Question

The pressure ratio of a power plant operating according to the ideal brayton cycle is 8. Gas temperature 300K at compressor inlet, at the entrance of the turbine is 1300K. Using air standard acceptance and taking into account the change of specific temperatures with temperature,
a.) Calculate the temperature of the gas at the compressor and turbine outlet.
b.) Calculate the thermal efficiency of the cycle.
c.) Calculate the backward work rate.

Answer 1

Solution-

Assumption-

• Kinetic and potential energies neglected at inlet and exit of turbine , compressor
• steady state operation
• Air standard assumption taking into consideration for calculating enthalpy.

TS diagram-

Analysis-

Process 1-2 Isentropic compression-

,

Work input by compressor -

Process 2-3 Heat addition in combustion chamber at constant pressure

Process 3-4 Isentropic expansion in turbine

Work output by turbine -

Process 3-4 Heat rejection at constant pressure

Results-

A) Temp of gas at exit of compressor is 543.3 K, temp. of gas at exist of turbine is 717.7 K

B) Thermal efficiency

C) Back work ratio

Note- all calculation done using C_P= 1.005 kJ/kg for air.