UNIT -IV

1.Hydraulic Turbines and pumps

2.Classification of Hydraulic Turbines

K.Balasundaram , M.E.,

Assistant Professor

Mechanical Engineering Department

K.C.G. College Of Technology

WHAT IS TURBOMACHINERY ?

“turbo” or “turbines” is Latin in origin and implies

that which spins or whirls around

A turbo machine is a rotating (as opposed to

reciprocating) device that extracts energy from or

adds energy to fluids.

Energy is transferred to or from a continuously

flowing fluid by the dynamic action of moving

blades or rotors.

TURBINES

Turbines are defined as the hydraulic machines which convert hydraulic energy into mechanical energy.

This mechanical energy is used in running an electric generator which is directly coupled to the shaft of the turbine.

Thus the mechanical energy is converted into electrical energy

PUMPES

Pumps are defined as the hydraulic machines which convert Mechanical energy into hydraulic energy are called pumps.

HYDRO-ELECTRIC POWER PLANT

Hydraulic turbines are the machines which use the energy of water and convert it to mechanical energy.

The mechanical energy developed by a turbine is used in running an electric generator which is directly coupled to the shaft of the turbine.

The electric generator thus develops electric power, which is known as hydro-electric power.

General Layout of a Hydraulic Power Plant

A dam constructed across a river to store water

Pipes of large diameters called penstocks

Turbines having different types vanes fitted to the wheel

Tail race, which is a channel which carries water away from the water

DEFINITIONS OF HEADS Gross Head: The difference between the head race level and tail race level

when no water is flowing is known as Gross head. It is denoted by Hg Net Head : It is also called effective head and is defined as the head

available at the inlet of the turbine. It is denoted by H Net Head H = Hg – hf Where Hg = Gross head hf = Head loss due to friction

24. . .

2f

f LVh

d g

CLASSIFICATION OF HYDRAULIC

TURBINES The hydraulic turbines classified are According to the type of energy at inlet

Impulse turbine and Reaction turbine

According to the direction of flow through runner Tangential flow turbine Radial flow turbine Axial flow turbine and Mixed flow turbine

According to the head at the inlet of turbine High head turbine Medium head turbine and Low head turbine

According to the specific speed of the turbine Low specific speed turbine Medium specific speed turbine and High specific speed turbine

IMPULSE TURBINE

If at the inlet of the turbine, the energy available is only kinetic energy, the turbine is known impulse turbine

Example:

Pelton wheel turbine

REACTION TURBINE

If at the inlet of the turbine,

the water possesses kinetic energy as well as

pressure energy, the turbine is known as

reaction turbine.

Example:

Francis turbine,

Kaplan turbine

RADIAL FLOW TURBINE

If the water flow in the radial direction through the runner, the turbine is called radial flow turbine

INWARD RADIAL FLOW TURBINE : If the water flows from outward to

inward, radially the turbine is known as inward radial flow turbine.

OUTWARD RADIAL FLOW TURBINE : If the water flow radially from

inward to outwards, the turbine is known as outward radial flow turbine.

AXIAL FLOW TURBINE :

If the water flow through the runner along the direction parallel to the axis of rotation of the runner, the turbine is called axial flow turbine.

MIXED FLOW TURBINE:

If the water flows through the runner in the radial direction but leaves in the direction parallel to axis of rotation of the runner, the turbine is called mixed flow turbine.

TANGENTIAL FLOW TURBINE :

If the water flows along the tangent of the runner, the turbine is known as tangential flow turbine.

Reaction (Static pressure changes)

Converts both Flow & Kinetic energy

Impulse: (Static pressure unchanged)

Converts only Kinetic energy

Tangential flow on buckets (Pelton)

Radial or (Francis turbine)

Axial flow or propeller turbine

Man-Boat Analogy

Man = Fluid Boat = Rotor blade

IMPULSE

REACTION

DIFFERENCE BETWEEN IMPULSE AND REACTION TURBINES

Sl: No:

Impulse turbine Reaction turbine

1.

2.

3.

4.

All the potential energy is converted into kinetic energy by nozzle before entering to turbine runner.

Flow regulations is possible without loss

Unit is installed above the tailrace

Blades are only in action when they are in front of nozzle.

Only a portion of the fluid energy is transferred into kinetic energy before the fluid enters the turbine

Flow regulation is possible with loss

Unit is kept entirely submerged in water below tailrace

Blades are in action at all the time

IMPULSE TURBINE If at the inlet of the turbine, the energy available is only

kinetic energy, the turbine is known impulse turbine.

Tangential flow turbine

In tangential flow turbine, water flows along the tangent

to the path of the runner.

