INSTRUCTION MANUAL
F1-18
ENERGY LOSSES IN PIPES
F1-18
ISSUE 3
SEPTEMBER 2001
ARMFIELD LIMITED
OPERATING INSTRUCTIONS AND EXPERIMENTS
F1-18
SAFETY IN THE USE OF EQUIPMENT SUPPLIED BY ARMFIELD
1
INTRODUCTION
2
DESCRIPTION
3
COMMISSIONING
4
ROUTINE MAINTENANCE
6
NOMENCLATURE
7
EXPERIMENTAL PROCEDURE
9
F1-18 Energy Losses In Pipes
SAFETY IN THE USE OF EQUIPMENT SUPPLIED BY ARMFIELD
Before proceeding to operate the equipment described in this text we wish to alert you
to potential hazards so that they may be avoided.
Although designed for safe operation, any laboratory equipment may involve processes
or procedures which are potentially hazardous. The major potential hazards associated
with this particular equipment are listed below.
• INJURY THROUGH MISUSE
• INJURY FROM ELECTRIC SHOCK
• DAMAGE TO CLOTHING
• RISK OF INFECTION DUE TO LACK OF CLEANLINESS
• POISONING FROM TOXIC MATERIALS (EG. MERCURY)
Accidents can be avoided provided that equipment is regularly maintained and staff
and students are made aware of potential hazards list of general safety rules is included
in the F1 Product Manual to assist staff and students in this regard. The list is not
intended to be fully comprehensive but for guidance only.
Please refer to the notes in the F1 Product Manual regarding the Control of Substances
Hazardous to Health Regulations,
The F1-10 Service Bench operates from a mains voltage electrical supply. The
equipment is designed and manufactured in accordance with appropriate regulations
relating to the use of electricity. Similarly, it is assumed that regulations applying to the
operation of electrical equipment are observed by the end user.
However, to give increased operator protection, Armfield Ltd have incorporated a
Residual Current Device (RCD, alternatively called an Earth Leakage Circuit Breaker
or ELCB) as an integral part of the service bench. If through misuse or accident the
equipment becomes electrically dangerous, an RCD will switch off the electrical supply
and reduce the severity of any electric shock received by an operator to a level which,
under normal circumstances, will not cause injury to that person.
Check that the RCD is operating correctly by pressing the TEST button. The circuit
breaker MUST trip when the button is pressed. Failure to trip means that the operator is
not protected and the equipment must be checked and repaired by a competent
electrician before it is used.
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F1-18 Energy Losses In Pipes
INTRODUCTION
Fluid mechanics has developed as an analytical discipline from the application of the
classical laws of statics, dynamics and thermodynamics, to situations in which fluids
can be treated as continuous media. The particular laws involved are those of the
conservation of mass, energy and momentum and, in each application, these laws may
be simplified in an attempt to describe quantitatively the behaviour of the fluid.
The hydraulics bench service module, F1-10, provides the necessary facilities to
support a comprehensive range of hydraulic models each of which is designed to
demonstrate a particular aspect of hydraulic theory.
The specific hydraulic model that we are concerned with for this experiment is the Pipe
Friction Test Rig, F1-18. This consists of a test pipe which may be fed water at high or
low flow rates. Two manometers, a water over mercury manometer and a pressurised
water manometer can then be used to measure the head losses in the pipe. A full
description of the apparatus is given later in these texts.
2
F1-18 Energy Losses In Pipes
DESCRIPTION
Inlet Pipe to
Constant
Head Tank
Inlet Pipe
to Test
Section
Air Bleed Screws
Pressure Tapping (H.P.)
Test Section (I/D 3mm
Air Pump
Water Over Mercury
Manometer with Scale
Pressurised Water
Manometer with Scale
Pipe Clips
Constant Head
Tank
Air Inlet/Outlet
Valve
Pressure Tapping (L.P.)
Flexible Outlet
Pipe from
Head Tank
Overflow
Flow Control Valve
Adjustable Feet
The accessory is designed to be positioned on the side channels of the hydraulics bench
top channel.
There are two methods of supplying water to the test pipe. For higher flow rates the
inlet pipe is connected directly to the bench supply. For lower flow rates, the inlet pipe
is connected to the outlet at the base of the constant head tank and the inlet to the tank is
connected to the bench supply.
