UNIVERSITY OF NAIROBI
SCHOOL OF ENGINEERING
DEPARTMENT OF MECHANICAL AND MANUFACTURING
ENGINEERING
FINAL YEAR PROJECT REPORT
[FME 561 &562]
REVIEW DESIGN OF UNIVERSITY OF NAIROBI MAIN CAMPUS
BOREHOLE WATER SUPPLY SYSTEM
PROJECT CODE: GON O2/2012
SUPERVISOR: ENG. G.O NYANGASI
COMPILED BY:
NJUGI DAVID MAINA
MBURU PETER NJOROGE
F18/1875/2007
F18/21299/2006
MAY 2012
This project report is submitted in partial fulfillment of the requirement for the award of the
degree of Bachelor of Science in Mechanical Engineering.
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ABSTRACT
The objective of the project was to review the design of University of Nairobi main campus
borehole water supply system. His was accomplished by collecting data on the current
discharge of the pump from the meter. The discharge was found to be 10 m3/hr. with the
pump operating for 22 hours a day. This results to 220 m3/hr. per day. The pump can
produce a discharge of 16m3/hr. and produce a head of 225 MoW.
From the manufacturer’s pump characteristic curve it was found that at a discharge of
10m3/hr the head the pump can overcome is 280 MoW. The total head across the pipeline
system was calculated and found to be 211.83 MoW. Therefore the pump can overcome the
total head in the system.
The current water demand was found to be 225 m3/day. Therefore the water supply falls
short of the demand by 5 m3/day. It was also found that the main reservoir has a capacity of
16m3.
The main challenges that the current design faces are among others, the fact that it does not
meet the demand, that the main reservoir is too small and because of this the pump is made
to run for long hours which leads to accelerated wear and frequent failure and that the pump
is operating at below its design output.
The proposed design is meant to address the shortcomings of the current system. It entails
putting up a larger reservoir of approximately 200,000 litres at ground level and using a
booster pump to supply the current main reservoir which then distributes to the other
reservoirs.
Recommendations for further study of the design were proposed.
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ACKNOWLEGEMENT
We would lie to express our sincere gratitude to all those who helped in whatever way to the
completion of this project. First among them is Eng. G. O. Nyangasi, our supervisor who
tirelessly guided us through the project and for his invaluable advice and suggestion. We
would also like to thank Mr. Edwin from the maintenance department for his selfless service
when we needed him. We also appreciate our parents for their encouragement and support
throughout our undergraduate program. Last but not the least we would like to appreciate
Mechanical Engineering class of 2012 for their endless support and commitment.
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NOMENCLATURE
v=Velocity at periphery of impeller
g = acceleration due to gravity m/s2
Hs = total static head to be overcome;
Hf = pressure head loss due to fluid friction.
P= the wetted perimeter
τo = the shear stress
θ = angle
C= Chezy constant
f= friction factor
λ= coefficient of friction
d= diameter of pipe
ρ= density of water in Kg/m3
Q = flow rate in m3/s
H = total head in MoW
k= surface roughness of pipe
MoW= meters of water
υ=kinematic viscosity of water
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TABLE OF CONTENTS
Title ............................................................................................................................
Abstract ........................................................................................................................
Acknowledgement ........................................................................................................
Nomenclature ...............................................................................................................
Table of Contents ........................................................................................................
CHAPTER I.0: INTRODUCTION
1.1 The history of The University of Nairobi ................................................................
1.2 Water as a resource ................................................................................................
1.3 Water supply in Kenya ...........................................................................................
1.4 Water supply systems .............................................................................................
CHAPTER 2.0: LITERATURE REVIEW
2.1 Important definitions and terms ..............................................................................
2.1.1 Pumps .................................................................................................................
2.1.1.1 Well pumps ......................................................................................................
2.1.1.2 Deep well pumps .............................................................................................
2.1.1.3 Centrifugal pumps ...........................................................................................
2.1.2 Total pressure head .............................................................................................
2.1.2.1 Total static head (Hs) ........................................................................................
2.1.2.2 The friction head (Hf)........................................................................................
2.1.3 Suction design .....................................................................................................
2.1.3.1 Positive static suction head arrangement (NPSH) ..............................................
2.1.3.2 Negative static suction head (NSSH).................................................................
2.1.4 Pumping power....................................................................................................
2.1.4.1 Water Horsepower ............................................................................................
2.1.4.2 Pump shaft power .............................................................................................
2.1.5 Electric motors ....................................................................................................
2.1.5.1 Electric motor power requirements ...................................................................
CHAPTER 3.0: OBJECTIVE STATEMENT
3.1Existing University of Nairobi borehole water supply system ..................................
3.1.1 Borehole ..............................................................................................................
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3.1.2 Pump ...................................................................................................................
3.1.3 Pipeline system ....................................................................................................
3.1.4 Power unit ...........................................................................................................
3.1.5 Reservoir .............................................................................................................
3.2 Design review objectives ........................................................................................
CHAPTER 4.0: METHODOLOGY
4.1 Observation of the existing water supply system .....................................................
4.2 Interview ................................................................................................................
4.3 Research .................................................................................................................
