and gate valve before switching off the pump.


1. Results should be tabulated as follows:

a. Dark Blue Circuit

Test no. Time to collect 15kg water (sec)

Piezometer tube readings (cm) water

U-Tube (cm) Hg

1. 1 2 3 4 5 6 Gate valve2.

b. Light blue circuit

Test no. Time to collect 15kg water (sec)

Piezometer tube readings (cm) water U-Tube (cm) Hg

1. 7 8 9 10 11 12 13 14 15 16 Globevalve

2.2.(i) For the straight pipe, obtain the following relationship

(a) Head loss as a function of volume flow rate.

(b) Friction factor as a function of Reynolds Number.

(ii) For sudden expansion compare the measured rise in

head with the rise calculated on the assumption of

head loss.

54

Losses in Bends

(iii) For sudden contraction, compare the measures fall in

head with the fall calculated on the assumption of head

loss given by

(iv) Obtain values of loss coefficient K for the pipe

55

Steady Uniform Flow

CHAPTER TWELVE

EXPERIMENT 12.1STEADY UNIFORM FLOW

AIMIn most flow problems it is often necessary to predict the rate of

flow through a channel of known physical characteristic (size,

shape, slope, roughness etc.). In this experiment, the theoretical

and empirical relationships of these quantities are compared with

measured values in the channel for steady uniform flow.

APPARATUS:1) 5 metre inclinable flow channel

2) Adjustment sluice Gate/weir

3) Vernier depth gauges

4) Weights

5) Thermometer

THEORY The Chezy equation for steady uniform flow in a channel is given by

Where V = Velocity of flow C = Chezy coefficient

i = slope of channel

Where n = Roughness coefficient.

Where = Density of fluid, = viscosity of fluidV = mean velocity of flow, I = characteristics length

= m for open channel

56

Steady Uniform Flow

PROCEDURE:Set the sluice gate in the closed position and approximately half

fill the channel with water close the delivery valve before

stopping the pump so that W is retained in the channel While

allowing the water to settle, check that the instrument guide rails

are parallel to the channel base by using gauges about 250cm

(100ins.) apart in the mid-length of the channel and tilt the

channel using the hand wheel and screw arrangement until the

depth of water is greater at the down-stream depth gauge

than the upstream one. The channel bed now has a gradient of

.

Open the sluice gate and switch on the pump. Adjust the position

of the sluice gate and the flow rate to obtain a uniform depth of

flow of about 1.25cm over the mid-length of the channel, when

satisfied that the flow is uniform and steady, take measurement of

the flow rate using the weighing mechanism and stop-watch.

Record this against the depth of flow. Repeat the procedure for a

series of flow rates up to the maximum delivery of the pump.

Check the width of the channel with callipers. Also take the

temperature of the water.

PRESENTATION OF RESULTS AND CALCULATION 1. Readings should be tabulated as follows:2. Using Meaning formula and assuming values of n = 0.010,

0.009, 0.008 and 0.0075, calculate C.3. For the first and last tests, calculate the Reynolds number.4. Discuss your results.

57

Hydraulic Jump

CHAPTER THIRTEEN

EXPERIMENT 13.1THE CHANGE IN DEPTH AT A HYDRAULIC JUMP

AIM: To investigate the relationship between the flow rate in the

channel and the depth of flow on either side of a hydraulic jump.

APPARATUS:1) 5 meter inclinable flow channel

2) Adjustable sluice gate

3) Vernier Depth gauge

4) Stop watch

5) Weights.

THEORY: By applying the hydrostatic force and the momentum equations

across an hydraulic jump yields

Where d1 and d2 are depths upstream and downstream of jump.

q = flow per unit width

This equation may be rearranged to include the Froude Number Fr1 of the flow up stream of the Jump. From Continuity,

58

Hydraulic Jump

PROCEDURE. Set up the movable sluice gate about 1 meter from the inlet with the

channel bed set level. Adjust the flow rate and sluice gate opening to

give a range of flow depths upstream and downstream of the jump.