The test section of pipe is mounted vertically on the rig and is instrumented using two
manometers. A water over mercury manometer is used to measure large pressure
differentials and a pressurised water manometer is used to measure small pressure
differentials. When not in use a manometer may be isolated using Hoffman clips.
Flow through the test section is regulated using a flow control valve. In use this valve
should face the volumetric tank. A short length of flexible piping attached to the valve
will prevent splashing.
3
F1-18 Energy Losses In Pipes
COMMISSIONING
The apparatus is supplied fully assembled and ready for connection to the F1-10
Hydraulics Bench. The mercury manometer fitted to the column must be primed with
mercury before the apparatus can be used. The apparatus can be prepared for use as
follows:Before filling the apparatus with water remove the flexible connection from the tapping
at the base of each manometer tube and place a drop of wetting agent into the tube.
Replace each flexible tube and ensure that the clip is secured.
Locate the apparatus over the moulded channel in the top of the bench.
Connect the flexible inlet tube from the top of the test pipe to the outlet fitting in the
bed of the moulded channel.
Place the free end of the flexible tube from the overflow on the top reservoir (tube exits
from the side of the supporting column near the base) through the overflow in the side
of the volumetric tank (water overflowing from the constant head arrangement should
return directly to the sump and not into the volumetric tank).
Open the discharge flow control valve at the bottom of the test pipe.
Close the bench flow control valve, start the service pump then open the bench flow
control valve slightly.
Allow water to flow through the test pipe until all air is dispelled.
Close off the flexible connections to the mercury manometer (fitted with knurled screws
at the top) using the tubing clips supplied and allow water to flow through the water
manometer until all air bubbles have dispersed.
Open the connections to the mercury manometer and close off the flexible connections
to the water manometer. Open the knurled screw at the top of each manometer tube
briefly to allow the tube to fill with water.
When the apparatus is fully primed close the discharge flow control valve at the bottom
of the test pipe then close the bench flow control valve and switch off the service pump.
Remove the knurled screws from the top of each tube on the mercury manometer then
carefully pour approximately 0.4 kg of clean mercury (not supplied) into one of the
tubes using a small funnel (not supplied) until the level of the mercury coincides with
250 mm on the manometer scale. Water will be displaced as the mercury enters
ensuring that no air is trapped in the manometer tube. When the mercury is at the
correct level replace the two knurled screws and tighten them.
Place the flexible tube attached to the exit from the test pipe in the clip on the side of
the support column. Position the end of the flexible tube so that water exiting the tube
can be collected using a measuring cylinder. For accurate results at low flowrate, the
position of the flexible tube should not be moved while taking readings.
4
F1-18 Energy Losses In Pipes
Note: Low flowrates through the test pipe can be generated using the head tank at the
top of the support column. The flexible inlet tube on the test pipe is connected to
the tapping at the base of the head tank and the inlet tube to the head tank is
connected to the outlet fitting in the bed of the moulded channel.
The flow of water to the head tank should be adjusted using the bench flow control
valve so that water just flows from the overflow. If the bench flow control valve is
opened too far then water will spill from the top of the head tank.
Note: When using the mercury manometer to measure head loss in excess of the range
on the water manometer it will be necessary to close the flexible tubing to the
water manometer using the tubing clips supplied.
The F1-18 Energy Loss In Pipes apparatus is ready for use.
5
F1-18 Energy Losses In Pipes
ROUTINE MAINTENANCE
Little maintenance is required but it is important to drain all water from the constant
head tank and all pipework when not in use. It is not necessary to drain the mercury
from the mercury manometer or the water trapped above the mercury columns.
The apparatus should be stored where protected from damage.
6
F1-18 Energy Losses In Pipes
NOMENCLATURE
Column
Heading
Units
Nom.
Type
Description
Length of
Test Pipe
m
L
Given
Length of pipe test section. The test pipe
length is measured in mm. Convert to
metres for the calculation.
Diameter of
Test Pipe
m
d
Given
Diameter of pipe test section The test
pipe diameter is measured in mm.
Convert to metres for the calculation.
.
Volume
Collected
m3
V
Measured
Volume of water collected in a known
time. The volume is measured in ml.