4.4 Reports from Pump manufacturers (Grundfos CAPS) .............................................
4.5 Physical data collection ..........................................................................................
CHAPTER 5.0: RESULTS
5.1 Discharge measured ................................................................................................
5.2 Calculation of the total head of the pipeline. ...........................................................
5.2.1 Head loss due to friction across pipeline (336 meter steel pipeline) ......................
CHAPTER 6.0: PROPOSED DESIGN FOR WATER SUPPLY SYSTEM
6.1 Description of the proposed design .........................................................................
6.2 Analysis of the Proposed Design.............................................................................
6.2.1Pipe (1) specifications: submersible pump to a reservoir .......................................
6.2.2Head loss Hf due to fluid friction in pipe ...............................................................
6.2.3Total head or dynamic head H across pipe ............................................................
6.2.4Pump (1) specifications ........................................................................................
6.2.5Pipe (2) specification: from booster pump to the main reservoir ............................
6.2.6 Head loss Hf due to fluid friction in pipeline ........................................................
6.2.7Total head or dynamic head H across the pipeline .................................................
6.2.8Pump (2) specifications ........................................................................................
6.2.9 Pipeline specifications for various discharges ......................................................
CHAPTER 7.0: DISCUSSION OF THE RESULTS .....................................................
CHAPTER 8: CONCLUSION AND RECOMMENDATIONS ....................................
8.1 Conclusion ............................................................................................................
8.2 Recommendations .................................................................................................
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8.2.1 Design for an underground reservoir ....................................................................
8.2.2 Design of a water recycling system ......................................................................
8.2.3 Design of a water management system.................................................................
8.2.4 Design of a rainwater harvesting system ..............................................................
BIBLIOGRAPHY ........................................................................................................
APPENDICES
Appendix 1: The Moody diagram ................................................................................
Appendix 2: Pump characteristic curve .........................................................................
Appendix 3: Pump characteristic curve ........................................................................
Appendix 4: Simplified Pump dimensions ....................................................................
Appendix 5: Pump and motor specifications .................................................................
Appendix 6 :Pump characteristic curve .........................................................................
Appendix 7: Power curve .............................................................................................
Appendix 8: Schematic representation of borehole and other specifications ..................
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CHAPTER I.0: INTRODUCTION
1.1 The history of The University of Nairobi
University of Nairobi started its inception in 1956 with the establishment of Royal Technical
College. Royal Technical College was then transformed into the second University College
of East Africa on 25thJune 1961 under the name Royal College on Nairobi and was admitted
into special relations with the University of London whereupon it immediately began
preparing students in the faculties of arts, science and engineering for award degrees of
University of London.
On 20th may 1964, Royal College Nairobi was renamed University College Nairobi as a
constituent college of inter-territorial, Federal University of East Africa with degrees
awarded being from Federal University of East Africa and not from the University of
London.
In 1970, the University College Nairobi transformed into the first national university in
Kenya and was renamed The University of Nairobi.(UON)
1.2 Water as a resource
Water is a resource that has been used since the existence of mankind. Water resources are
sources of water that are useful or have a potential use. Water is mainly used for agricultural,
industrial, household, recreational and environmental activities.
Most of the uses of water require fresh water but 97% of the earth’s water is salty. The
remaining 3% of fresh water is mainly found as groundwater, with only a small percentage
available above ground or in the air.
Water demand already exceeds supply in many parts of the world and as the world
population continues to grow so does the water demand. Expounding on the various uses of
water is:Agricultural: - 69% of worldwide water is used for irrigation.
Industrial:-22% of worldwide water is for industries. Major industrial uses are hydroelectric
dams, thermoelectric power plants which use water for cooling, ore and oil refineries, which
use water in chemical processes, and manufacturing plants, which use water as solvent.
Household:-water use for households includes drinking water, bathing, cooking, sanitation
and gardening which are estimated to be about 8% of the world’s use.
Recreation:-mostly the water is tied to reservoirs. Most of water for recreation includes
whitewater boating, anglers, water skiers, nature enthusiasts and swimmers.
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Environmental:-usually water used for this purpose is stored in impoundments and released
for environmental purposes, but more often is water retained in waterways through
regulatory limits of abstraction. Environmental water usage includes watering of natural or
artificial wetlands, artificial lakes intended to create wildlife habitat, fish ladder etc.
Due to the various uses of water in the daily lives of people and industries, water is becoming
a scarce resource and needs to be adequately managed in order to meet the daily demands.
Water stress has become a key issue in most parts of the world. Water stress is the situation
whereby there is not enough water for all the uses.
The most cause of water stress is population growth, expansion of business activity, rapid
urbanization, climate change, and depletion of aquifers.
1.3 Water supply in Kenya
Kenya like most parts of the world has failed to meet the demand of water with supply being
inadequately low. In the capital Nairobi, the supply is characterized by low levels of access
in particular the slums, poor service quality in the form of intermittent water supply. There is
also the occurrence of water pipes being stolen and sold to the scrap industry which affects
the supply massively.