PRESENTATION OF RESULTS AND CALCULATIONS 1. Readings should be tabulated as follows:

Upstream

depth d1

Downstream

depth d2

Quantity W(kg)

Time to

collect

water (sec)

d-

1+

d2

d1d2(d1+d2)

2. Plot a graph of depth variation across a hydraulic jump with

quantity.

i.e. d1d2 (d1+d2) vs

3. Discuss the results obtained

59

Hydraulic Jump

EXPERIMENT 13.2FLOW UNDER A SLUICE GATE WITH A HYDRAULIC

JUMP

AIM:In this experiment, a sluice gate is used to produce rapid flow in a

channel where otherwise the flow would be tranquil. As the flow

reverts from the rapid to tranquil state, a resultant deepening of

the water takes place and is referred to as a Hydraulic jump.

APPARATUS 1. 5M Inclinable flow channel

2. Vernier Depth Gauges

3. Movable sluice gates

4. Stop-clock

5. Weights

THEORY:The energy per unit weight or specific energy E of a fluid above

the base of a channel at a depth d is given by

E is a minimum at the critical depth dc when or

Emin = dc

At the minimum at the critical, the critical velocity

Vc is given by Vc =

The minimum value of E corresponds to a Froude Number of 11

which is the critical condition in determining whether a flow is

rapid or tranquil.

60

Hydraulic Jump

PROCEDURE:

Set up the channel with a small slope on the channel bed of .

Clamp the movable sluice gate to the guide rails at about 1 metre from

the inter end. Check to see that it is squarely placed across the channel

and sealed properly at the edges. Switch on the pump and adjust the

flow rate so that the water is about 102mm (4 ins) deep upstream of

the sluice gate

When the latter is about 38mm from the base of the channel.

Measure the flow rate with the weighing mechanism and stop watch.

Measure the depth of flow upstream of the sluice gate and at 75mm (3

ins) interval downstream.

PRESENTATION OF RESULTS AND CALCULATION 1. Results should be tabulated as follows:

Position Depth d E = d +

Upstream of Gate at Gate

75mm downstream of gate

150mm downstream of gate

2. Plot a graph of depth against specific Energy.3. Plot on another graph paper, depth of flow and specific Energy

against distance from the sluice gate.4. Comment on the position of Emin with respect to that of the

hydraulic jump.

61

Flow over a board

CHAPTER FOURTEEN

EXPERIMENT 14.1FLOW OVER A BROAD - CRESTED WEIR

AIM:To show that the flow over the top of a broad crested weir is

approximately critical

APPARATUS1. 5m inclinable flow channel

2. Depth gauges

3. 3 rectangular plated metal block

4. Stop-watch

5. Weights

THEORYFor a broad-crested weir in a rectangular channel,

Since velocity upstream is small, in

negligible. Therefore E = d0 where do = d0 –d

so that

E = Specific Energy du = Upstream depth of weir

dc = Critical depth do = du - d

d = Heights of weir q = flow per unit width

PROCEDURE:

62

Flow over a board

Adjust the channel bed to a shallow slope of . Place the 3 blocks

end to end about 1 metre from the outlet end of the channel. Adjust

the flow, rate through the channel to the maximum value for which the

flow over the crest is substantially parallel to the crest. Take readings

of the upstream depth du and the depth over the crest (dc + d), while

measuring the flow rate with the weighing mechanism and stop clock.

Reduce the flow rate and repeat the readings.

PRESENTATION OF RESULTS AND CALCULATION 1. Results should be tabulated as follows:

Critical depth

Depth upstream du

Depth at weir dc + d

W kg Time sec

q do dc

2. Plot a graph of calculated critical depth against depth over weir.

3. Comment on the results obtained.

63

Flow through a venture flume

CHAPTER FIFTEEN

EXPERIMENT 15.1FLOW THROUGH A VENTURE FLUME

AIM:To compare the practical and theoretical profiles of the water surface through the venturi and find a coefficient of discharge for the venturi.

APPARATUS:The venturi is made by fitting a pair of double wedge plate inside the channel. The plates are made of 12.7mm ( ½ in.) thick clear Perspex and are shaped so that each tapered section and the throat are 14.3mm(4½ ins) long and in the directions of flow. The plates are held in position at the sides of the channel by a screwed aluminium spacer, which is fitted in the throat above the level of the water surface.

THEORY: For a rectangular cross section flume.

