Download - Groundwater & pumps
Energy & Environment
Distribution of the World’s WaterHow much of the World’s water is fresh & available?
Our main source of water is groundwater
Hydro Cycle Revision
Lakes and Streams
Rain
Groundwater
Water in the world is reused
As well as being the largest % of fresh water, what else is good about groundwater
Revision of Permeability
SandClay
Clay isImpermeable
Sand is Permeable
Permeability of Rock
Rock
Cracks in rock
Water travels through cracks in rocks
If no cracks then water cannot move
Advantages of ground water
Water is filtered through sand and gravel
Sand is Permeable
Reduced risk of contamination Stays at a stable temperature
More chance of water availability in summer
Ground Water Storage: Aquifers
Storage of groundwater
Movement of water through the ground /rocks
Saturated Zone
Unconfined Aquifer
Non permeable rock/clayNo cracks for water to move
Unconfined Aquifer
A pump is required to overcome this head
Water Table
This difference in height is called the head required.
Confined / Artesian Aquifer
Non permeable rock/clayNo cracks for water to move
Water in aquifer is trapped so pressure builds up
Artesian/Confined Aquifer
No pump required if head required < pressure in aquifer
If head required> pressure in aquifer then pump is required
HeadWhere you want to collect water from
A pump is required to overcome this head
Where water is (water table)
This difference in height is called the head required.
Where would you build your well?
B
D
Non permeable rock/clay
A
C
Shortest well, so smallest head required & also close to house
Where would you build your well?
AC
B
What are the issues with your choice?
Wastage of water?Storage Needed?
Effect of well on Water tableWhat do you think will happen when we build a well?
Original Water Table
Effect on other wells
Original Water TableDrawdown
Summary DrawingExplain this drawing
What type of Well?
Hand dug-normally quite shallowOpen to pollutionEven the bucket and rope can contaminate the water supply
Bored or Drilled WellDeep narrow wellProtected from pollutantsCan safely abstract water
Digging WellsHand drilledCant get that deepLimited amount of waterUse an auger
Jetting wellsUse of water to loosen soil and carry it to surface Sand/gravel/clay –not rock
Machine drilled boreholesDrilling rig & crewTime and moneyPercussion drillingRotary drilling
Not advised to drill into hard rock-not easy to
find connecting cracks
After drilling, borehole will need casing or well
will need bricks to support it
Machine Drilled Boreholes: Cable Percussion Drilling
Tripod
Falls by gravity
Drilling shallow boreholes Low cost & minimum disruption
Not good for rock
Exerts downward pressure and drills rotationally all the way down
Sharp, rotational drill bit rotates round
Machine Drilled Boreholes: Rotary Drilling
Well YieldImportant to know the yield of the well so we know what pump to use
Prevent drawing down the well too much or effecting other wells
A pumping test is done to estimate the yield of the borewell
The Yield of an aquifer depends on the 1. Amount of water available2. Rate at which it can be extracted
Depends on soil type or amount of cracks in the rock
Pumping Test Pump well for 8 to 48 hours.
Normally carried out by specialist contractors
Tests the balance between the max volume of water pumped out and recharge
Recharge
Recharge
Rate of water pumped=volume/time
Drawdown
Distance to new water level/time
Balance achieved when water level stops dropping. This is the yield
Calculating Head Required: If Pump Below WaterTotal head to overcome=Static + Friction-Suction head
Bend in pipes etc
Height difference between two water bodies
Head needed to get to pump
Calculating Head Required: If Water Below PumpTotal head to overcome=Static + Friction + Suction head
Bend in pipes etc
Height difference between two water bodies
Head needed to get to pump
Types of Pump: Positive Displacement
Due to pressure change, water is sucked up
Liquid is physically displaced
Liquid is physically displaced
Fixed volume of liquid pumped up each time
e.g. Handpump
Hand Pump
Depth= 50m or less
Rising Main carries the water to the outlet
Heavy pump handle to balance with the inside of the pump to make it easy for user.
Pump cylinder pushes water to rising main
Rod connects handle to piston
Valve
Valve
ScreenPrevents stones and gravel but allows water through
Foundation prevent contaminating supply
Hand Pump
Suction pulls water up
Foot valve open from suction
Check valve closed
Suction pulls water up
Piston moves through water and
displaces water
Foot valve open from suction
Check valve closed
Check valve open from gravity
Foot valve closed from weight of water
Hand Pump
Foot valve closed from weight of water
Check valve open from gravity
Piston moves through water and
displaces water
Check valve open from gravity
Foot valve closed from weight of water
Piston reaches bottom of cylinder.
Foot valve closed from weight of water
Check valve closed
Piston gets pulled up and displaces the water on top of piston. Also sucks up
more water from borehole
Make your own Displacement Pump
Make your own Displacement Pump
Types of Pump: RotodynamicMachine which moves quickly and passes this kinetic energy onto a liquid.
If speed of pump increases=discharge & pumping head increases
e.g. centrifugal pump
Water(little speed)
Water(lots of speed)
Centrifugal Pumps
Water(little speed)
Wat
er(l
ots o
f spe
ed)
Impeller gives water energy
Casing forces water through
small space
Shaft turned by electric/diesel
motor
Fast
wat
er
push
ed
thro
ugh
smal
l are
a
Centrifugal Pumps
Impeller spins the water round accelerating it.
Casing forces speed of water to decrease as less area, this increases the pressure. Water gets lifted due to this pressure
Pressure = ForceArea
Force=mass x acceleration
Operation of a Surface Mounted Centrifugal PumpNever run pump dry
If the pump is above the waterbodythen it cannot pump only air. It needs primed
Better to start the pump against a closed valve-this reduces the power needed for start
Priming means the pump casing has to be filled with water before starting the pump.