Water in Nairobi was initially supplied by the Nairobi city council but the water section was
privatized and is now supplied by Nairobi city Water and Sewerage Company. Source of
water for Nairobi comes from Thika, sasumua and Ruiru dams and Kikuyu springs. The
estimated water demands for Nairobi as of 2010 was 650,000m3/day while the water supply
482,940 m3/day leaving a deficit of 167,000 m3/day. This deficit has led industries,
institutions and individuals to look for alternatives to this problem. Other problem facing
water supply in Nairobi is during the dry season when water levels in dams falls drastically,
this usually leads to water rationing which affects the whole population whether it’s for home
use or industrial.
The UN suggests that each person needs 20-50 litres of safe freshwater a day to ensure their
basic needs for drinking, cooking and cleaning. Source: World Water Assessment
Programme (WWAP). The average person in the developing world uses 10 litres of water
every day for their drinking, washing and cooking. (WSSCC)
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1.4 Water supply systems
A water supply system is created or expanded to supply a sufficient volume of water at
adequate pressure from the source to consumers for domestic, irrigation, industrial
firefighting and sanitary purposes. A primary concern for the engineer is estimation of the
quantity of water to be consumed by the community to help hi design adequately sized
components of the water supply system. Water supply systems consist of collection, storage,
transmission, pumping, distribution and treatment works.
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CHAPTER 2.0: LITERATURE REVIEW
2.1 Important definitions and terms
2.1.1 Pumps
A pump is a device used to move fluids, such as liquids, gases or slurries. A pump displaces
a volume by physical or mechanical action. Pumps fall into three major groups: direct lift,
displacement, and gravity pumps.(Fraenkel & FAO, 1986) Their names describe the method
for moving a fluid.
2.1.1.1 Well pumps
These are classified as centrifugal, propeller, jet, helical, rotary, reciprocating and air lift.
Centrifugal pumps are the most common for both shallow well and deep well velocity head
and pressure head.
2.1.1.2 Deep well pumps
These pumps have their impellers close enough to the water surface to eliminate cavitation.
The motor may be at ground level with a long shaft connecting it to the impellers or it may
be at the bottom of the well below and directly adjacent to the impellers. The former type is
called a deep well turbine pump and the latter a submersible pump. Submersible pumps can
be used in crooked wells while the turbine pumps can only be used in straight wells.
However the motors are difficult to reach for repair.
2.1.1.3 Centrifugal pumps
A centrifugal pump is a rotor dynamic pump that uses that uses a rotating impeller to create
flow by the addition of energy to a fluid.
Principle of operation
The process liquid like water enters the suction nozzle and then into the eye of the impeller.
When the impeller rotates it spins the liquid sitting in the cavities between the vanes
outwards and provides centrifugal acceleration. As the liquid lives the eye of the impeller a
low pressure area is created causing more liquid to flow towards the inlet. The impeller
blades are curved so as to push the liquid in a tangential and radial direction by the
centrifugal force. The kinetic energy of a liquid coming out of the impeller is harnessed by
creating a resistance to flow. The first resistance is created by the pump volute (casing) that
catches the liquid and slows it down. In the discharge nozzle, the liquid further decelerates
and it velocity is converted to pressure according to Bernoulli’s principle. (Grundfos)The
head (pressure in terms of height of liquid) developed is approximately equal to the velocity
energy at the periphery of the impeller expressed as;
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=
2
Where H = total head developed
=Velocity at periphery of impeller
g = acceleration due to gravity
Figure 2.1 Centrifugal pump
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Figure 2.2 Vertical centrifugal pumps
A= electric motor
B = drive coupling
C = lantern
D = radial bearing
E = outer column
F = shaft sleeve
G = ceramic bushing
H = impeller
I = delivery duct
L = intake duct
M = bushing
2.1.2 Total pressure head (H)
The total pressure head to be overcome by the pumping system. It is also referred to as
dynamic head because it incorporates the head loss due to friction in the pipeline which
arises only during the dynamic conditions of fluid flow. It is the sum of the static head and
the friction head.
The total pressure head is therefore given by the expression:
H = Hts + Hf
Where;
H = total or dynamic pressure head to be overcome by the pumping system;
Hs = total static head to be overcome;
Hf = pressure head loss due to fluid friction.
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2.1.2.1 Total static head (Hs)
The total static head (Hs) is the water level difference between the suction and delivery
reservoirs. This is shown in Figure 2. It depends on the site conditions between the two
reservoirs and the location of suction and discharge points on the reservoirs. It is determined
by a survey of site conditions.
2.1.2.2 The friction head (Hf)
The friction head is the total pressure head lost due to fluid friction which occurs as a fluid
flows in a pipeline. It includes the head loss due to pipe work and fittings starting from the
suction inlet fitting to the discharge pipe outlet. For a given discharge flow rate the friction
loss depend on the pipe material, size, length and the type and number of fitting and can be
compute once these specifications are determined.
There have been expressions developed for the velocity distribution and pressure losses
encountered during laminar flow which has Re < 2000 in closed circular pipes, this shows
that the flow is restricted to liquids that do not possess a high viscosity. Thus, in general,
turbulent flow conditions are more likely in most engineering situations even such as
pumping of water. Expressions will be developed for the losses incurred in turbulent flow in
both closed and open conduits. However, completely analytical solutions are not available
and that empirical relationships are needed in order to produce the necessary expressions.