Where E = Specific Energyd = Depth of flowV = Mean Velocity of flow b = Breadth of flowQ = Quantity (rate of flow)

If the flow conditions are critical in the throat, then

Where is the depth of flow in the throat. If there is a large change in the cross sectional area between the upstream and the throat sections, then the upstream velocity head may be neglected and equation (2) becomes

64


Where do = upstream depth.If we consider the velocity distribution to be uniform at all sections then we may combine (1) and (2) or (1) and (3) so that

Where = Breadth at the throat

Or ………………………………….(4)

Putting E d0

…………………………….……….(5)

or ………………………………….(6)

Where Cd is the coefficient of discharge.PROCEDURE:

Adjust the channel bed to a slope of 1 in 400. Insert and secure the

venturi plates in a position about meter from the outlet end of

the channel. Care should be taken to see that the plates are positioned exactly opposite to one another so that throat positions corresponds. Switch on the pump and adjust the flow rate to the maximum for which the critical condition exists in the

throat (i.e. the depth at some point in the throat should be of

that upstream of the venture). When the flow rate is set, use the depth gauges to measure the depths of flow at 25mm intervals along the length of the venture. Repeat the procedure for series of flow rates being careful that the flow is always critical in the throat.

PRESENTATION OF RESULTS AND CALCULATIONS1. Reading could be recorded as

65


2.5c

m U

pstr

eam

Sta

rt o

f ve

ntur

e (A

)

2.5c

m f

rom

(A

)

5.0c

m f

rom

(A

)

7.5c

m f

rom

(A

)

10cm

fro

m (

A)

12.5

cm f

rom

(A

)

15.0

cm f

rom

(A

)

17.5

cm f

rom

(A

)

20.0

cm f

rom

(A

)

22.5

cm f

rom

(A

)

25.0

cm f

rom

(A

)

27.5

cm f

rom

(A

)

30.0

cm f

rom

(A

)

32.5

cm f

rom

(A

)

35.5

cm

fro

m (

A)

37.5

cm

fro

m (

A)

40.0

cm f

rom

(A

)

2. Using the Upstream reading, calculate E from

With this derive an expression for each flow rate such that

---------------------------------(b)

Where

Compute values of the left hand side of equation (b) for various values of d and plot these against d.3. Draw the theoretical and practical water surface pr through the

venturi for a given flow rate.4. Using equations (4) and (5) determine the coefficient of discharge

for each flow rate. Draw a graph of theoretical discharge

against practical discharge Qp and comment on your results.

66

Characteristics of Pump(s) at Single Speed

CHAPTER SIXTEEN

EXPERIMENT 16.1PERFORMANCE CHARACTERISTICS OF A SINGLE

PUMP AT A SINGLE SPEED

AIM:To determine the head/flow rate characteristic of a single

centrifugal pump at a single speed.

APPARATUS: 1. Hydraulics bench

2. Series/parallel pump test accessory.

Power sw itch

Hydraulics bench

Fig. 16.1 Series/parallel pump test accessory THEORY:

In this experiment we are concern with head/flow rate

relationship. If we note the inlet and outlet head, the total head

will be the difference between outlets head and the inlet head.

67


From our gauge reading, if the inlet head is P1 and the outlet

head is P2, then Total head = P1-P2

PROCEDURE With the auxiliary pump on the floor of the left hand side of the hydraulics bench, position the apparatus manifold in the bench channel and connect the bench with the apparatus using the appropriate hoses as shown. Switch on the electrical power supply. Open the drain valve and open the discharge control valve. Switch on the pump.Record inlet pressure, outlet pressure and flow rate using the volumetric tank. Close discharge valve slowly. Tabulate your result at different discharge.

PRESENTATION OF RESULT AND CALCULATIONManifold

pressure mH2OInlet

m.H2ODatum head correction m

Total Head

m.H2O

Vol.(l)

Time(sec.)

Flow rate Q l/s

0 0.82.0 0.84.0 0.86.0 0.88.0 0.810.0 0.812.0 0.814.0 0.816.0 0.8

Plot a graph of head against flow rate

68


EXPERIMENT 16.2PERFORMANCE CHARACTERISTICS OF SIMILAR PUMP IN PARALLEL

AIM:To determine the head/flow rate characteristics of two similar pumps operating in a parallel at the same speed.