Convert to cubic metres for the
calculation. (divide reading by
1,000,000)
Time to
Collect
s
t
Measured
Time taken to collect the known
volume of water, V.
Temp of
Water
°C
Measured
The temperature of the water collected.
Kinematic
Viscosity
m2/s
ν
Measured
See Table
Manometer
m
h1
Measured
Head at inlet to test section of the pipe.
The head is measured in mm. Convert to
metres for the calculation.
Manometer
m
h2
Measured
Head at outlet to test section of the pipe.
The head is measured in mm. Convert to
metres for the calculation.
Head Loss
m
h1 - h2
Calculated
Head loss over the test section of the
pipe.
Flow Rate
m3/s
Qt
Calculated
Velocity
m/s
v
Calculated
7
Qt =
Volume Collected
v
=
t
Time to Collect
Fluid velocity through the pipe
Flow Rate
v=
Area of Pipe
F1-18 Energy Losses In Pipes
2gd
Lv 2
Friction
Factor
f
Calculated
f = ∆h
Reynolds
Number
ln f
Re
Calculated
vd
ν
Natural log of friction factor, f, to show
relationship between f and Re
Calculated
Re =
ln Re
Calculated
Natural log of Reynolds Number, Re, to
show relationship between f and Re
ln h
Calculated
Natural log of head loss, h, to show
relationship between h and v
ln v
Calculated
Natural log of velocity, v, to show
relationship between h and v
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F1-18 Energy Losses In Pipes
EXPERIMENTAL PROCEDURE
Objective
To investigate the head loss due to friction in the flow of water through a pipe and to
determine the associated friction factor. Both variables are to be determined over a
range of flow rates and their characteristics identified for both laminar and turbulent
flows.
Method
By measurement of the pressure difference between two fixed points in a long (length =
many diameters) straight tube of circular cross-section for steady flows. The range of
flow rates will cover both laminar and turbulent flow regimes.
Equipment
In order to complete the demonstration we need a number of pieces of equipment.
•
•
•
•
•
•
The F1-10 Hydraulics Bench which allows us to measure flow by timed volume
collection.
The F1-18 Pipe Friction Apparatus.
A stopwatch to allow us to determine the flow rate of water (not supplied).
A thermometer (not supplied).
A spirit level for setting up the equipment
A measuring cylinder for measuring very low flow rates (supplied with hydraulics
bench)
Technical Data
The following dimensions from the equipment are used in the appropriate calculations.
If required these values may be checked as part of the experimental procedure and
replaced with your own measurements.
Length of test pipe
Diameter of test pipe
L = 0.500
d = 0.003
m
m
Theory
A basic momentum analysis of fully developed flow in a straight tube of uniform crosssection shows that the pressure difference (p 1 − p 2 ) between two points in the tube is
due to the effects of viscosity (fluid friction). The head-loss ∆h is directly proportional
to the pressure difference (loss) and is given by
∆h =
(p 1 − p 2 )
ρg
and the friction factor, f, is related to the head-loss by the equation
∆h =
fLv 2
2gd
9
F1-18 Energy Losses In Pipes
where d is the pipe diameter and, in this experiment, ∆h is measured directly by a
manometer which connects to two pressure tappings a distance L apart; v is the mean
velocity given in terms of the volume flow rate Qt by
v=
4Q t
πd 2
The theoretical result for laminar flow is
f=
64
Re
where Re = Reynolds number and is given by
Re =
vd
ν
and ν is the kinematic viscosity.
For turbulent flow in a smooth pipe, a well known curve fit to experimental data is
given by
f = 0.316 Re −0.25
Procedure - Equipment Set Up
Mount the test rig on the hydraulic bench and, with a spirit level, adjust the feet to
ensure that base plate is horizontal and, hence, the manometers are vertical.
Check with a demonstrator that the mercury (Hg) manometer is correctly filled; this
should not be attempted by students because Hg is a hazardous substance. Attach a
Hoffman clamp to each of the two manometer connecting tubes and close them off.
Setting-up for high flow rates
The test rig outlet tube must be held by a clamp to ensure that the outflow point is
firmly fixed. This should be above the bench collection tank and should allow enough
space for insertion of the measuring cylinder.
Join the test rig inlet pipe to the hydraulic bench flow connector with the pump turned
off.
