Fluid Mechanics 2 Lab Manual

ME-352L Fluid Mechanics Lab II

PRACTICAL HANDOUTS

DEPARTMENT OF MECHANICAL ENGINEERING

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Table Of Content

1. Energy Loses in Bends and Fittings ............................................................................................... 7

1.1. Introduction .................................................................................................................................... 7

1.2. Theory ............................................................................................................................................ 7

1.2.1. Characteristic of Flow through various Pipe Fittings and Valve Elbows: ...................................... 7

1.2.2. Short bend ....................................................................................................................................... 8

1.2.3. Sudden enlargement and sudden contraction ................................................................................. 9

1.2.4. Sudden enlargement ....................................................................................................................... 9

1.2.5. Sudden contraction ......................................................................................................................... 9

1.2.6. Gate valve ..................................................................................................................................... 10

1.3. General description ....................................................................................................................... 10

1.4. Experiment 1: Losses in Bends and Pipe Fittings ........................................................................ 12

1.4.1. Objective....................................................................................................................................... 12

1.4.2. Procedure ...................................................................................................................................... 12

1.4.3. Observations and calculations ...................................................................................................... 12

1.5. Experiment 2: Energy Losses through Gate Valve....................................................................... 13

1.5.1. Objective....................................................................................................................................... 13

1.5.2. Procedure ...................................................................................................................................... 13

1.5.3. Observation and calculation ......................................................................................................... 13

2. Flow over wiers ............................................................................................................................ 16

2.1. Introduction .................................................................................................................................. 16

2.2. Theory .......................................................................................................................................... 16

2.3. Technical specifications ............................................................................................................... 18

2.4. Experiment: To determine and comment on the coefficient of discharge. ................................... 19

2.4.1. Aim ............................................................................................................................................... 19

2.4.2. Procedure ...................................................................................................................................... 19

3. Pelton wheel turbine ..................................................................................................................... 21

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3.1. Introduction .................................................................................................................................. 21

3.2. Description ................................................................................................................................... 21

3.3. Theory .......................................................................................................................................... 22

3.3.1. Pelton wheel turbine ..................................................................................................................... 22

3.4. Experiment: Pelton Wheel Turbine .............................................................................................. 24

3.4.1. Aim ............................................................................................................................................... 24

3.4.2. Procedure ...................................................................................................................................... 24

3.5. Observations: ................................................................................................................................ 25

4. Pipe Friction Apparatus .......................................................................................... 27

4.1. Introduction .................................................................................................................................. 27

4.2. Theory .......................................................................................................................................... 27

4.2 For Turbulent Flow ....................................................................................................................... 28

4.3 Pipe Friction Apparatus ................................................................................................................ 29

4.4 Experiment : Pressure loss of Laminar flow and Turbulent Flow ................................................ 30

4.4.1 Aim ............................................................................................................................................... 30

Pressure loss of laminar flow is to be compared with turbulent flow. ..................................................... 30

4.4.2 Procedure ...................................................................................................................................... 30

5. Series and Parallel Pump .............................................................................................................. 34

5.1. Introduction .................................................................................................................................. 34

5.2. Specifications ................................................................................................................................ 35

5.3. General requirements .................................................................................................................... 36

5.4. Theory .......................................................................................................................................... 36

5.5 Dynamic Pumps............................................................................................................................ 36

5.5.1 Horizontal Single Stage Centrifugal Pump .................................................................................. 36

5.5.2 Pump Head versus Flow rate Curves for Centrifugal Pumps ....................................................... 37

5.5.3 Centrifugal Pump Connected in Parallel ...................................................................................... 39

5.5.4 Centrifugal Pump Connected in Series ......................................................................................... 39

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5.5.5 Impeller Types .............................................................................................................................. 40

5.5.6 Backward-curved Blades .............................................................................................................. 40

5.5.7 Forward-curved Blades ................................................................................................................ 40

Formula for Calculation of Variables ...................................................................................................... 41

5.6 General start-up procedures .......................................................................................................... 42

5.8 Experiment: characteristics of pump-in-series operation ............................................................. 43

5.8.1 Aim ............................................................................................................................................... 43

5.9 Experiment 2 ................................................................................................................................ 44

5.9.1 Aim ............................................................................................................................................... 44

5.9.2 Equipment Set Up ......................................................................................................................... 44

5.9.3 Procedures .................................................................................................................................... 44

5.9.4 Assignment ................................................................................................................................... 44

6 Axial flow Fan .............................................................................................................................. 46

6.1 Control unit ................................................................................................................................... 46

6.1.1 Main air flow tube ........................................................................................................................ 46

6.1.2 Orifice ........................................................................................................................................... 46

6.1.3 Flow regulator .............................................................................................................................. 46

6.1.4 Axial fan ....................................................................................................................................... 46

6.1.5 Damper ......................................................................................................................................... 46

6.2 Theory .......................................................................................................................................... 46

6.3 Types of fans ................................................................................................................................ 47

6.3.1 Centrifugal fans ............................................................................................................................ 47

6.3.2 Axial fans...................................................................................................................................... 47

6.4 Characteristic curve for axial fan .................................................................................................. 48

6.5 Experiment: Relation between differential pressure across fan and volume flow rate ................ 49

6.5.1 Aim ............................................................................................................................................... 49

6.5.2 Procedure ...................................................................................................................................... 49

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6.5.3 Observations and Calculations ..................................................................................................... 49

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Energy Losses in Bends

And Fittings

ME-352L Fluid Mechanics Lab II IST-MECH-EL-EXP01/01

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1. Energy Loses in Bends and Fittings

1.1. Introduction

The apparatus Losses in Bends and Fittings has been designed for students experiment on the

investigation of energy losses in pipe bends and fittings including valves. The equipment is

mounted on a free-standing framework supporting the test pipe work and instrumentation. These

pipe fittings are included: miter bend, 90o elbow, sweep bends (large and small radius),

contraction and enlargement.