2. Series/parallel pump test accessory

Pow er sw itch

Hydraulics bench

Fig. 16.2 Series/parallel pump test accessory (with Y-connector i.e. in parallel)

THEORY: When two or more similar pumps are connected in parallel, the head across each pump is the same but the flow rate Q is showed equally between the pumps. It should be noted that flow rate does not increase according to the number of pump switch on.

PROCEDURE: With the auxiliary pump on the floor of the left hand side of the hydraulics bench, position the apparatus manifold in the bench channel and connect the bench with the apparatus using the

69


appropriate hoses as shown. Switch on the electrical power supply. Open the drain valve and open the discharge control valve. Switch on the pump.Record inlet pressure, outlet pressure and flow rate using the volumetric tank. Close discharge valve slowly. Tabulate your result at different discharge.

PRESENTATION OF RESULT AND CALCULATION Manifold

pressure mH2OInlet

m.H2ODatum head correction m

Total Head

m.H2O

Vol.(l)

Time(sec.)

Flow rate Q l/s

0 0.82.0 0.84.0 0.86.0 0.88.0 0.810.0 0.812.0 0.814.0 0.816.0 0.8

Plot a graph of head against flow rate

Compare this graph with graph of experiment 16.1

Comment on your flow rate and give reasons why the flow rate

does not increase in proportion to the number of pumps used.

70


EXPERIMENT 16.3

PERFORMANCE CHARACTERISTICS OF TWO SIMILAR PUMP IN SERIESAIM:

To determine the head/flow rate characteristics of two similar

pumps operating in series at the same speed.


2. Series/parallel pump test speed

Power switch

H yd raulics b en ch

Fig. 16.3 Series/parallel pump test accessory (in series)

THEORY:If two or more similar pumps are connected in series, the discharge passes through each pump in turn and undergoes a head boost

D = Number of pumpsH = total head

It two similar pumps are connected in series will give a combined pump characteristics of twice the head P1 + P2

PROCEDURE:

71


With the auxiliary pump on the floor of the left hand side of the hydraulics bench, position the apparatus manifold in the bench channel and connect the bench with the apparatus using the appropriate hoses as shown in fig. 16.3. Switch on the electrical power supply. Close bench control valve, close discharge valve, and switch on pump. Open discharge valve. With the discharge valve fully open allow the pumps to stabilize for a few minutes and notice that there will be no pressure reading as the valve is fully open.Close the discharge valve slowly to obtain a convenient pressure gauge reading of about 0.5bar. Record pressure and compound gauge readings using the volumetric tank determine flow rate. Repeat above procedure at different pressure until discharge valve is fully closed.


Times

Vol.l

Flow rate Q

Pressure Compound Velocity head

correction

Datum head

correction

Total head

mH2Ol/s m3s-

1Bar mH2O Bar mH2O

Area of hose = 7.85 × 10-5m2

Velocity Head = , but , g = 9.8ms-2

Distance between gauge centres = (Datum head)Total head = (pressure + velocity head + datum head) – CompoundPlot a graph of total head against flow rate.

72

Characteristics of Pump(s) at Varying Speed

CHAPTER SEVENTEEN

EXPERIMENT 17.1PERFORMANCE CHARACTERISTICS OF A PUMP

AIM:To determine the relationship between head discharge, power

efficiency and speed for a centrifugal pump at various speed.


2. Pump characteristics test accessory

Fig. 17.1 Pump characteristics test accessory

THEORY: The performance of any pump working at a fixed speed can be

represented by the following relationship

1. Total Head (H) against Discharge (Q)

2. Input Power (P) against Discharge (Q)

3. Efficiency ()against Discharge (Q)

73


The above relationship plotted together on a graph sheet is

called the performance characteristics and is always advisable

to plot them on a common base line of discharge (Q).

Total head = Inlet pressure – Discharge pressure (mH2O)

Input Power = Volts ×Amps (W)

Efficiency % =

Water power = gHQ (W)

Where = 1,000kg/m3

g = 9.81 m/s2

PROCEDURE: Position the apparatus manifold block on the working channel

of the hydraulics bench and the pump set on the floor at the left

hand side of the bench. With the appropriate hoses connect the

apparatus to the bench drain valve. Switch on the electrical

supply, and open the drain valve and the discharge control

valve. Switch on pump to run on a speed of 2,000r.p.m

Tabulate reading on gauge and meters, determine flow rate.

