Efficiency of Gas Turbine

Efficiency of Gas Turbine is defined as the ratio of workdone due to adiabatic expansion to the workdone due to isentropic expansion. In Fig. 5.17 (a) and (b), the cycle 1-2-3-4 represents the ideal cycle and 1'-2-3'-4 represents the actual cycle of a closed cycle gas turbine, in which the curve 4-1' shows the isentropic compression of air in the compressor and the curve 2-3' shows the isentropic expansion of air in the turbine. The turbine efficiency (also called adiabatic efficiency of turbine) is given by

 

The compressor efficiency (also called isentropic efficiency of compressor) is the ratio of workdone due to isentropic compression to workdone due to adiabatic compression. Mathematically, compressor efficiency,

 

Note: The efficiency of a simple gas turbine can be increased by using the following methods.

1. By compressing the air in two stages with an intercooler between the two.

2. By expanding the hot air in two stages with a reheater between the two.

3. By providing a heat exchanger through which hot gases from the turbine are made to pass which heat up the compressed air before entering the combustion chamber.