1.2. Theory

When fluid flow through typical pipe fittings such as an elbow or a bend, this result in energy

loss. These energy losses, which are termed as minor losses, are primarily due to the change in

the direction of flow and the change in the cross-section of the flow path typically occurs in

valves and fittings. Experimental techniques are used to determine minor losses. Tests have

shown that the head loss in valves and fittings is proportional to the square of the average

velocity of the fluid in the pipe in which the valve or fitting is mounted. Thus the head loss is

also proportional to the velocity head of the fluid.

1.2.1. Characteristic of Flow through various Pipe Fittings and Valve Elbows:

45degree elbow and 90 degree elbow Figures below show flow round a 45 degree elbow and a

90 degree below, which has a constant circular cross section respectively.

Figure 1: Elbows (90 degree and 45 degree)

The value of loss coefficient K is dependent on the ratio of the bend radius, R to the pipe inner

diameter D. As this ratio increase, the value of K will fall and vice versa.

90degree elbow 45 degree

elbow


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1.2.2. Short bend

Losses of head in bends are caused by the combined effects of separation, wall friction and the

twin-eddy secondary flow. For large radius bends, the head loss is predominant by the last two

effects, whereas for short bends, it is more dominated by separation and secondary flow. Value

of K is dependent on the shape of passage (determined by θ and R/D) and Reynolds number.

LONG BEND SHORT BEND

Figure 2: Bends (long and short)

Figure 3: Bend Fittings


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1.2.3. Sudden enlargement and sudden contraction

1.2.4. Sudden enlargement

As a fluid flows from a smaller pipe into a larger pipe through a sudden enlargement,

its velocity abruptly decreases, causing turbulence that generates an energy loss. But due to

diffuser effect pressure increases

Figure 4: flow through sudden enlargement

1.2.5. Sudden contraction

As the streamlines approach the contraction, they assume a curved path and the total stream

continues to neck down for some distance beyond the contraction. This section where the

minimum flow area occurs is called the vena contracta. Beyond the vena contracta, the flow

stream must decelerate and expand again to fill the pipe. The turbulence caused by the

Figure 5: fluid flows through sudden contraction


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contraction and the subsequent expansion generates energy loss, which is given by fig 5.

1.2.6. Gate valve

Gate valve is one of several types of valves that is used to control the amount of flow. The value

of loss coefficient K of a gate valve is dependent on the position of the valve. Fluids flow

through fully open gate valves in straight line paths, thus there is little resistance to flow and the

resulting pressure loss is small. For fluid flow through partially opened gate valve, resistance to

flow will be greater and thus produces a larger value of K.

1.3. General description

Figure 6: Apparatus for Energy loses in bends and fittings

1.3.1 Description and assembly

1. 90o Elbow 6. Pressure Gauge

2. Sudden Enlargement 7. Gate Valve

3. Sudden Contraction 8. Pressure Gauge

4. 45o Elbow 9. 90

o Elbow

5. 90o Bend

11. Water outlet

10. Water Inlet


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Figure 7: Tubing’s of manometers.

Note: Pipe and fittings sizes are as follows:

Pipe Outer Dia = 21.5mm

Pipe inner Dia = 14mm

Enlarged Section

Outer Dia = 33.5

Inner Dia = 25.4mm

Fittings Inner Dia = 14mm


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1.4. Experiment 1: Losses in Bends and Pipe Fittings

1.4.1. Objective

To measuring the losses in the fittings related to flow rate and calculating loss coefficients

related to velocity head.

1.4.2. Procedure

1. Attach pipe with hydraulic bench fitting and inlet of apparatus.

2. Open the gate valve 4½ turns. Now start the hydraulic bench pump and slowly open the

valve. Open valve to that extent so that all tubes of manometer get flushed out.

3. Now slowly close the valve so that all a tubes of manometer have water in them.

4. If water level in the manometer is too high use the degassing valve to lower it.

5. Now at different flow rates (adjusted by the hydraulic bench valve) note the manometer

readings.

6. Calculate the flow rate with a stop watch and hydraulic bench tube.

1.4.3. Observations and calculations

No.

of

Obs.

Volume V

(litres)

Time T

(sec)

Flow rate Q

(m³/s)

Manometer Reading(mmH20)

1 2 3 4 5 6 7 8 9

1.

2.

3.

4.

5.

Table 1: Observations and calculations

No.

of

Obs.

Flow

rateQ

(m³/s)

Velocity

in small

bore pipe

(m/s)

4Q/πd²

Velocity

head

(mH2O)

v²/2g

Differential Piezometer Head h (mmH2O)

90

elbow

Sudden

enlargement

Sudden

contraction

45

elbow

Short

bend

1.

