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Turbines• A turbine is a rotary engine that exerts energy from a fluid flow and converts it into useful work.
There are two basic types of turbines according to the mode of steam.1. Impulse turbine2. Reaction turbine
Impulse turbineWorking principle It runs by impulse of steam. Nozzle directs the steam on the curved blades, which causes them to rotate. The blades are in the shape of buckets.
The energy to rotate an impulse turbine is derived from the kinetic energy of the steam flowing through the nozzle. The potential energy is converted into kinetic energy when it passes through the nozzle. The velocity of steam is reduced when it passes over the blades.
Reaction turbineWorking principle It has no nozzle. Two rows of moveable blades are separated by one row of fixed blades. Fixed blades are attached to the casing & act as nozzles. Blades are like the wings of a plane.
Velocity of steam is increased when it passes through the fixed blades. The enthalpy drop in moving blades is called degree of reaction. A common arrangement can have 50% of enthalpy drop in moving blades, it is said to have 50% reaction. If all enthalpy drops in moving blades then it is said to be 100% reaction.
Difference between impulse andreaction turbineS.NO Impulse turbine Reaction turbine The steam flows through the The steam first flows through the 1. nozzle and impinges on the guide mechanism and then through moving blades. the moving blades. The steam impinges on the The steam glides over the moving 2. buckets with kinetic energy. vanes with pressure and kinetic energy. The steam may or may not be The steam pressure is reduced 3. admitted over the whole during its flow through the moving circumference. blades. 4. The blades are symmetrical The blades are not symmetrical
Efficiency To maximize the efficiency of steam turbine the steam is expanded, generating work in a number of stages. Multiple stages turbines are highly efficient. Most steam turbines use a mixture of both impulse and reaction design. Higher pressure sections are impulse type and lower pressure sections are reaction type.
Advantages of steam turbine It can develop higher speeds. The steam consumption is less. All the parts are enclosed in a casing so it is safe. It requires less space and lighter foundations. There is very less friction in the turbine due to few sliding parts.
Uses Turbines are used in force draft blowers, pumps and main propulsion turbines. Used in the jet engines and air crafts. They are also used in power plants , ships and submarines.
Pressure velocity graph of impulse and reaction turbines.