Slowly close discharge valve to give a convenient reading on

the gauge and record new reading until valve is totally closed.

Repeat the above procedure for a pump speed of 2,500r.p.m

and 3,000r.p.m

PRESENTATION OF RESULT AND CALCULATIONS

74


Tabulate result as shown belowR

.P.M

Suction head

(mH2O)

Pressure head

(mH2O)

Gauge correction

head

Total head

(mH2O)

Vol

l

Tim

es

Q l

/s

Q

m2 /s

Water power P(w)

Am

ps

Vol

ts

Power input

W

Eff

icie

ncy

%

2000 0.8

2000 0.8

2000 0.8

2000 0.8

2500 0.8

2500 0.8

2500 0.8

2500 0.8

3000 0.8

3000 0.8

3000 0.8

3000 0.8

Plot the following performance characteristics curve for each speed

Total head (H) against Discharge (Q)

Input power (P) against Discharge (Q)

Efficiency () against Discharge (Q)

From your graph, at what speed was the operating point of the

pump achieved?

Comment on the effect of suction head on the performance of the

pumps.

See appendix 1 for the performance curve

75

Characteristics of Reciprocating Pump

CHAPTER EIGHTEEN

EXPERIMENT 18.1PRESSURE HEAD AND FLOW RATE AT VARIOUS

SPEED OF A RECIPROCATING PUMP

AIM:To investigate the relationship between pressure head and flow

rate at various reciprocating pump speeds.

APPARATUS: 1. Arm field ram pump test bench

2. Stop watch

Fig. 18.1 Reciprocating Pump

PUMP SPEED RATIO

Pump/Motor pulley teeth ratio

Maximum pump speed Motor @ 1450 rev.min

Bourdon pressure guage

72.14 282 rev/min 0-70m.H2O

76


Fig. 18.2 Arm field ram pump test bench

PROCEDURE: With the delivery gate valve fully open, switch on the test rig and

raise the motor speed to maximum. Note the reading on the

pressure gauge at this point. Now slowly close the delivery gate

valve and STOP when the pressure gauge reads 5m.H2O.

NOTE: The delivery gate valve must not be fully closed with the pump

running as serious damage could occur to the equipment.

Note the difference between the maximum pressure reading and minimum pressure reading (5m.H2O) and select six equi-spaced points throughout the pressure range, which will be the pressures at which flow will be measured. The actual pressure head of the

77


pump is the difference between the pressure gauge reading in m.H2O and the vacuum gauge reading in m.H2O, at a particular rate of flow.At each selected pressure reading, measure the rate of flow using the graduated sight glass on the volumetric tank and the stopwatch. Tabulate this data in the Results Section below.The above procedure is now repeated at two other speeds, e.g. 1000 rev/min and 500 rev/min and the results are tabulated.


Pump speed =

= Readings Pressure m.H2O Vacuum m.H2O Head m.H2O Flow rate l/sec123456

Pump Speed:………………….

Readings Pressure m.H2O Vacuum m.H2O Head m.H2O Flow rate l/sec123456

Pump speed:………………..

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Readings Pressure m.H2O Vacuum m.H2O Head m.H2O Flow rate l/sec

123456

CONCLUSION From the results table construct a family of three graphs for each

speed using common axes of pump head (vertical axis) against flow

rate (horizontal axis).

Compare the characteristics curves and comment upon the

flow/pressure relationship at different speeds.

Suggest any advantages or disadvantages of the ram type pump.

79


EXPERIMENT 18.2RELATIONSHIP BETWEEN PRESSURE HEAD, FLOW RATE, TORQUE, AND POWER OF A RECIPROCATING PUMP

AIM:To investigate the relationship between pressure head, flow rate,

torque, power consumed for a reciprocating pump.

APPARATUS: 1. Arm field ram pump test bench (see fig. 18.2)

2. Stop watch.

PROCEDURE 1. Ensure that the dynamometer motor torque arm has been

correctly set to zero.2. With the delivery gate valve fully open, switch on the test rig

and set the motor speed to maximum 1450 rev/mm.3. Note the reading on the pressure gauge at this point.4. Now slowly close the delivery gate valve and STOP when the

pressure gauge reads 5m.H2O NOTE: The delivery gate valve must not be fully closed with the pump running as serious damage could occur to the equipment.

