Impulse and reaction turbines

Impulse and Reaction Turbines

The impulse and reaction turbines are used in thermal power plants.

Impulse Turbine

Impulse turbines change the direction of flow of a high velocity fluid or gas jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. There is no pressure change of the fluid or gas in the turbine blades (the moving blades), as in the case of a steam or gas turbine, all the pressure drop takes place in the stationary blades (the nozzles). Before reaching the turbine, the fluid’s pressure head is changed to velocity head by accelerating the fluid with a nozzle.

 Pelton wheels and de Laval turbines use this process exclusively. Impulse turbines do not require a pressure casement around the rotor since the fluid jet is created by the nozzle prior to reaching the blades on the rotor. Newton’s second law describes the transfer of energy for impulse turbines. Impulse turbines are most efficient for use in cases where the flow is low and the inlet pressure is high.

impulse turbine
impulse turbine

Reaction Turbines

Reaction turbines develop torque by reacting to the gas or fluid’s pressure or mass. The pressure of the gas or fluid changes as it passes through the turbine rotor blades. A pressure casement is needed to contain the working fluid as it acts on the turbine stage(s) or the turbine must be fully immersed in the fluid flow (such as with wind turbines). The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. Francis turbines and most steam turbines use this concept. For compressible working fluids, multiple turbine stages are usually used to harness the expanding gas efficiently. Newton’s third law describes the transfer of energy for reaction turbines. Reaction turbines are better suited to higher flow velocities or applications where the fluid head (upstream pressure) is low.

Reaction turbine
Reaction turbine

Difference Between Impulse and Reaction Turbines:

ParametersImpulse TurbineReaction Turbine
EfficiencyFor the same flow rate & operating condition the efficiency of impulse turbine is very lowFor same flow rate & operating condition the efficiency of the reaction turbine is high
Space RequirementThe size of impulse turbine is very less.The footprint required for reaction turbine is high
CostThe Cost of impulse turbine is much lower when compare to reaction turbine for same power rating.Reaction turbine cost is much higher due to the critical shape of rotor
ApplicationWidely used in petrochemical and refineries.Widely used in Power plants.
StagingIn the case of multistage impulse turbine, three type of compounding in impulse turbine. They are1. Pressure Compounding2. Velocity Compounding3. Pressure – Velocity Compounding No compounding is available
MaintenanceEasy MaintenanceNot so easy when compare with impulse turbine

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