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
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