5. Note the difference between the maximum pressure reading and minimum pressure reading (5m.H2O and select six equi-spaced points throughout the pressure range, which will be the pressures at which flow will be measured. The actual pressure head of the pump is the difference between the pressure gauge reading in m.H2O, and the vacuum gauge reading in m.H2O, at a particular rate of f low.

6. Adjust the delivery gate valve to the first of the selected pressure gauge readings.

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7. Measure the rate of flow using the graduated sight glass on the volumetric tank and the stopwatch. Record flow rate in results.

8. At this particular flow rate, place weights on the weight hanger to return the beam to the balanced (horizontal) position. Note the Torque in the results table.

9. Repeat operations (f) and (h) above, for the five other selected pressure readings.

10. Repeat operations (b) to (i) above for two other motor speeds as required, say 1000 rev/mm and 500 rev/mm.

PRESENTATION OF RESULTS AND CALCULATIONSAll data gathered during the test must be tabulated on the results sheet.

CALCULATIONS Torque T = L.g.W

Where T = Torque Nm L = torque arm length (metres) g = 9.81 m.sec-2

W = load (kg)

Input Power P =

Where P = Power in watts N = Pump rev/mmT = Torque N.m.

Note: The actual pump speed may be calculated using the pump/motor pulley ratio as follows:

Pump Speed = Motor Speed

Hydraulic Power (Pump output power) P/ = .g.Q.H/.10-3 Where P/ = Hydraulic power (watts)

= Density of water g = Gravity 9.81.sec-2

Q = Rate of flow 1/sec H/ = Pump head m.H2O

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1. Construct a family of curves for the various speeds at which the tests were carried out, using common axes of Pressure Head (vertical axis) against Flow Rate (horizontal axis).

2. Construct a family of curves for the various speeds at which the tests were carried out, using common axes of Pressure Head (vertical axis) against Torque (horizontal axis).

3. Construct a family of curves for the various speeds at which the tests were carried out, using common axes of Input Power (vertical axis) against Flow Rate (horizontal axis).

QUESTION1. Referring to the Power/Flow graph, should. the pump be

started with its flow control valve open, or closed? Explain why.

2. What are the disadvantages of the ram type pump when compared with centrifugal or gear type pumps?

3. Given that Efficiency = , show the most

efficient operating point for the pump at any one of the operating speeds chosen in the test.

4. State a suitable industrial application for this type of pump. Correlate the industrial application with the test data obtained.

Note: This results table is used for the testing of the pump at ONE speed only. If tests at other speeds are required, further copies of this sheet must be used.

Motor speed:………………….rev/min

Readings Pressurem.H2O

Vacuumm.H2O

Pump Head

m.H2O

Volume(l)

Time(sec.)

Flowl/sec

TorqueN.m

PowerWatts

123456

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83

Characteristics of Turbines

CHAPTER NINETEEN

EXPERIMENT 19.1PERFORMANCE CHARACTERISTICS OF PELTON IMPULSE TURBINE

AIM:To determine the operating characteristics of a pelton turbine at

various speeds.

APPARATUS:1. Hydraulics bench

2. Pelton impulse turbine

3. Tachometer

Fig. 19.1 Pelton impulse turbine

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THEORY Pump and turbine performance curves are derived in the same

ways. The speed is usually considered as a principle variable when

plotting power, efficiency, torque and discharge.

Mechanical power Pm = Torque angular velocity

= T, where T = Force radius (Nm)

and =

Water power = Where = density of water 1,000kg/m3

g = 9.81 m/s2

H = Inlet head mQ = Flow rate m3/s

Turbine Efficiency % =

PROCEDURES Position the pelton turbine on the hydraulic and connect the bench

supply to the apparatus. Clamp the tachometer and lift the band

brake assembly until it is off the brake drum. Switch on the bench

pump and fully open the bench control valve. Adjust spear control

valve until the maximum rev/min are indicated on the tachometer.

Measure rev/min, flow rate, and inlet pressure. Lower band brake

assembly over brake drum and adjust band until a convenient

reading is indicated on the right hand spring balance loads. Repeat

the procedures above at different applied loads and tabulate the

results.


