The device which converts hydraulic energy into mechanical energy is known as Hydraulic Machines. The hydraulic machine which converts the hydraulic energy into mechanical energy is known as turbine.
The hydraulic turbine is a mechanical device that converts the potential energy contained in an elevated body of water (a river or reservoir) into rotational mechanical energy.
History of Turbine :
The hydraulic turbine has a long period of development, its oldest and simplest form being the waterwheel, first used in ancient Greece and subsequently adopted throughout medieval Europe for the grinding of grain, etc.
A French engineer, Benoit Fourneyron, developed the first commercially successful hydraulic turbine (circa 1830). Later Fourneyron built turbines for industrial purposes that achieved a speed of 2300 rev/min, developing about 50 kW at an efficiency of over 80%.
The American engineer James B. Francis designed the first radial-inflow hydraulic turbine that became widely used, gave excellent results, and was highly regarded. In its original form it was used for heads of between 10 and 100 m.
The Pelton wheel turbine, named after its American inventor, Lester A. Pelton, was brought into use in the second half of the nineteenth century. This is an impulse turbine in which water is piped at high pressure to a nozzle where it expands completely to atmospheric pressure. The emerging jet impacts onto the blades (or buckets) of the turbine, which produce the required torque and power output. The increasing need for more power during the early years of the twentieth century also led to the invention of a turbine suitable for small heads of water, i.e., 3 to 9 m, in river locations where adam could be built.
In 1913 Viktor Kaplan revealed his idea of the propeller (or Kaplan) turbine, see which acts like a ship’s propeller but in reverse. At a later date Kaplan improved his turbine by means of swiveling blades, which improved the efficiency of the turbine appropriate to the available flow rate and head.
CLASSIFICATION OF TURBINES :
1) According to the type of energy at Inlet :
a) Impulse turbine
The impulse turbine is called De Laval Turbine since it was invented by Dr Gust of De Laval and patented by him in 1888.
The turbine which takes a high pressure and high enthalpy steam, expands it in fixed nozzles and then uses the rate of change of angular momentum of the fluids in a rotating passage to provide the torque to the rotor is called impulse turbine.
Construction : The main parts of the impulse turbine include rotor nozzles blades and casing. The casing forms the outer cover of the turbine and the nozzles are fixed in it. The moving blades are fixed on the rotating element known as rotor. The rotor is coupled with the shaft of the turbine from which the useful torque is obtained.
The impulse turbine is based on two principle :
- It requires nozzle so that pressure drop of steam takes place in the nozzles. The steam enters the turbine with a high velocity. The pressure in the turbine remains constant because whole of the pressure drop take place in the nozzles.
- The velocity of the steam is reduced as some of the kinetic energy in the steam is used in producing work on the turbine shaft.
b) Reaction Turbine
A turbine in which the steam pressure decreases gradually while expanding through the moving blades as well as passing through the fixed blades or nozzles is called reaction turbine
Construction : It consists of rows of moving blades mounted on a drum. These moving blades are separated by rows of fixed blades mounted in the casing.
2) According to the direction of flow through runner :
a) Tangential flow turbine
Water turbines of this type receive high-pressure water from single or multiple jets that either point at a tangent to the runner along the centre line, or point at the side of the runner near the periphery. In each case the water must meet the bucket inlet with as little ‘shock’ as possible and discharge tangentially with an equal and opposite velocity so that the water falls to the bottom of the casing having extracted as much energy as possible.
b) Radial flow turbine
The radial flow turbine is used in turbocharges which is mainly used in small automotive or truck The radial flow turbine is similar in appearance to the centrifugal compressor, but with the flow in the inward direction and nozzle vanes replacing the diffuser vanes.
c) Axial flow turbine
The axial type is commonly used for the large turbochargers applied to medium-speed stationary and railway traction engines and large marine engines.
Each blade on these axial flow impellers is pitched at a 45 degree angle, providing a surface for the liquid to move across to create a localized shear area. Axial flow turbines draw more power per volume than a propeller or hydrofoils as motor power is converted to shear energy.
d) Mixed flow turbine
The flow enters the turbine in a radial direction, flowing towards its axis, but after striking and interacting with the turbine blades it exits along the direction of that axis. It is for this reason that the Francis turbine is called a mixed-flow turbine.
3) According to the head at the inlet of turbine :
a) High head turbine E.g. Pelton Turbine
b) Medium head turbine E.g. Francis Turbine
c) Low head turbine E.g. Kaplan turbine
4) According to the specific speed of the turbine :
a) Low specific speed turbine :
Specific speed of such turbines will be in the range of 8 to 30 with single nozzle and up to 50 with multiple nozzles. Hence such turbines will be termed as low specific speed turbines. Pelton turbine is the best example of low specific speed turbine.
b) Medium specific speed turbine :
Specific speed of such turbines will be in the range of 50 to 250 and hence such turbines will be termed as medium specific speed turbines. Francis turbine is the best example of medium specific speed turbine.
c) High specific speed turbine :
The specific speed is more than 250.
Example: Kaplan or propeller turbine.
Hydraulic turbines are the prime movers that convert the energy of the falling water into a rotational mechanical energy and consequently to an electric energy through the use of the generators that are connected to the turbines. Turbines consist of a row of blades that are fixed on a rotating shaft or a plate. The shaft rotates because of the impact of the difference in velocity and pressure of the water striking the blades.