BASIC MECHANICAL ENGINEERING

UNIT-3

1)Hydraulic Pumps And Turbines

2)Refrigeration And Air Conditioning Systems

HYDRAULIC MACHINERY

HYDRAULICS

Hydraulics deals with the mechanical properties of liquids.

Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties.

Hydraulics is used for the generation, control, and transmission of power by the use of pressurized liquids.

Pipe flow, dam design, fluidics and fluid control circuitry, pumps, turbines, hydropower, computational fluid dynamics, flow measurement, river channel behavior and erosion.

TOPICS 1. Hydraulic pumps

a. Reciprocating pump

b. Centrifugal pump

2. Hydraulic power plant layout

3. Hydraulic Turbines

a. Impulse

b. Reaction

HYDRAULIC PUMP

Mechanical device which converts the mechanical energy into hydraulic energy.

Increase the pressure energy subsequently converted into potential energy.

A pump is a device which lifts water from a lower level to a higher level at the expense of mechanical energy.

Pump is a Power absorbing device.

RECIPROCATING PUMP

As the crank moves outwards, the piston moves out creating

suction in the cylinder.

Due to the suction water/fluid is drawn into the cylinder through

the inlet valve.

The delivery valve will be closed during this outward stroke.

During the return stroke as the fluid is incompressible, pressure

will developed immediately which opens the delivery valve and

closes the inlet valve.

During the return stroke fluid will be pushed out of the cylinder

against the delivery side pressure.

CENTRIFUGAL PUMP

Energy is imparted to the fluid by centrifugal action of moving blades from the inner radius to the outer radius.

The main components of centrifugal pumps are (1)the impeller, (2)the casing (3)the drive shaft

The impeller consists of a disc (impeller) with blades mounted

perpendicularly on its surface.

The casing is air tight and water tight and its cross sectional

area gradually increases towards the outlet

The upper end of the suction pipe is connected to the eye of the

impeller and other end to foot valve

The delivery pipe is connected to the outlet of the pump to

deliver liquid to the required height with the help of delivery

valve

WORKING

The fluid enters through the suction nozzle of the pump to

the eye of the impeller.

The fluid is trapped between the blades of the impeller.

The impeller is spinning at the velocity of the driver.

As the fluid passes from the eye, through the blades toward

the outside diameter of the impeller, the fluid undergoes a

rapid and explosive increase in velocity

As velocity goes up, the pressure goes down, and indeed

there is a low-pressure zone in the eye of the impeller

The liquid that leaves the outer diameter of the impeller

immediately slams into the internal casing wall of the

volute where it comes to an abrupt halt

As velocity goes down, the pressure increases

The velocity is now converted into head or pressure

available at the discharge nozzle.

PRIMING To start delivery of the fluid the suction pipe, casing, impeller

and the delivery pipe up to delivery valve should be filled with

the fluid without any air pockets. This is called priming.

In presence of air, negligible pressure is generated because of

low density of air and hence no water will be lifted

Delivery valve is kept closed even after the casing is filled with

water.

Then delivery valve is opened gradually to allow high velocity

and high pressure water to push through the delivery pipe.

CENTRIFUGAL PUMP RECIPROCATING PUMP

Large discharge and small heads

Small discharge and higher heads

Lifting of high viscous fluids like oils, paper pulp, chemicals

Can handle only pure water and less viscous fluids

Uniform and continuous flow

Flow is fluctuating and pulsating

Higher speed and hence coupled with motor

Runs at low speed hence gear driven

Needs priming Priming not required

Quiet in operation Noisy in operation

Maintenance is cheap costly

Less wear and tear More wear and tear

Occupies less space 4 to 6 times larger area

Efficiency is less Efficiency is more

HYDRAULIC TURBINE

Hydraulic turbines are machines which convert hydraulic energy (energy of water ) into mechanical energy.

Thus in turbines fluid does work on the machine and machine produces power.

The mechanical energy developed by the electric generator which is directly coupled to the shaft of the turbine.

The electric power developed by the electric generator is known as hydro electric power. So the generation of hydro electric power is cheaper than the other sources like coal, oil, etc.

HYDRO POWER PLANT LAYOUT

SHAFT CONNECTING TURBINE & GENERATOR

TUNGABHADRA

6 X 9 MW KAPLAN,

2 X 9 MW FRANCIS

SRISAILAM

6 X 165 MW Kaplan

6 X 110 MW Francis

NAGARJUNA SAGAR

1 X 110, 7 X 100,8.

5 X 30 Francis

HYDRAULIC TURBINES

Machines which convert hydraulic energy in to

mechanical energy.