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Figure 2.3 Flow through a conduit.
Considering a small element of fluid in a cross-section pipe as shown if Fig 2.1 above. The
flow is assumed to be uniform and steady so that the fluid acceleration in the flow direction
is zero. Applying the momentum equation to the fluid element in the flow direction yields
p1A- p2A - τolP + W sin θ = 0
Where P is the wetted perimeter of the element defined as part of the pipe’s circumference
which is in contact with the fluid, τo is the shear stress while LP is the area over which the
shear stress τo acts.
Now W= ρgAl and sin θ = −∆ ⁄
A (p1-p2) - τolP – ρgAΔz= 0
Where p1, p2 are the static pressures in the flow at sections 1 and 2. Hence
1
[( 1 − 2) −
]−
=0
Where the first term represents a drop in piezometric head along the pipe and the ratio A/P is
known as the hydraulic mean depth, normally denoted by m; thus,
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∗
τo=m
Where ∗⁄ is the rate of loss of piezometric head along the pipe and τo is the wall or
boundary shear stress.
Concept of friction factor f in introduced in the shear stress equation;
τo = f v2/2,
Where v is the mean flow velocity. Hence,
dp ∗
=
f v
2
If the frictional head loss down a length l of the conduit is denoted by hf, then the rate of loss
of piezometric pressure may be expressed as
dp ∗
=
f v
=
2m
ℎ
And
Hf= f
Now as
dp ∗
( +
=
),
Where z is the elevation of the pipe above some datum, then for open channels, as the static
pressure p may be assumed to be constant along the channel, it follows that
∗
=
=
θ
And since for uniform flow the hydraulic gradient hf/ is equal to the slope of the channel,
ℎ
=
Then it follows that;
f
=
So that
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v=
if
×√
=
is substituted, the expression known as the Chezy formula is obtained:
= ∁√
For pipes running full of fluid, the wetted perimeter becomes the internal circumference of
the pipeline; hence A/P=m=
/4 D = D/4, so the equation becomes for circular crosssections
ℎ =
4
2
This equation is known as the Darcy-Weisbach equation for head loss in circular
pipes.(Douglas)
If we say
=4 , ℎ
where λ is the friction factor read from the Moody diagram.
ℎ =
2
2.1.3 Suction design
There are two typical pumping system’s suction designs:
2.1.3.1 Positive static suction head arrangement (NPSH)
This is where the suction reservoir’s water level is above the pump center line. The positive
suction is shown as the positive head difference between the suction reservoir water level and
pump centre line.
2.1.3.2 Negative static suction head (NSSH)
This is where the suction reservoir water level is below the pump centre line. The negative
static suction, often referred to as the suction lift, is shown as the negative head difference
between the suction reservoir water level and pump centre line.
2.1.4 Pumping power
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2.1.4.1 Water Horsepower
Power required to pump water is determined by the flow rate and the total head generated as
shown below;
Water Horsepower
=
Where,
ρ= density of water in Kg/m3
g = gravity constant m/s2
Q = flow rate in m3/s;
H = total head in MoW
Once the design of the pumping system has been determined the water horse power that the
pump must inject into the water is fixed.
2.1.4.2 Pump shaft power
The power that must be injected into the pump shaft by the prime mover includes the water
horse power and other losses, namely;
1. Hydraulic losses in the pump.
2. Mechanical losses in the transmission shaft and the coupling between the pump
and prime mover.
The input power required at the pump shaft is given by;
=
∗
Where
ηp= overall pump efficiency
ηp = 0.55 for ratings of 5-10 Kw
ηp =0.65 for ratings of 10-20 Kw
ηp= 0.70 for ratings of 10-20 Kw
ηp= 0.75 for ratings of 20-30 Kw
ηp= 0.78 for ratings of 30-40 Kw
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ηp= 0.82 for ratings of above 40 Kw
ηc =efficiency of transmission coupling. This is 1 for direct coupling, 0.95 for V belt or gear
coupling and 0.8 for flat belt drive.
2.1.5 Electric motors
An electric motor is an electromechanical device that converts electrical energy into
mechanical energy. Most electric motors operate through the interaction of magnetic fields
and current-carrying conductors to generate force.
2.1.5.1 Electric motor power requirements
Electric motor speeds can be chosen to make direct coupling of the pump shaft appropriate.
The power input required by the electric driving motor can be determined as follows:
Pm =
∗
∗
Pm=power input required by motor
Ps= power input required by shaft
Af= altitude derating factor- 1% reduction for every 100 m above 1000 m.
Sf=safety factor. This is 1.5 for ratings up to 1.5 kW, 1.3 for 1.5-4 kW, 1.2 for 4-8 kW, 1.15
for 8-15 Kw, and 1.1 for above 15 Kw.
ηm= efficiency of motor
CHAPTER 3.0: OBJECTIVE STATEMENT
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3.1Existing University of Nairobi borehole water supply system
The University of Nairobi main campus borehole scheme comprises of the borehole, a pump,
the pipeline and the main reservoir.