2.

3.

4.

5.

Table 2: Observations and calculations


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1.5. Experiment 2: Energy Losses through Gate Valve

1.5.1. Objective

To measuring the losses through gate valve related to flow rate and calculating loss coefficients

related to velocity head

1.5.2. Procedure

1. Place apparatus on bench, connect inlet pipe to bench supply and outlet pipe into volumetric

tank.

2. With the bench valve fully closed and the discharge valve fully opened, start up the pump

supply from hydraulic bench. Slowly open the bench valve until it is fully opened.

3. When the flow in the pipe is steady and there is no trapped bubble, start to close the bench

valve to reduce the flow to the maximum measurable flow rate.

4. Slowly open the gate valve to 2 turns position and measure and record the differential

pressure reading across the valve.

5. Then, measure the flow rate with the volumetric tank. Repeat the differential pressure

measurement with different decreasing flow rates.

6. The flow rates can be adjusted by utilizing the bench flow control valve. Plot graph

differential piezo meter head, h against velocity head for the gate valve and determine the

loss coefficient. The experiment can be repeated with different gate valve opening.

1.5.3. Observation and calculation

No. of

obs.

Volume

V (litre)

Time T

(sec)

Flow rate

(m³/s)

Differential

pressure

across

valve

(psi)

1.

2.

3.

4.

5. Table 3: Observation and Calculation


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No. of

obs.

Flow rate,

Q

(m3/s)

Velocity in

small bore

pipe, v

(m/s)

4Q/πd²

Velocity

head,

(m H2O)

v²/2g

Differential

pressure

across valve

(m H2O)

Valve

position

1.

2.

3.

4.

5. Table 4: Observation and Calculation

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Experiment Guide

FLOW OVER WEIRS

APPARATUS

ME-352L Fluid Mechanics Lab II IST-MECH-FOW-EXP02/00

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2. Flow over wiers

2.1. Introduction

A weir may be defined as any regular obstruction in an open channel over which the flow takes

place. It is made of masonry or concrete. It is used for measuring the rate of flow of water in

rivers or streams. More broadly a weir is an overflow structure extending across a stream or a

channel and normal to the direction of the flow. They are normally categorized by their shape as

either sharp-crested or broad-crested. This laboratory experiment focuses on sharp-crested weirs

only. Two different types of weirs will be introduced, The V-notch weir and the rectangular weir

(horizontal weir with end contractions).

2.2. Theory

The theoretical discharge for the rectangular weir is given by

Qtheo = (2/3) (2g)(1/2)

x B x H(3/2) (1)

And for Vee notch is given by:

Qtheo = (8/15) x (2g) (1/2)

x tan(θ/2) x H(5/2) (2)

Where

B = Breadth of rectangular notch

H = Height of flow over notch

θ = Angle of Vee notch

g = Gravitational acceleration

To the contraction of the flow area downstream of the notch, the actual discharge Q is

considerably less and may be expressed as:

Qact = Cd x (2/3) x(2g)(1/2)

x B x H(3/2)

(3)

Qact = Cd x Qth (4)

Where Cd : the coefficient of discharge for the rectangular notch. And expression for Vee

notch:

Qact = Cd x (8/15) x (2g) (1/2)

x tan(θ/2) x H(5/2)

(5)

Qact = Cd x Qth (6)


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Weirs are normally categorized by their shape as either sharp-crested or broad-crested. This

laboratory experiment focuses on sharp-crested weirs only. Two different types of weirs will be

introduced, The V-notch weir and the rectangular weir (horizontal weir with end contractions).

Figure 8 represents the rectangular weir while figure 9 represents a Vee notch weir.

Figure 8: Rectangular Weir

Figure 9: Vee Notch Weir


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2.3. Technical specifications

Dimensions for the following Weirs are given below. Following diagram shows the rectangular

weirs one with broad face and the other one is narrow rectangular weir. Technical data is given

in the table.

Fig 10: broad rectangular weir and narrow rectangular weir

Types Broad rectangular

weir

Narrow rectangular

weir

Breadth 2” 1”

Depth 3” 3”

Table 5 technical data for rectangular weirs

Fig 11: the Vee type Weirs (a angle 90o and b angle 42

o)


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2.4. Experiment: To determine and comment on the coefficient of discharge.

2.4.1. Aim

To determine and comment on the coefficient of discharge for the Vee and Rectangular notches

provided.

2.4.2. Procedure

1. Install the weir plate on the upstream side of the weir carrier and secure it using the thumb

nuts.

2. Position the hook and point gauge, mounted on the instrument carrier, on the side channels

adjacent to the weir plate.

3. Start the pump, and admit water to the channel by opening the flow control valve. Allow the

level to rise until water discharge over the weir plate. Close the flow control valve and allow

the water level to stabilize. Set the height gauge to a datum reading using the top of hook.

4. Admit water to the channel and adjust the flow control valve to obtain heads H increasing in

steps of about 1cm.

5. For each flow rate allow conditions to become steady, measure and record H and take

readings of volume and time using the volumetric tank to determine the flow rate.