Fluid does work on the machines, produces power

Power developed is called hydro electric power

Principal component of turbine is rotor

CLASSIFICATION 1.Action of waterImpulse : There is no pressure drop on the runner/rotor. K.E of water coming

from the jet is used to run the runner/rotor. Ex: Pelton wheel turbine.

Reaction: There is a loss of K.E as well as pressure energy on the runners of the blade.

Ex: Francis turbine

2. Direction of flow of waterTangential: In this flow the water strikes the runner tangential to the path of

rotation. Ex: Pelton wheel turbine.

Radial: In this flow the water enters the runners radially and comes out axially. Ex: Francis turbine

Axial: In this flow the water flows parallel to the axis of the turbine. Ex: Kaplan turbine

CLASSIFICATION3. Available head

High head: The turbine capable of working under high potential head of water above 250m

Ex: Pelton wheel turbine.

Medium head: The turbine is capable of working under medium range of potential head about 60m to 250m

Ex: Francis turbine.

Low head: The turbine is capable of working under low range of potential head greater than 60m

4. Specific speed:

Low speed: Turbine works in the range of 10-50. (Ex: Pelton wheel turbine)

Medium speed: Turbine works in the range of 50-350. (Ex: Francis turbine)

High speed: Turbine works in the range of 10-50. (Ex: kaplan turbine)

IMPULSE TURBINE The available energy of water is converted into kinetic

energy by passing it through a nozzle at the end of the penstock

Water coming out of nozzle forms into free jet which impinges on a series of buckets of the runner, causing it to revolve

Water is in contact only with a part of the runner at a time A casing is provided on the runner to prevent splashing

and to guide the water discharged from the buckets to the tailrace

REACTION TURBINE At the entrance to the runner only a part of the available

energy of water is converted into kinetic energy and a suitable part remains in the form of pressure energy

As the water flows through the runner the change from pressure to kinetic energy takes place gradually

For this gradual change in pressure to be possible the runner must be enclosed in a air tight casing

The difference of the pressure between the inlet and the outlet of the runner is called reaction pressure, hence reaction turbine.

IMPULSE REACTION

Available energy is converted into kinetic energy

Major part of available energy is converted to pressure energy

Pressure in turbine is constant Pressure gradually reduces while water flows on the turbine blades

The wheel and the blades should have accesses to free air and must not run full

The blades are always under the action of pressure, wheel must always run full

Only one face of blade is active Both sides

Turbine must always be installed above water level in tail race

The turbine is usually set above the tailrace.

Regulation of flow and power is easier without loss of energy

Difficult

Used for high heads Low and medium heads

Efficiency is less Efficiency is more

Energy transfer being change in energy

Due to change in pressure head

PELTON WHEEL OR PELTON TURBINE

Runner consists of circular disk with a suitable number of double hemi ellipsoidal cups know as buckets evenly spaced round its periphery

One or more nozzles are mounted to direct a jet of water on the runner in tangential direction

The nozzle is fitted with a spear or needle fixed to the end of a rod

The impulse force produced due to this momentum of water causes the turbine to rotate

The double semi ellipsoidal buckets split the water jet in two half’s which helps in balancing the turbine.

FRANCIS TURBINE

Francis turbine is a radial inward flow turbine and is the most popularly used one in the medium head range of 60 to 300 m.

The main components are (i) The spiral casing (ii) Guide vanes (iii) Runner (iv) Draft tube

The spiral casing surrounds the runner completely Its area of cross section decreases gradually around the

circumference. This leads to uniform distribution of water all along the

circumference of the runner. A draft tube is a large pipe with increasing cross section

area which connects the runner exit to the tailrace

Water enters the runner through the guide blades along the circumference

The blade passages act as a nozzle in this aspect guiding the water at the proper direction

The area of blade passage is changed to vary the flow rate of water according to the load so that the speed can be maintained constant

The runner is circular disc and has the blades fixed on one side. In high speed runners in which the blades are longer a circular band may be used around the blades to keep them in position.

The runners change the direction and magnitude of the fluid velocity and in this process absorb the momentum from the fluid.

GUIDE VANES (YELLOW) AT MINIMUM FLOW LOW SETTING

CUT-WAY VIEW OF FRANCIS TURBINE :-

Kaplan Turbine

KAPLAN TURBINE

Main components are1. Runner with runner blades2. Scroll casing3. Guide vanes4. Draft tube

It is an axial flow turbine Suitable for low head and large quantity of water The inlet is trough the scroll casing which is in the form of the

spiral After entering in to the casing water gets distributed into the

guide vanes In guide vanes water turns through a right angle into axial

direction

Water flows over the runner blades and losses their pressure energy to impart kinetic energy to the runner

Runner blades as well as guide vanes are adjustable Finally water is discharged to the tail race through a

gradually expanding tube called the draft tube

HYDRAULIC MACHINERY