Example:

Pelton wheel turbine

Impulse turbine (PELTON WHEEL)

Converts

kinetic energy alone

The main parts of the pelton turbine are

Nozzle and flow regulating arrangement Runner and buckets Casing and Breaking jet

Nozzle and flow Regulating Arrangement

The amount of water striking the buckets (vanes) of the runner is controlled by providing a spear in the nozzle as shown in fig. The spear is a conical needle which is operated either by a hand wheel or automatically in an axial direction depending upon the size of the unit. When the spear is pushed forward into the nozzle the amount of water striking the runner is reduced. On the other hand, if the spear is pushed back, the amount of water striking the runner increases.

Runner with Buckets Fig shows the runner of a pelton wheel. It consists of a circular disc on the periphery of which a number of buckets evenly spaced are fixed. The shape of the buckets is of a double hemispherical cup or bowl. Each bucket is divided into two symmetrical parts by a dividing wall which is known as splitter.

The jet of water strikes on the splitter. The splitter divides the jet into two equal parts and the comes out at the outer edge of the bucket. The buckets are shaped in such a way that the jet gets deflected through 1600 or 1700. The buckets are made of cast iron, cast steel bronze or stainless steel depending upon the head at the inlet of the turbine.

Casing The function of the casing is to prevent the splashing of the

water and to discharge water to tail race. It also acts as safeguard against accidents. It is made of cast iron or fabricated steel plates. The casing of the pelton wheel does not perform any hydraulic function.

Breaking jet When the nozzle is completely closed by moving the spear in

the forward direction the amount of water striking the runner reduces to zero. But the runner due to inertia goes on revolving for

a long time. To stop the runner in a short time, a small nozzle is provided which directs the jet of water on the back of the vanes.

This jet of water is called breaking jet.

VELOCITY TRIANGLES AND WORK

DONE FOR PELTON WHEEL Fig shows the shape of the buckets of the

pelton wheel. The set of water from the nozzle strikes the bucket at the splitter which splits up the set into two parts. These part of the set, glides over the inner surfaces and comes out at the outer edge.

The inlet velocity triangle is drawn at the splitter and outlet velocity triangle is drawn at the outer edge of the bucket.

RADIAL FLOW REACTION TURBINES

Reaction turbine means that the water at the inlet of the turbine possesses kinetic energy as well as pressure energy. As the water flows through the runner, a part of pressure energy goes on changing into kinetic energy.

Thus the water through the runner is under pressure. The runner is completely enclosed in an air – tight casing and casing and the runner is always full of water.

Radial flow turbine are those turbines in which the water flows in the radial direction.

The water may flow radially from outwards to inwards or from inwards to outwards

Examples : Francis Turbine Kaplan Turbine

Propeller Turbine

Main parts of radial flow Reaction Turbine

1.Casing

2.Guide mechanism

3.Runner, and

4.Draft tube

INWARD RADIAL FLOW TURBINE

If the water flows from outwards to inwards through the

runner, the turbine is known as inward radial flow turbine

The water flows over the moving vanes in the inward radial direction and is discharged at the runner diameter of the runner. The outer diameter of the runner is the inlet and the inner diameter is the outlet.

Velocity Triangles

INWARD RADIAL FLOW TURBINE

Inlet Triangle

Outlet Triangle

Outward radial Flow reaction Turbine

The outward radial flow reaction turbine in which the water from casing enters the stationary guide wheel.

The guide wheel consists of guide vanes which direct water to enter the runner which is around the stationary guide wheel.

The water flows through the vanes of the runner in the outward radial direction and is discharge at the outer diameter of the runner.

The inner diameter of the runner is inlet and outer diameter is the outlet.

Outward radial Flow reaction Turbine

The velocity triangles at inlet and outlet will be drawn by the same procedure as inward flow turbine.

Francis turbines This is the most common turbine type in hydroelectric stations.

The Francis turbine is a radial-flow turbine with water flowing in a radial direction inward over the curved runner blades toward the centre of the turbine

Francis turbines are suitable for hydroelectric systems with water heads between 2 meters to 200 meters, and the efficiency can be over 90%.

A Francis turbine comprises mainly the four components

.

1. spiral casing,

2. guide on stay vanes,

3. runner blades and

4. draft-tube

Francis Turbine (Mixed flow)

Francis turbines

Francis turbine

Velocity Triangles of Francis turbines

The velocity triangle at inlet and outlet of the Francis turbines are drawn in the same way as incase of inward flow reaction turbine.

As in case of Francis turbine, the discharge is radial at outlet, the velocity of whirl at outletVw2 will be zero.