6. For ach notch obtain five readings of H and Q.

1.5 Observations and calculations Sample Attached: _________________

Sr # Time

(sec)

Qact

(m3/sec)

H

(mm)

Qtheo

(m3/sec)

Cd

1

2

3

4

5 Table 6: Observation and Calculations

ME-352L Fluid Mechanics Lab II IST-MECH-PWT-EXP03/00

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PELTON WHEEL

TURBINE


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3. Pelton wheel turbine

3.1. Introduction

The unit is designed for training and experimentation. It is used for demonstration purposes

relating to the principle of functioning of a pelton turbine. The orifice of the injection nozzle can

be altered by axial adjustment of the nozzle valve. Load can be placed on the turbine with an

adjustable, mechanical braking device.

The main parts of the pelton turbine are:

1. Nozzle and flow regulating arrangement

2. Runner and buckets

3. Casing

4. Breaking jet

3.2. Description

Fig 12: Pelton wheel turbine


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Pelton wheel turbine consists of following parts:

1. Adjustable breaking device 4. Nozzle inlet 7. Outlet through open

2. Spring balance 5. Turbine housing 8. Pelton wheel

3. Nozzle valve 6. Nozzle adjustment 9. Base plate

3.3. Theory

Hydraulic machines are defined as those machines which convert either hydraulic energy (energy

possessed by water) into mechanical energy or mechanical energy into hydraulic energy.

Turbines are defined as hydraulic machines which convert hydraulic energy into mechanical

energy. hydraulic turbines are of different types according to specification and pelton wheel is

one of the types of hydraulic turbines.

3.3.1. Pelton wheel turbine

The pelton wheel turbine is a tangential flow impulse turbine. The water strikes the bucket along

the tangent of the runner. The energy available at the inlet of the turbine is only kinetic energy.

The pressure at the inlet and outlet is atmospheric. The turbine is used for high heads.

3.3.2. Constructional Details

1. Nozzle and flow regulating arrangement

The amount of water striking the buckets of the runner is controlled by providing a spear in the

nozzle. The spear is a conical needle which is operated either by a hand wheel or automatically

in an axial direction depending upon the size of unit. When the spear is pushed forward into the

nozzle the amount of water striking the runner is reduced. On the other hand if the spear is

pushed back, the amount of water striking the runner increases.

2. Runner with buckets

It consists of a circular disc on the periphery of which a number of buckets evenly spaced are

fixed. The shape of the buckets is of double hemispherical cup or bowl. Each bucket is divided

into two hemispherical parts by a dividing wall which is known as splitter.

3. Casing

The function of the casing is to prevent the splashing of the water and to discharge water to tail

race. It also acts as safe guard against accidents. As pelton wheel is an impulse turbine, the

casing of the pelton wheel does not perform any hydraulic function.


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4. Breaking Jet

When the nozzle is completely closed by moving the spear in the forward direction the amount

of water striking the runner reduces to zero. But the runner due to inertia goes on revolving for a

long time. To stop a nozzle in a short time a small nozzle is provided which directs the jet of

water on the back of buckets. This jet of water is called breaking jet.

5. Working of Pelton wheel turbine

The water from the reservoir flows through the penstocks at the outlet of which a

nozzle is fitted. The nozzle increases the kinetic energy of the water flowing

through the penstock by converting pressure energy into kinetic energy. At the

outlet of the nozzle, the water comes out in the form of jet and strikes on the

splitter, which splits up the jet into two parts. This part of the jet glides over the

inner surfaces and comes out at the outer edge. The buckets are shaped in such a

way that buckets rotates, runner of turbine rotates and thus hydraulic energy of

water is converted into mechanical energy on the runner of turbine which is further

converted into electrical energy in a generator/alternator.


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3.4. Experiment: Pelton Wheel Turbine

3.4.1. Aim To determine the mechanical power produced by the turbine.

3.4.2. Procedure

1. Connect the apparatus with the hydraulic bench.

2. Switch on the hydrau8lic bench pump.

3. Open the valve slowly so that water begins to flow through the turbine.

4. Adjust the flow rate in turbine by nozzle adjuster screw.

5. Load the turbine by turning the adjustment breaking device.

6. Note down the speed of turbine in rpm with the help of tachometer. Note down the Breaking

power F.

Fb = F1 – F2 (7)

7. Now the torque can be calculated by

T = Fb x r (8)

Where r is radius of pulley = 25 mm

8. The mechanical power produced by the turbine can be calculated by

PM = 2πnT / 60 (9)

Where n is speed of the pelton wheel in rpm.

Figure 12: Mechanical Power of a turbine


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3.5. Observations:

No. of obs N

(rpm)

Force F1

(N)

Force F2

(N)

Net force

Fb (N)

Torque T

(Nm)

Power

PM (watt)

1.

2.

3.

Table 7: Observations.

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PIPE FRICTION APPARATUS

ME-352L Fluid Mechanics Lab II IST-MECH-PL-EXP04/00

Page | 27

4. Pipe Friction Apparatus

4.1. Introduction

The unit is used to examine pipe friction losses in laminar and turbulent flow. The pipe section

used has an inside diameter of 4mm and a length of 500mm.The pressure losses are measured in

laminar flow with a water manometer. The static pressure difference is indicated. In turbulent

flow the pressure difference is measured with a water filled manometer. A level tan is provided

to generate the laminar flow. It ensures a constant water inflow pressure on the pipe section at a

constant water level. The level tank is not used to generate turbulent flow. The water is fed

directly from the water main into the pipe section. The flow rate is set by means of valves at each

end of the pipe.