3.1.1 Borehole
The borehole was drilled in 1993 with a depth of 250 metres and a capacity of16.1m3/h.
i.
ii.
iii.
iv.
v.
vi.
total depth =250m
static water level(SWL)=114m
Pumping water level(PWL)=195m
Casing Φ=152m
Test yield = 17.6m3/hr
Pump level below surface=226m
The water quality tested at the time was found to be with no sediment, odourless, tasteless
and clear. The temperature was found to be 30oc and it was within the specifications for
drinking and domestic applications as per the guidelines; (WHO, 2011)
3.1.2 Pump
The pump in use is a Grundfos sp 17-27 supplied by Davis & Shirtliff with a power rating of
15kWh. It is designed to work optimally at 16m3/hr with a total head of 225m.
Stainless steel corrosion resistance
Octagonal bearings with high velocity sand flush canals reduce abrasive wear
Replaceable wear rings long life of the impeller
Built in up thrust stop ring prevents damage during the critical start up
Inlet strainer limits passage of particles
Appendix 5: (Source from data manufacturer Grundfos (Davis and Shirtliff)
3.1.3 Pipeline system
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The pipeline system consists of;
3.1.3.1 Surface pipeline route
From physical examination of the route the following data was collected;
Distance to the reservoir from borehole surface is 132m. (This comprises of 22 pipes each of
length 6m.)
Elevation is 9m.
3.1.3.2 Pipe specifications
This includes the pipes used from the pump to the surface of the borehole and the
specifications are;
i) Rising mains from borehole surface to the pump location diameter is 63.5m
ii) Number of pipes = 32
iii) Length of each pipe = 6m
iv) Drop pipe length is = 6*32.5m=195m
v) Pipe material is galvanized iron.
vi) Total pipe length = 132+195+9=336m
vii) Static head Hs = 204 MoW
3.1.4 Power unit
This includes the type of power supply available which determines the kind of pump that can
be used. From physical examination of the site it was found that:
i.
ii.
iii.
iv.
Source; mains.
Three phase.
Distance from point to panel is 5m.
Distance from borehole to panel is 10m.
3.1.5 Reservoir
The main reservoir is at the top floor of Hyslop building University of Nairobi main campus.
It receives water directly from the borehole and redistributes it to other reservoirs. It has a
storage capacity of 16m3. It is made of steel. (Source; physical examination)
Other reservoirs details include:
i.
Jomo Kenyatta Memorial library 3 wings 3 tanks in each wing of capacity
4.6m3 = 41.4m3.
ii.
British wing (mechanical building) 2 wings 4 tanks @ 4.6m3=36.8m3
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iii.
iv.
v.
vi.
vii.
viii.
ix.
x.
xi.
American wing 2 tanks each of capacity 4.6m3=9.2m3
Civil block I tank = 16m3.
Education building 1 tank of 16m3.
Central administrations block 2 tanks @ 10m3.
Gandhi wing 1-finance tank of 16m3.
Post graduate 2 tanks @ 18m3.
Estates department 1 tank @ 4.6m3.
Nuclear science building 2 tanks @ 4m3=8m3.
Workshop 2 tanks @ 4.6m3=9.2m3.
Total storage capacity available= 229.2m3.
3.2 Design review objectives
The objective of the project was to review the design of University of Nairobi main campus
borehole water supply system.
The aim was to find out if the current design meets the current water demand with the
increased population.
The design was done to meet the estimated demand at the time of 2500 people with a 10
hours peak demand of 125m3/day.
A review is necessitated by the increase in population from 2500 people to approximately
4500 people.
CHAPTER 4.0: METHODOLOGY
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4.1 Observation of the existing water supply system
From the observation of the water supply system, it was observed that it had four major
components: the borehole, submersible pump, pipeline system and the main reservoir tank.
The submersible pump has been lowered into the borehole and it is also attached to power
supply system. The pump delivers water through the pipeline system which is of the required
diameter to deliver the required discharge and total head to the main reservoir.
A meter has been placed at the top of the borehole to record the discharge from the pump
during its working.
4.2 Interview
Some pump workings and data were provided by the maintenance personnel who also
provided information on the pumping hours. They also provided information on how
maintenance is done and any challenges they face anytime a break down occurs during the
year.
4.3 Research
Research was done from the internet, books on engineering design and fluid mechanics. This
was used to find ways of calculating the water demand, head loss due to pipe friction, pump
and pipeline specifications. Research was also done on ways to improve the water supply
system in order to ensure the proper usage of water because a lot of wastage goes on
especially during cleaning and irrigation of plants.
4.4 Reports from Pump manufacturers (Grundfos CAPS)
We managed to get the pump characteristic curves, pump data, motor data and drawings.
These were used in to analyse the results obtained.
4.5 Physical data collection
We managed to collect meter readings of the pump to get the flow rate per hour. This
information was of use in the analysis of the system.
CHAPTER 5.0: RESULTS
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5.1 Discharge measured
The data collected was initially done at ten minute intervals, followed by fifteen minute
intervals and a half hour interval. The data collected was done around midday. The values
were read from the meter at the borehole surface.
Table 5.1 Discharge data per 10 minute interval
DISCHARGE, Q (M3)
96560
96561
96563
96565
96566
96568
96569
96571
96572
96574
TIME hrs. (10 minutes
interval)
1028
1038
1048
1058
1108
1118
1128
1138
1148
1158
Discharge = 9 m3/hr.