Brake drum radius = 30 10- 3m

D ru m

W2 W1

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Total force = W2 – W1

Fig. 18.2

R.P.M (rad/s)

W1 (N) 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0W2 (N)

W1-W2 (N)

Drum radius

30 30 30 30 30 30 30 30 30 30 30 30 30 30

Torque (N/m)Pm (W)

Vol. (l)

Time (s)

Flow rate (m3/s)Pressure (mH2O)Pw (W)

Efficiency (%)

1. Plot a graph of power against rotor speed.

2. Plot a graph of torque against rotor speed.

3. Plot a graph of efficiency against rotor speed.

4. Plot a graph of discharge against rotor speed

5. What is the difference between pump and turbine

6. Comment on the graphs.

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Pow er

Pow er

Fig. 1. Head/ flow rate control for single centrifugal pump at single speed

H

Q

2 Pum ps1 Pum p

Pow erQ2

Q2

Fig. ii. Head/flow rate for two centrifugal pump in parallel

H

Q

2 Pum ps

1 Pum p

H2

H2

Fig. iii. Head/ flow rate control for two centrifugal pump in series Discharge

Operating point

Head

Power input

Efficie

ncy

Fig. iv. Performance curve for a centrifugal pump

Discharge

Torque Power

Efficiency

Rotor Speed

Fig. v. Performance curve for a Pelton turbine

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REFERENCE

Arm Field Instructional Manual, October 1988

Felix J. K. Ideriah: Fluid Machinery, MacMillan Press London (in Preparation)

J. F. Douglas; J.M Gasiovek; J. A. Swaffield, London Fluid Mechanics, Pitman Books Ltd. 1981.

John A. Robertson; Calyton L. Crowe Engineering Fluid Mechanics Washington State University Pullman. 2nd Edition

Lewitt. E. H; Hydraulics and Fluid Mechanics, Pitman and Sons Ltd. London (1966)

Walsaw A. C and Jobson D. A; Mechanics of Fluids, Longmans Green and Co. Ltd, London 1962

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Index

A

APPARATUS, 3, 5, 9, 12, 15, 33ARM FIELD RAM PUMP TEST BENCH,

72, 73, 76

B

BENCH, 2, 3, 5, 12, 15BENDS, 3BERNOULLI’S THEOREM, 17, 18BOURDON TUBE, 45BRAKE DRUM, 81BUOYANCY, 7

C

CENTRIFUGAL PUMP, 3CHEZY EQUATION, 52CIRCUIT, 50CRITICAL DEPTH, 58, 59

D

DISCHARGE, 37, 69, 70, 71DYE, 33

E

ENERGY, 57, 58, 60

F

FLEXIBLE HOSE, 41FLOW, 3, 19, 30, 35, 38, 40, 43, 64, 66, 68,

74, 75, 77, 78, 80, 81FLUID, 19, 83FRICTION, 3, 28, 50

G

GATE VALVE, 48, 50GAUGE, 45, 47, 71GRAVITY, 6, 77

H

HEMISPHERICAL TARGET, 44HOOK, 20, 23HYDRAULIC BENCH, 8, 17, 20, 23, 26, 41,

48

HYDROSTATIC, 3, 8, 9

J

JOCKEY WEIGHT, 7

L

LOSSES IN BEND APPARATUS, 48

M

MANIFOLD, 64, 66MASS, 11, 43METACENTRIC, 3, 5METRE, 5MOMENT, 8MOVABLE SLUICE GATES, 56

P

PONTOON, 7PUMP CHARACTERISTICS TEST

ACCESSORY, 69

R

ROUGHNESS COEFFICIENT, 52

S

SUMP, 3

T

TACHOMETER, 79TEMPERATURE, 34THERMOMETER, 26, 33, 52TUBE, 19, 50TURBULENT FLOW, 30

U

UPSTREAM DEPTH, 55, 58

V

VEGETABLE DYE, 30, 38VERNIER DEPTH GAUGES, 52VOLUMETRIC, 6, 15, 35, 38, 64, 66, 68,

74, 76

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Index

W

WATCH, 15, 17, 20, 23, 26, 33, 41, 48, 53, 54, 57, 58, 72, 76

WEIGHT, 1, 2, 6, 43, 44, 47, 56, 77WEIRS, 40

90

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