4.2. Theory

The switch from laminar to turbulent flow form occurs when:

Rekr ≈ 2300

Relam< 2300 means laminar flow

Reture > 2300 means turbulent flow

The Reynolds number is calculated from

Re = w x d/v (10)

d = inside diameter of the pipe section [m]

w = flow rate [m/s]

v = viscosity of the medium [m2/s]

For laminar flow Fall

hv = h1 – h2 (11)

h1: static pressure at the entrance to the pipe.

The volume flow V is best measured with a measuring vessel and a stopwatch.

V = Volume/time (12)

The flow rate is produced from:

w = V/A (13)

V = volume flow and A = cross-sectional area of the pipe and A = π x d2 /4 and d = 4mm


Page | 28

The fall hv is set with the drain valve. From the fall the pipe coefficient of friction is calculated λ

as:

λ = (ℎ𝑣 × 𝑑 × 2 × 𝑔)/(𝐿. 𝑤2) (14)

Where l = 500mm pipe section, the value for hv has to be inserted in m

The theoretical pipe coefficient of friction λth is to be compared with the measured value. For

laminar flow:

λth =

64

Re (15)

4.2 For Turbulent Flow

The level tank is not used. For turbulent flow a higher flow rate is required. The water is

therefore fed directly from the hydraulic bench.

Figure 13: Turbulent Flow

hv = h2 – h1 (16)

λth = 0.314

𝑅𝑒

14

(17)


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4.3 Pipe Friction Apparatus

Figure 14: Pipe Friction Appratus

Figure 15: Pipe Friction Appratus.


Page | 30

4.4 Experiment : Pressure loss of Laminar flow and Turbulent Flow

4.4.1 Aim

Pressure loss of laminar flow is to be compared with turbulent flow.

4.4.2 Procedure

For Laminar Flow

Close valve 1 so that water cannot flow through this route. Open valves 2 and 4 and let water

flow through this route. Water will fill up in the level tank open the drain valve so that a constant

level of water is achieved in the level tank. Make this head position with the rubber O-ring

indicator. Turn the valves 5 and 6 so that water flows through the first manometer i.e. the

manometer with water connection at the lower end. Adjust the degassing valve of manometer so

that hv can be achieved. For getting constant head in level tank and laminar flow carefully adjust

the valve of hydraulic bench tank and valve number 7. Measure the flow rate with the help of a

measuring tank and stop watch.

For Turbulent Flow

Fill up the 2nd

manometer with water i.e. the manometer with inlets at the top and ensure that

almost 1/3rd

of both the tubes are filled with water and both are at the same level. If the level of

water in both tubes of manometer is not leveled then remove the pipes from the quick fittings at

valve 5 and 6 and from the manometer. Blow air through them and then attach it again. Ensure

that water level in both tubes of manometer is got leveled and there is no water in the pipes

which are connecting valve 5, 6 with manometer.

Figure 16: Manometers Tube

Now close valve 2, 4 and open valve 1 and reverse the direction of valves 5 and 6. Now start the

hydraulic bench’s pump. Extremely slowly increase the flow through the hydraulic bench valve

and drain valve 7 so that there must be an air column between water coming from pipes through

valve 5 and 6 the water in manometer.


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Figure 17: Pipe friction

Note: If water is filled more than 1/3rd

of the manometer tubes then use the degassing valve to

lower the level of water.Now measure the difference hv and flow rate with help of measuring

thank and stop watch.

Note: Be extremely careful when taking values for turbulent flow. The water level is adjusted

very carefully by using hydraulic bench valve and valve 7. The water in the manometer should

not be getting mixed with water coming from the water through pipes. This condition can only

be achieved by adjusting hydraulic valve and valve 7.


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Figure 18: Wrong alignment

The situation shown in the figure must be avoided. But if water from the pipe goes in the

manometer then switch off the pump. Open the degassing valve to drain water from manometer

and fill it again as mentioned earlier. Also blow air from both the pipes. Pipes should be clean

and there should be no water droplets in it.

4.4.3 Observations No.

of obs

hv

(mm)

T

(s)

v

(l)

V

(l/s)

W

(m/s) Re λ λth

1.

2.

3.

4.

5.

6.

Table 8: Observations for Pipe Friction Apparatus.

Page | 33

MODEL: ME-FM-3777

SERIES AND PARALLEL

PUMP TEST BENCH

ME-352L Fluid Mechanics Lab II IST-MECH-PTB-EXP05/01

Page | 34

5. Series and Parallel Pump

5.1. Introduction

Pumps are used in almost all aspects of industry and engineering from feeds to reactors and

distillation columns in chemical engineering to pumping storm water in civil and environmental.

They are an integral part of engineering and an understanding of how they work is important.

Centrifugal pump is one of the most widely used pumps for transferring liquids. This is for a

number of reasons. Centrifugal pumps are very quiet in comparison to other pumps. They have a

relatively low operating and maintenance costs. Centrifugal pumps take up little floor space and

create a uniform and non-pulsating flow.

The Test Rig is specially designed to demonstrate to students the operating characteristics of

centrifugal pump in series or parallel. This training unit operates in close loop. This equipment

will explore the relationship between pressure head and flow rate of a single pump and of two

identical pumps that are run in series or in parallel. When identical pumps are run in series, the

pressure head is doubled but the flow rate remains the same. When pumps are run in parallel the

flow is increased but the pressure head produced is approximately the same as a single pump.