Multistage Pump
Series of centrifugal pumps
If the required head cannot be met by one centrifugal pump then a multistage pump is used
Pressure of liquid is increased in stages
Used for boosting water pressure and in submersible borehole pumps
Can block easily and become damaged –so only good for very clean water
Submersible Centrifugal PumpsWaterproof pump
Ensure pipe does not dry out
Water enters here
Push fluid to the surface
Typically multistage centrifugal pumps operating in vertical position
Power supply
Series of impellers
Make your own Rotodynamic Pump
Make your own Rotodynamic Pump
Make your own Rotodynamic Pump
Simple Jet Pump
Underwater part of a deep well jet pump
Pressure pipeHalf of water sent back through
Cone shaped nozzel
Suction Pipe
Venturi throatReduce area so increase Pressure
Venturi
Speeds up the water causing a pressure drop. This sucks in more water .
High pressure
High velocity
Low presureQ=velocity x area
Change in pressure is related to change in velocity
Simple Jet PumpJet pumps are designed to pump large volumes of water
What pump to use?Pump Type Lifting from
wells or boreholes
Abstract from rivers & lakes
Distributethrough pipeline
Surface mounted centrifugal
Electric submersible multi-stage centrifugal
Hand pump
Selecting the correct pumpBased on head to overcome and flow need to pump
Pump Curves from suppliers
Head(m)
m3/s
Vigyan Ashram Pump ExerciseCarry out a tour of Vigyan Ashram’s pumps
Complete the below table with all the information you can find out
Location Type of pump
Head Power Rating
How could this pump/well be improved?
Vigyan Ashram Pump Exercise
How could you improve these pumps? This should be your next environment project!
To select the correct centrifugal pump1. Calculate the flow rate. This will depend on the water use.
2. Calculate the static head.
3. Calculate the friction headThis will include the friction over the length of pipe and the friction from local bends etc
4. Calculate the total head (static + friction)
5. Use Pump curves from suppliers to find the correct pump
Pump Head Example
10m
8m
5m
Calculate the head a submersible pump down this borehole would require
You need to fill a 900 liter tank
Due to cost of running a pumpand unreliability of electricity,you aim to fill this tank in 30mins.
So Flow required= 900 liters = 30 liters = 0.5 liters
30 mins 1 min second
Assume you are using a 15mm internal diameter PE pipe
1.What is the flow needed from the pump?
Pump Head Example
10m
8m
5m
8m
5m
2.What is the static head?
Hstatic=8 +5= 13m
Pump Head Example
10m
8m
5m
A. Losses due to the length of the pipe (affected by the type of material)B. Local losses due to bends in the pipe and entry and exit
3.What are the friction head losses? Remember these are due to:
Pump Head Example
10m
8m
5m
Hf = 10.9L x Q 1.85
C 1.85 x D 4.87
Use the Hazen Williams formula to calculate the friction losses due to length of pipe
3.What are the friction head losses? First lets look at losses due to the length of the pipe.
Pump Head Example: Hazen Williams Formula
Hf = 10.9L x Q 1.85
C 1.85 x D 4.87
Frictional head loss (m)
Length of pipe (m)
Flow (m3/s)
Coefficient
Internal diameter of pipe
Pump Head ExampleL= 8m + 10m +5m=23m of pipeHf = 10.9L x Q 1.85
C 1.85 x D 4.87Q= 0.5l/s =0.0005m3/s
C= 150 for PE & PVC Pipe
D= 15mm= 0.015m
Hf = 10.9 x 23 x 0.0005 1.85
150 1.85 x 0.015 4.87
Hf=15m
Friction losses from the length of the pipe is Hf=15m
10m
8m
5m
Pump Head Example
10m
8m
5m
You can also use tables from suppliers to calculate the head loss due to length of pipe
Hf = 23m x 0.9=20.7m
3.What are the friction head losses? First lets look at losses due to the length of the pipe.
Pump Head Example
10m
8m
5m
hL= (3 x kL 90°bends + kL entrance + kL exit) x v2
2g
kL values90°bends =1Plain suction entrance=0.9Sharp exit=1Entry Loss
Exit Loss
hL= kL v2
2g
Coefficient of bend/entry/exit
gravity
Velocity
hL= (3 x 1+ 0.9+ 1) x v2
2g
3.Now lets look at local losses due to bends in the pipe and entry and exit
Need to find the velocity of the water. V=Q/A
Pump Head Example
Q= 0.5l/s =0.0005m3/s
Cross sectional area of pipeA=Πxd2
4A=3.14 x 0.0152
4A=0.000177
0.015m
V= Q = 0.0005 =2.83m/sA 0.000177
hL= (3 x 1+ 0.9+ 1) x v2
2ghL= (3 x 1+ 0.9+ 1) x 2.832
2 x 9.81=2m
So local friction losses account for 2m of head
Pump Head Example
10m
8m
5m
hL= 2m
hk= 15mA. Losses due to the length of the pipeB. Local losses due to bends in the pipe and entry and exit
3. S0 the friction losses are:
Pump Head Example
10m
8m
5m
Calculate the total head required
hL= 2m(due to local losses)
Hk )= 15m(due to length of
pipe)
+hstatic= 23m +Total head = = = 40m
Can you think of any ways to reduce this head?
The more head we have to overcome the more energy we need to use.
Reduce number of bendsChose a bigger diameter pipeChose a smoother materialHave bell shaped entry
Pump Head Example
Head(m)
m3/s
40m
0.0005m3/s
So to find a suitable pump. You need to look at pump curves.
Suitable pump