AXIAL FLOW REACTION TURBINE If the water parallel to the axis of the rotation of the shaft,

the turbine is known as axial flow turbine.

For the axial flow reaction turbine the shaft of the turbine is vertical. The lower end of the shaft is made larger which is known as ‘hub” or boss.

The vanes are fixed on the hub and hence acts as a runner for axial flow reaction turbine.

The following are the important type of axial flow reaction turbines

Propeller Turbine and

Kaplan Turbine

Propeller Turbine

The vanes are fixed to the hub and they are not adjustable, the runner is known as propeller turbine.

Kaplan TurbineThe vanes on the hub are adjustable the turbine is known as a Kaplan turbine. This turbine is suitable where a large quantity of water at low heads is available.

Kaplan Turbine

Kaplan turbine, which consists of a hub fixed to the shaft. On the hub, the adjustable vanes are fixed as shown in fig.

The main parts of Kaplan turbine are

Scroll casingGuide vanes mechanism

Hub with vanes or runner of the turbine , andDraft tube.

Axial flow (Kaplan) Turbine

Difference Between Francis and Kaplan Turbine

Sl;No Francis turbine Kaplan turbine

1.

2.

3.

4.

Mixed flow reaction turbine

Runner vanes are not adjustable

Medium head turbine (50m to 250m

Large No of vanes 16 to 24

Axial flow reaction turbine

Runner vanes are adjustable

Low head turbine (up to30m)

Less No of vanes 3 to 8

- Propeller Turbine

•A propeller turbine generally has a runner with three to six blades in which the water contacts all of the blades constantly.

•Picture a boat propeller running in a pipe. Through the pipe, the pressure is constant; if it isn't, the runner would be out of balance. •The pitch of the blades may be fixed or adjustable.

•The major components besides the runner are a scroll case, wicket gates, and a draft tube.

AXIAL FLOW PROPELLER TURBINE

AXIAL FLOW Propeller / Kaplan Hydraulic Turbine

Guide Vanes / Wicket Gates

Rotor w/ blades

Draft Tube / Diffuser / Casing

Kaplan Turbine = Propeller turbine with adjustable blades Efficiency 90 - 93% Cavitation a concern

Propeller Turbine

MIXED FLOW Fluid flow over the rotor is both axial and radial

Radial Inflow / Axial Outflow ….. MIXED FLOW Reaction Turbine Common in large hydraulic power plants Large Flow / Medium Head / Low Specific Speed

EFFICIENCIES OF A TURBINE

The following are the important efficiencies of a turbine

1 .Hydraulic efficiency

2 . Mechanical efficiency

3 . Volumetric efficiency

4 . Overall efficiency

Hydraulic efficiency

If is defined as the ratio of power given by water to the runner of a turbine to the power supplied by the water at the inlet of the turbine

Power deliverd to runner

Power supplied at inlet

Mechanical efficiency If is defined the ratio of the power available at the shaft of the turbine to the power delivered to the runner.

Power at the shaft of the turbine

Power delivered by water to the runner

Volumetric efficiency If is defined the ratio of the volume of the water actually striking the runner to the volume of water supplied to the turbine.

OVERALL EFFICIENCY

If is defined as the ratio of power available at the shaft of the turbine to the power supplied by the water at the inlet of the turbine.

Volume available at theshaft of the turbine

Power supplied at the inlet of the turbine

specific speed It is defined as the speed of a turbine which is identical in shape, geometrical

dimensions, blades angles, gate opening etc., with the actual turbine but of such a size it will develop unit power when working under unit head. It is denoted by the symbol Ns

The specific speed is used in comparing the different types of turbines as every type of turbine has different specific speed.

Where N= Speed of actual turbine

P = Power developed

H = head under which the turbine is working

5/4= s

N PN

H

Significance of specific speed

Specific speed plays an important role for selecting the type of the turbine. Also the performance of a turbine can be predicted by knowing the specific speed of the turbine.

The type of turbine for different specific speed is given in Table 18.1 as:

S.No.

Specific speed Types of turbine

(M.K.S.) (S.I.)

1.

2.

3.

4.

10 to 35

35 to 60

60 to 300

300 to 1000

8.5 to 30

30 to 51

51 to 225

225 to 860

Pelt on wheel with single jet

Pelton wheel with two or more jet

Francis turbine

Kaplan or propeller turbine

Turbine application

Head (pressure)

Turbine High Medium Low

(30m +) (<10 m)

Impulse Pelton Cross flow Cross flow Turgo Pelton

Turgo

Reaction - Francis Propeller

Pump Darius 19