This equipment also allows the study of efficiency of a pump. The energy in this experiment is

put through two transformations. First, the electrical energy, which is the energy put into the

system, is transferred to mechanical energy, which is the energy required to move the shaft and

impeller. Second, the mechanical energy is transferred into energy of the fluid. This is

accomplished through the pump rotation, which transfers the velocity energy of the water to

pressure energy. The overall efficiency is the product of the mechanical (shaft) efficiency and the

thermodynamics efficiency.


Page | 35

Figure 19: Process Diagram

5.2. Specifications

Before operation, students must familiarize themselves with the unit. Please refer to Figure 1 to

understand the process. The unit consists of the followings:

a) Pumps Two units of Horizontal Single Stage Centrifugal Pump (P1) and (P2)

b) Circulation Tank A stainless steel water tank is provided to supply water to P1 and P2.

c) Flow rate and pump head indicators.

d) Process piping The process piping is made of industrial PVC pipes. Valves used are ball valves.

e) ON/OFF switch Two On/Off switches allows the selection of system operates either with 1 pump or 2 pumps

(series/parallel).

Flow indicator: Indicated value is in Liters Per Minute (LPM).

Pressure Indicator: Indicated value is in bar.

Pressure Gauge 1 (PT1) -1 to 3 bar

Pressure Gauge 2 (PT2) 0 to 6 bar

Pressure Gauge 3 (PT3) 0 to 16 bar

Table 9: Pressure Ranges


Page | 36

5.3. General requirements

Electrical : 240 VAC, 1-phase, 50Hz

Water : Laboratory main supply

5.4. Theory

Pumps are devices that transfer mechanical energy from a prime mover into fluid energy to

produce the flow of liquids. There are two broad classifications of pumps: positive displacement

and dynamic.

5.5 Dynamic Pumps

Dynamic pumps add energy to the fluid by the action of rotating blade, which increases the

velocity of the fluid. Figure 2 shows the construction features of a centrifugal pump, the most

commonly used type of dynamic pumps.

Figure 20: Construction Features Of a Centrifugal Pump.

5.5.1 Horizontal Single Stage Centrifugal Pump

Centrifugal pumps have two major components:

1. The impeller consists of a number of curved blades (also called vanes) attached in a

regular pattern to one side of a circular hub plate that is connected to the rotating

driveshaft.

2. The housing (also called casing) is a stationary shell that enclosed the impeller and

supports the rotating drive shaft via a bearing.

A centrifugal pump operates as follows. When the prime mover rotates the driveshaft, the

impeller fluid is drawn in axially through the center opening (called the eye) of the housing. The

fluid then makes a 900 turn and flows radially outward. As energy is added to the fluid by the

rotating blades (centrifugal action and actual blade force), the pressure and velocity increase until

the fluid reaches the outer tip of the impeller. The fluid then enters the volute-shaped housing


Page | 37

whose increased flow area causes the velocity to decrease. This action results in a decrease in

kinetic energy and an accompanying increase in pressure.

The volute-shaped housing also provides a continuous increase in flow area in the direction of

flow to produce a uniform velocity as the fluid travels around the outer portion of housing and

discharge opening. Although centrifugal pumps provide smooth and continuous flow, their flow

rate output (also called discharge) is reducing as the external resistance is increase. In fact, by

closing a system valve (thereby creating theoretically infinite external system resistance) even

while the pump is running at design speed, it is possible to stop pump output flow completely. In

such a case, no harm occurs to the pump unless this no-flow condition occurs over extended

period with resulting excessive fluid temperature build up. Thus pressure relief valves are not

needed. The tips of the impeller blade merely shear through the liquid, and the rotational speed

maintains a fluid pressure corresponding to the centrifugal force established. Figure 3 shows the

cutaway of a centrifugal pump.

Figure 21: The Cutaway of a Centrifugal Pump.

5.5.2 Pump Head versus Flow rate Curves for Centrifugal Pumps

Figure 20 shows pump head versus flow rate curves for a centrifugal pump. The solid curve is

for water, whereas the dashed curve is for a more viscous fluid such as oil. Most published

performance curves for centrifugal pumps are for pumping water. Notice from Figure 4 that

using a fluid having a higher viscosity than water results in a smaller flow rate at a given pump

head. If the fluid has a viscosity greater than 300 times that of water, the performance of a

centrifugal pump deteriorates enough that a positive displacement pump is usually

recommended.


Page | 38

Figure 22: Pump Performance Curve

The maximum head produced by a centrifugal pump is called pump shutoff head because an

external system valve is closed and there is no flow. Notice from Figure 4 that as the external

system resistance decrease (which occurs when a system valve is opened more), the flow rate

increases at the expense of reduced pump head. Because the output flow rate changes

significantly with external system resistance, centrifugal pumps are rarely used in fluid power

systems. Zero pump head exists if the pump discharge port were opened to the atmosphere, such

as when filling nearby open tank with water. The open tank represents essentially zero resistance

to flow for the pump. Figure 20 shows why centrifugal pumps are desirable for pumping stations

used for delivery water to homes and factories. The demand for water may go to near zero during

the evening and reach a peak during the daytime, but a centrifugal pump can readily handle these

large changes in water demand. Since there is a great deal of clearance between the impeller and

housing, centrifugal pumps are not self-priming, unlike positive displacement pumps. Thus if a

liquid being pumped from a reservoir located below a centrifugal pump, priming is required.