Table 5.2 Discharge data per 15 minute interval
DISCHARGE, Q (M3)
96773
96777
96780
96782
96784
96787
TIME hrs. (15 minutes
interval)
1127
1142
1157
1212
1227
1242
Discharge = 11 m3/hr.
Table 5.3 Discharge data per ½ hour interval
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DISCHARGE, Q (M3 )
97771
97775
97780
97784
97789
97794
Average Discharge =
TIME hrs. (½ hour interval)
1100
1130
1200
1230
1300
1330
10 m3/hr.
=
The total average discharge Q =
m3/hr.
5.2 Calculation of the total head of the pipeline.
5.2.1 Head loss due to friction across pipeline (336 meter steel pipeline)
The pipeline specification from the pump to the main reservoir is as follows;
1.
2.
3.
4.
Pipeline material is steel.
Pipeline length = 336 metres
Static head across pipeline = 195 + 9 = 204 m
Discharge through the pipeline =10 m3/hr
Assuming a surface roughness of 1mm for the 63.5mm diameter * 336 metre of steel pipe
material.
Relative roughness of selected pipe ( ⁄ )
K = 0.1 mm,
d = 63.5 mm
⁄ = 0.1/63.5= 0.0157
Reynolds number of flow in pipe of diameter d=63.5 mm
Discharge through the pipe Q= 10 m3/hr
Flow velocity U=
=
∗
∗ ∗ .
= 0.88 m/s
Reynolds number for flow is given by
Re=
=
.
∗ .
∗
= 55880
Using moody diagram for re= 55880 and k/d = 0.0157 the coefficient of fluid friction =
0.0375
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Head loss due to fluid friction in pipeline
From Darcy equation
Hf=
=
.
∗
∗ .
∗ .
∗ .
= 7.83
Hf = 7.83 metres of water (MoW)
Total head to be overcome across the steel pipeline
Htotal= Hs + Hf = 204 + 7.83 = 211.83 MoW
Table 6.1 Characteristic data for the existing system
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Internal
diameter
(mm)
63.5
discharge
(m3/hr)
0
10
11
12
13
14
15
16
17
CHARACTERISTIC DATA FOR THE EXISTING PIPELINE SYSTEM
Internal
Relative
Kinemati Pipeline
roughnes roughness
c
length
sk
k/d
viscosity (m)
(m2/s)
0.1
0.00157480 0.000001 336
3
diameter, velocity
Reynolds λ(from
head
head Hf static
d (m)
(m/s)
’s no.
Moody
Hf
(MoW/
head
(Re)
diagram (MoW m)
(MoW)
)
)
0.0635
0
0
0
0
0
204
0.0635
0.88
55880
0.0375
7.83
0.02330 204
0.0635
0.96
60960
0.0370
9.19
0.02735 204
0.0635
1.05
66675
0.0365
10.85
0.03229 204
0.0635
1.14
72390
0.0360
12.44
0.03702 204
0.0635
1.23
78105
0.0350
14.28
0.04250 204
0.0635
1.32
83820
0.0340
15.98
0.04756 204
0.0635
1.40
88900
0.0335
17.71
0.05271 204
0.0635
1.49
94615
0.0330
19.76
0.05881 204
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total head
(MoW)
204
211.83
213.19
214.85
216.44
218.28
219.98
221.71
223.76
Graph 5.1 Superimposed graph for the pump and pipeline
Total head (moW) vs Discharge (m3/hr)
350
300
250
200
150
100
50
0
0
2
4
6
8
10
12
14
16
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18
Table 5.4 Summary of results
Summary of results
Pump design
parameters
Discharge in m3/hr.
Total head
Pipeline size( in)
Pipeline length (m)
Pump power-p2 (kW)
Motor power-p1 (kW)
Pump efficiency (%)
Motor efficiency (%)
Overall efficiency (%)
Current (A)
Rotation speed (rpm)
Operating hours
Reservoir capacity (m3)
16
225
2.5
336
13.5
16.2
73.2
82.9
60.7
29.4
2878
14
16
Pump
performance at
actual discharge
10
280
2.5
336
11.5
13.8
82
24
2900
18
16
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CHAPTER 6: PROPOSED DESIGN FOR WATER SUPPLY SYSTEM
The existing water supply system has a discharge of 10 m3/hr which translates to 180 m3/day
which falls below the expected value of 225m3/day. This deficit has led to a proposal of the
review of this design by using a submersible pump with a booster pump to increase the
discharge to the main reservoir.
6.1 Description of the proposed design
The proposed design is composed of the following components;
i.
ii.
iii.
iv.
A submersible pump (the current pump will be used).
A booster pump
A 200m3 reservoir on the ground.
The pipeline ~ 336 m length.
The proposed design is meant to ensure the water demand in University of Nairobi is met
while also taking care of the pump by reducing the number of working hours. Since the main
reservoir is supposed to store water from the borehole and then distribute it to the rest of the
reservoirs in the main campus of University of Nairobi there is a need for its capacity to be
increased so that it can store a larger amount of water so that the pumping hours can be
reduced.
