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