Priming is the prefilling of the pump housing and inlet pipe with the liquid so that the pump can

initially draw the liquid. Priming is required because there is too much clearance between the

pump inlet and outlet ports to seal against atmospheric pressure. Thus the displacement of a

centrifugal pump is not positive where the same volume of liquid would be delivered per

revolution of the driveshaft.

The lack of positive internal seal against leakage means that the centrifugal pump is not forced to

produce flow when there is a very large system resistance to flow. As system resistance

decreases, less fluid at the discharge port slips back into the clearance spaces between the

impeller and housing, resulting in an increase in flow. Slippage occurs because the fluid follows

the path of least resistance.


Page | 39

5.5.3 Centrifugal Pump Connected in Parallel

If a single pump does not provide enough flow rates for a given application, connecting two

pumps in parallel, as shown in Figure 23, can rectify the problem. The effective two-pump

performance curve is obtained by adding the flow rates of each pump at the same head. As

shown, when two pumps are connected in parallel, the operating points shift from A to B,

providing not only increased flow rate as required but also greater head. Figure 23 shows the

characteristics of two identical pumps, but the pumps do not have to be the same.

Figure23: Centrifugal Pumps in parallel

5.5.4 Centrifugal Pump Connected in Series

On the other hand, if a single pump does not provide enough head for a given application, two

pumps connected in series, as shown in Figure 24 , can be a remedy. The effective two-pump

performance curve is obtained by adding the head of each pump at the same flowrate. The

operating point shifts from A to B, thereby providing not only increased head as required but

also greater flow. Figure 6 shows the characteristics of two identical pumps, but the pumps do

not have to be the same.


Page | 40

Figure 24: Two centrifugal pumps connected in series

5.5.5 Impeller Types

An impeller is a rotating component of a centrifugal pump which transfers energy from the

motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the

centre of rotation. The velocity achieved by the impeller transfers into pressure when the

outward movement of the fluid is confined by the pump casing. Impellers are usually short

cylinders with an open inlet (called an eye) to accept incoming fluid, vanes to push the fluid

radially, and a splined, keyed or threaded bore to accept a driveshaft.

5.5.6 Backward-curved Blades

Backward-curved blades use blades that curve against the direction of the pump impeller's

rotation. Centrifugal pumps with backward-curved blades yield higher efficiency compare to the

forward-curved blades because the fluid flows into and out of the blade passages with the least

amount of turning. Sometimes the blades are air foil shaped, yielding similar performance but

even higher efficiency. The pressure rise is intermediate between radial and forward-curved

blades. Backward-curved pumps are preferred for applications where one needs to provide

volume flow rate and pressure rise within a narrow range of values. Backward curved pumps can

have a high range of specific speeds but are most often used for medium specific speed

applications-- high pressure, medium flow applications.

5.5.7 Forward-curved Blades

Forward curved blades, which curve toward the direction of pump impeller’s rotation.

Centrifugal pumps with forward-curved blades produce pressure rise that is nearly constant,

albeit lower than that of radial and backward-curved blades, over a wide range of volume flow


Page | 41

rates. Centrifugal pumps with forward-curved blades generally have a lower maximum

efficiency. Forward-curved pumps are for high flow, low pressure applications.

Formula for Calculation of Variables

Overall Efficiency

Power (fluid)

Gravitational

Acceleration

Volumetric flow rate

Pump Head

Pressure unit [P1,P2] is Pascal

Unit conversion : 1 bar = 100000 Pascal

Water Density

Table 10: Formula for calculations

Figure 24: Forward and backward-curved blades


Page | 42

5.6 General start-up procedures

Before conducting any experiment, it is necessary to do the following checking to avoid any

misused and malfunction of equipment.

1. The circulation tank is filled with water.

2. Make sure V5 is in fully close position.

3. Switch on the main power supply.

4. Check for the following valve position.

5. Turn on the pumps and slowly open V4 until maximum flow rate is achieved. Follow the

experiment procedures to determine the desired flow rate.

6. Close V4 accordingly to get desired flow rate.

7. Note down flow rate and pressures.

5.7 General shut-down procedures

1. Turn off the pump.

2. Make sure valve V4 is in fully close position.

3. Turn off the pump switches on the panel.

4. Switch off the main power supply.

Note: For each experiment refill the water tank and after experiment empty it.

Pump Operation Running Pump Fully Open Valve Fully Close Valve

Series Both Pump, P1 & P2 V2 V1, V3

Parallel Both Pump, P1 & P2 V1, V3 V2

Table 10: Start up Procedures.


Page | 43

5.8 Experiment: characteristics of pump-in-series operation

5.8.1 Aim

To study the characteristics of pump-in-series operation with variable flow rate.

5.8.2 Equipment Set Up

Fully Close

Valve

Fully Open

Valve

Variable

Parameter Pump ON

V1 & V3 V2 V4 Both Pump


Page | 44

5.9 Experiment 2

5.9.1 Aim

To study the characteristics of pump-in-parallel operation with variable flow rate.