The pump would be running for 14 hours a day which means a discharge of 224m3/day.
From the borehole the submersible pump pumps water to a surface reservoir which is then
connected to a booster pump which pumps water from the first reservoir to the second
reservoir located on top of Hyslop building. From the reservoir at Hyslop building water is
distributed to other buildings in University of Nairobi main campus by gravity where then
water is pumped on top of buildings by using booster pumps.
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200,000 litres reservoir
Submersible pump
Figure 6.1 Diagrammatic representation of the proposed system
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6.2 ANALYSIS OF THE PROPOSED DESIGN
6.2.1Pipe (1) specifications: submersible pump to a reservoir
Pipeline material – steel
Pipeline length – 195 m
Static head across pipeline – 195 m
Discharge through the pipeline – 16m3/hr
Surface roughness k is 0.1 mm for a pipe diameter of 63.5 mm
Relative roughness of pipe k/d
k/d=
.
.
= 0.001574803
Velocity through pipeline v
v=Q/A=
/
=
∗
= 1.4 m/s
∗
Reynolds’s number for the pipe
Re =
∗
=
. ∗ .
= 88900
∗
Coefficient of fluid friction
The value of
for the pipe
is got from the Moody diagram using Re and k/d
Re=88900, k/d=0.001574803, =0.033
6.2.2Head loss Hf due to fluid friction in pipe
From the Darcy equation
Hf=
= 0.033
.
.
∗ .
= 10.12 MoW
6.2.3Total head or dynamic head H across pipe
H=Hs+Hf
H=195+10.12
H= 205.12 MoW
6.2.4Pump (1) specifications
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The submersible pump requirements are a discharge Q of 16m3/hr and to overcome a total
head H of 205.12 MoW. The pump specifications will be found from the manufacturer and to
check which pump will at the very least come close to these requirements.
6.2.5Pipe (2) specification: from booster pump to the main reservoir
Pipeline material-steel
Pipeline length 141 m
Static head 141 m
Discharge through pipeline 16 m3/hr
Relative roughness of pipe k/d
K/d= 0.1/63.5= 0.001574803
Velocity flow through pipe
Velocity v= 1.4 m/s (same as previous pipeline)
Coefficient of fluid friction
in pipe
From the moody diagram using Re and k/d
=0.033
6.2.6 Head loss Hf due to fluid friction in pipeline
Hf=
= 0.033
.
.
∗ .
= 7.32 MoW
6.2.7Total head or dynamic head H across the pipeline
H= Hs+Hf
H=141+7.32
H=148.32 MoW
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6.2.8Pump (2) specifications
The pump needed needs to meet the required discharge Q of 16 m3/ hour and to overcome a
total head of 148.32 MoW. The kind of pump required will be checked from the
manufacturer’s pump characteristic curves that would be able to provide that kind of pump
6.2.9 Pipeline specifications for various discharges
Since head in terms of meters of water is going to be checked for various discharges (m3/hr)
of: 10, 11, 12, 13, 14, 15, 16 & 17 only one sample calculation will be done.
For a discharge of 1 m3/hr the various calculations will be;
d=63.5 mm, v=1*10-6 m2/s, g=9.81m2/s, k=0.1mm
Velocity, V =
,
Surface roughness =
≈ 0.09 m/s
=
,
∗ .
.
.
= 0.001574803
Reynolds’s number, Re=
=
.
∗ .
= 5715
∗
From the moody diagram, checking for the value of lambda λ, using the Reynolds’s number
and surface roughness we get;
λ= 0.0375
Frictional head Hf=
∗ ∗
=
.
∗
∗ .
∗ .
∗ .
= 7.8318MoW
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CHAPTER 7.0: DISCUSSION OF THE RESULTS
The objective of the experiment was to review the University of Nairobi borehole water
supply system to check whether it meets the required water demand for the population of the
institution.
The design of the system was supposed to deliver a discharge of 16 m3/ hour while the pump
ran for 10 hours a day; this would result to a discharge of 160 m3 which would have met the
required water demand at the time of the design which was at 125 m3/day. This was meant to
serve a population of 2 500 people in 1993.
The actual discharge of the pump was found to be 10 m3/hour.The data was collected from
the meter readingson the borehole surface. This was done during the day when the pump
would probably be at its peak. The pump runs for approximately 22 hours a day.
The friction head in the pipeline (Hf) was found to be 7.83 MoW while the static head (Hs)
was found to be 204 MoW. Therefore the total head or dynamic head (H) is 211.83 MoW.
From the pump characteristic curve provided by the manufacturer (appendix) it was found
that for a discharge of 10 m3/ hour, the total head to be overcome by the pump is 280 MoW.
The pump and pipeline characteristic curves were superimposed as shown in graph 5.1. It
was observed that the actual discharge is supposed to be 16m3/ hour with a total head of 225
MoW. This is according to the manufacturers design. Ideally, the pump characteristic curve
and the pipeline characteristic curve should have intersected at the actual discharge. This was
not the case. This could be due to the following reasons:
1. The manufacturer’s pump characteristic curve may not be correct. This can be
verified by carrying out a pump test.
2. The assumptions made while calculating the total head in the pipeline. The effect of
fittings, pipe bends and valves was not considered. Also the surface roughness of 0.1
mm was an estimate.