Close the bench gate-valve, open the test rig flow control valve fully and start the
pump. Now open the gate valve progressively and run the system until all air is purged.
Open the Hoffman clamps and purge any air from the two bleed points at the top of the
Hg manometer.
Setting up for low flow rates (using the header tank)
10
F1-18 Energy Losses In Pipes
Attach a Hoffman clamp to each of the two manometer connecting tubes and close them
off.
With the system fully purged of air, close the bench valve, stop the pump, close the
outflow valve and remove Hoffman clamps from the water manometer connections.
Disconnect test section supply tube and hold high to keep it liquid filled.
Connect bench supply tube to header tank inflow, run pump and open bench valve to
allow flow. When outflow occurs from header tank snap connector, attach test section
supply tube to it, ensuring no air entrapped.
When outflow occurs from header tank overflow, fully open the outflow control valve.
Slowly open air vents at top of water manometer and allow air to enter until manometer
levels reach convenient height, then close air vent. If required, further control of levels
can be achieved by use of hand-pump to raise manometer air pressure.
Procedure - Taking a Set of Results
Running high flow rate tests
Apply a Hoffman clamp to each of the water manometer connection tubes (essential to
prevent a flow path parallel to the test section).
Close the test rig flow control valve and take a zero flow reading from the Hg
manometer, (may not be zero because of contamination of Hg and/or tube wall).
With the flow control valve fully open, measure the head loss hHg shown by the
manometer.
Determine the flow rate by timed collection and measure the temperature of the
collected fluid. The Kinematic Viscosity of Water at Atmospheric Pressure can then be
determined from the table provided in this manual.
Repeat this procedure to give at least nine flow rates; the lowest to give hHg = 30mm
Hg, approximately.
Running low flow rate tests
Repeat procedure given above but using water manometer throughout.
With the flow control valve fully open, measure the head loss h shown by the
manometer.
Determine the flow rate by timed collection and measure the temperature of the
collected fluid. The Kinematic Viscosity of Water at Atmospheric Pressure can then be
determined from the table provided in this manual.
Obtain data for at least eight flow rates, the lowest to give h = 30mm, approximately.
Plot graphs of:
11
F1-18 Energy Losses In Pipes
ln (friction factor) vs ln (Reynold’s no.)
and
ln (head loss) vs ln (velocity)
Kinematic Viscosity of Water at Atmospheric Pressure
Temperature
(degrees C)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Kinematic
Viscosity
ν
6
(10 x m2/s)
1.793
1.732
1.674
1.619
1.568
1.520
1.474
1.429
1.386
1.346
1.307
1.270
1.235
1.201
1.169
1.138
1.108
1.080
1.053
1.027
1.002
0.978
0.955
0.933
0.911
Temperature
(degrees C)
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
45
50
55
60
65
70
75
80
85
Eg. At 20°C the kinematic viscosity of water is 1.002 x 10-6m2/s.
12
Kinematic
Viscosity
ν
6
(10 x m2/s)
0.893
0.873
0.854
0.836
0.818
0.802
0.785
0.769
0.753
0.738
0.724
0.711
0.697
0.684
0.671
0.658
0.602
0.554
0.511
0.476
0.443
0.413
0.386
0.363
0.342
F1-18 Energy Losses In Pipes
Recording your Results
Tabulate your results as follows:
Test
Pipe
Length
L
(m)
Test
Pipe
Diam.
d
(m)
Volume
V
(m³)
Time
To
Collect
t
(sec)
Temp
of
Water
(°C)
Kin.
Visc.
Man.
Man.
Head
Loss
Flow
Rate
Vel.
ν
(m²/s)
h1
(m)
h2
(m)
∆h
(m)
Qt
(m³/s)
v
(m/s)
Friction
Factor
Reynolds
Number
In
f
f
Re
Application of Theory
Identify the laminar and turbulent flow regimes. What is the critical Reynolds Number?
Assuming a relationship of the form f = K Re n calculate these values from the graphs
you have plotted and compare these with the accepted values shown in the theory
section.
What is the cumulative effect of experimental errors on the values of K and n?
What is the dependence of head loss upon flow rate in the laminar and turbulent regions
of flow?
What is the significance of changes in temperature to the head loss?
13
In
Re
In
h
In
V