5.9.2 Equipment Set Up

5.9.3 Procedures

1) Follow the basic procedure as written in previous section.

2) Ensure that all setting follows the equipment set up.

3) Test the pump characteristics by changing the flow rate from V4.

5.9.4 Assignment

1) Plot pressure difference pump head (m) vs. flow rate for condition.

2) Plot efficiency vs. flow rate for condition.

5.10 SAFETY PRECAUTION 1. Never operate the pumps when there is no liquid in the pipeline. It will cause serious damage

to the pumps. (Water Level must be checked from the manometer at the front of tank.)

2. Do not operate pump above and below its limit.

Fully Close

Valve

Fully Open

Valve

Variable

Parameter Pump ON

V2 V1 & V3 V4 Both Pump

Page | 45

Axial Flow Fan

ME-352L Fluid Mechanics Lab II IST-MECH-AFF-EXP06/00

Page | 46

6 Axial flow Fan

6.1 Control unit

A control unit is present to control the rpm of the fan manually. It is connected with a number of

sensors (differential pressure sensor at orifice and fan, temperature sensor, rpm sensor). It also

indicates the voltage and current supplied to the fan.

6.1.1 Main air flow tube

The main air flow tube consists of following part.

6.1.2 Orifice

An orifice is situated at the inlet of the main air flow tube which is useful for accelerating the air

flow. It is also useful for the flow measurement in the tube.

6.1.3 Flow regulator

After the orifice, a flow regulator is present which has a shape similar to that of honeycomb. It is

used as a flow regulator to convert the turbulent flow to comparatively laminar flow.

6.1.4 Axial fan

Axial fan is used to produce the required suction to draw the air into the tube and then blows the

air away to the outlet of the pipe.

6.1.5 Damper

At the outlet, a damper is situated which can be moved inward or outward to produce or reduce

the air cushion at the outlet.

6.2 Theory

Most manufacturing plants use fans and blowers for ventilation and for industrial processes that

need an air flow. Fan systems are essential to keep manufacturing processes working, and consist

of a fan, an electric motor, a drive system, ducts or piping, flow control devices, and air

conditioning equipment (filters, cooling coils, heat exchangers, etc.).

Fans, blowers and compressors are differentiated by the method used to move the air, and by the

system pressure they must operate against. The American Society of Mechanical Engineers

(ASME) uses the specific ratio, which is the ratio of the discharge pressure over the suction


Page | 47

pressure, to define fans, blowers and compressors (see Table 1).

6.3 Types of fans

There exist two main fan types. Centrifugal fans used a rotating impeller to move the air stream.

Axial fans move the air stream along the axis of the fan.

6.3.1 Centrifugal fans

Centrifugal fans (Figure 6) increase the speed of an air stream with a rotating impeller. The

speed increases as the reaches the ends of the blades and is then converted to pressure. These

fans are able to produce high pressures, which makes them suitable for harsh operating

conditions, such as systems with high temperatures, moist or dirty air streams, and material

handling.

6.3.2 Axial fans

Axial fans move an air stream along the axis of the fan. The way these fans work can be

compared to a propeller on an airplane: the fan blades generate an aerodynamic lift that

pressurizes the air. They are popular with industry because they are inexpensive, compact and

light. The main types of axial flow fans (propeller, tube-axial and vane-axial) are summarized in


Page | 48

Table below

6.4 Characteristic curve for axial fan

The relation between the differential pressure and the flow rate is inverse proportionality for

axial fan. As the differential pressure across the fan rises, the flow rate is reduced.

The trend is shown in fig below.

Figure 25: Characteristic Curve


Page | 49

6.5 Experiment: Relation between differential pressure across fan and volume

flow rate

6.5.1 Aim

To identify the relation between differential pressure across fan and volume flow rate.

6.5.2 Procedure

Close the damper tightly.

Turn on the control unit and start increasing the rpm.

Note the readings on the control unit indicator when rpm is approximately near

10,000.

Then open the damper a little bit and note down the readings again.

Note down 5 to 6 readings in the same way.

6.5.3 Observations and Calculations

Sr.

No

Differentia

l pressure

across

orifice

( dPo )

Differenti

al

pressure

across fan

( dPf )

Voltage

( V )

Current

( I )

RPM Temperat

ure

T

Nm-2

Nm-2

V A Rev/min C

1

2

3

4

5

6 Table 11: Observations

The flow rate can be calculate by

(18)


Page | 50

η = (work done on air per second) / (power supplied to fan)

𝜂 =

𝑑𝑝𝑓×𝑄

𝑉×𝐼 (19)

Where

Q = volume flow rate at inlet

M= mass flow rate at inlet = mass flow rate at outlet

M = Q*ρ

A2 = Area of orifice = ∏r2

= 0.00441 m2

A1 = Area of pipe = ∏R2 = 0.01038 m

2

dp = differential pressure across orifice

Cd = Discharge co-efficient = 0.6

ρ = Density of air = 1.18 kg/m3

Sr.

No

Volume

flow rate

Q

Mass

flow rate

M

Power

provided to

fan of Fan

Pf

Power

transferred

to air

Pa

Efficiency of

fan

ηf

m3/s Kg/sec Watt Watt

1

2

3

4

5

6

Table 12: Calculations

Documents

Fluid Mechanics 2 Lab Manual