3. The residue head was not taken into account.
The main reservoir tank was found to have a capacity of 16 m3 which considering the water
demand required is very small. The reservoir needs to be large enough so that it can hold
more water for the pump to run for short hours while providing water for emergencies such
as pump maintenance and repair. Although the main reservoir distributes to other reservoirs
in the main campus when the water demand is at peak the reservoir holds water for a few
hours only thus this ensures the pump will run for longer hours.
The current water demand for the main campus stands at 225 m3/day for an estimated
population of 4500 people. The pump runs for approximately 22 hours which translates to
220 m3/day thus that translates to a deficit of 5m3/day.
From the data collected and comparing to the water demand required per day it has been
noted that the system is failing to meet the required water demand considering that the
institution uses water for other purposes such as cleaning, irrigation and laboratory work.
Also the running of the pump at close to 24 hours a day can lead to the pump losing its
efficiency and being worn out quickly.
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The proposed design for the water borehole is meant to alleviate the total head the
submersible pump is supposed to overcome while providing the required water demand. The
proposed design also addresses the issue of reservoir capacity by increasing the capacity of
the reservoir to 200 m3 from the submersible pump to the first reservoir and also increasing
the second reservoir capacity 54m3, this is to ensure the pump runs for fewer hours by having
a larger capacity.
The challenges facing this borehole water supply system is getting the required pump to meet
the water discharge required and to overcome the total head required. This can be observed
from the existing borehole water supply system which was designed for a water discharge of
16 m3 but with the actual discharge reducing to 10 m3. From the driller’s report it the total
discharge to be pumped from the borehole was 17.3 m3/hour it was observed during
weekends that water availability in the main campus was drastically reduced because the
pump was running the full hours required to meet water demand but this is due to reduced
water demand during weekends but this has led to a situation whereby the loos are being left
without water in various buildings and this leads to a very foul smell from the toilets. It was
also observed that a lot of water is used for cleaning of buildings which also comes from
borehole water supply system and also for irrigation of trees, grass and flowers.
CHAPTER 8: CONCLUSION AND RECOMMENDATIONS
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8.1 CONCLUSION
The objective of this project was reviewing the design of the University of Nairobi main
campus borehole water supply system to check if the water demand for the main campus was
being met.
From the results gathered it was observed that the discharge from the submersible pump was
10 m3 /hr which was running for approximately 22 hours a day during weekdays which
translates to 220 m3/day against a required water demand of 225 m3.The initial design was
for 125 m3/day for a population of 2500 people which was being met initially but with time
the population has doubled which has rendered the existing water supply system to be
redesigned or a new design to be made to meet the current water demand of 225 m3.
The proposed design was made with consideration to the existing system such that there
would not be much inconvenience in installing it with only the addition a booster pump and
two larger capacities of reservoirs being required. This proposed design is meant to provide
the required water demand with the pump discharging at 16 m3/ hour for 15 hours a
daywhich would translate to 240m3/day which surpasses the current required demand of
225m3/day. The excess could cater for future increase in water demand.
8.2 RECOMMENDATIONS
From the results and data collected, there needs to be some few adjustments to the system for
it to meet the required water demand.
8.2.1Design for an underground reservoir
The main reservoir has a capacity of 16 m3 which considering the water demand is too low to
hold water to meet that demand. The reservoir needs to hold a large capacity of water such
that it can still provide water in case of emergencies such as breakdown of pump and routine
maintenance of pump.
8.2.2 Design of a water recycling system
From what has been observed from the main campus usage of water, a lot of water goes to
cleaning of offices, lecture halls and corridors which goes up to early morning. Sewage
water, water from laboratories and water for cleaning clothes and utensils can be recycled
and reused for irrigation and as cleaning water for offices, lecture halls and corridors.
8.2.3 Design of a water management system
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Water management system is allocating water resource in a sustainable and efficient manner.
This involves planning, developing, distributing and managing optimum use of water
resources. This is supposed to meet all the required water demand by equitable basis.
8.2.4 Design of a rainwater harvesting system
During the rainy season water is not required for irrigation because there is water available
from the atmosphere, but during the dry season, the same water that is being used to meet the
water demand for the population is also being used for irrigation thus there is a need to
harvest the water and use it during the dry season
BIBLIOGRAPHY
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1. Douglas, J. G. Fluid Mechanics. Third Edition.
2. Fraenkel, P. L., & FAO, D. (1986). Retrieved 2012 2012, from Wikipedia.:
http://en.wikipedia.org/wiki/Pump
3. Grundfos, R. The Centrifugal Pump. Grundfos.
4. UON. (n.d.). www.uonbi.ac.ke.
5. WHO. (2011). Guidelines for drinking water quality 4th edition. WHO.
6. Previous year report GON 01/2011
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Appendix 1: The Moody diagram
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Appendix 2: Pump characteristic curve
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Appendix 3: Pump characteristic curve
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Appendix 4: Simplified Pump dimensions
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Appendix 5 Pump and motor specifications
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Appendix 6 Pump characteristic curve
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Appendix 7 Power curve
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Appendix 8 Schematic representation of borehole and other specifications
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