Subject : Power Plant Engineering

Topic: Chap 4- Combined Cycles

Difficulty: Medium

Pressure ratio: It is the ratio of cycle’s highest to its lowest pressure, usually highest pressure-compressor discharges to the lowest-pressure-compressor inlet pressures.

Work ratio: It is the ratio of network output to the total work developed in the turbine or turbines.

Air ratio: Kg of air entering the compressor inlet per unit of cycle net output, for example, kg/kWh.

Compression efficiency: It is the ratio of work needed for ideal air compression through a given pressure range to work actually used by the compressor.

Engine efficiency: It is the ratio of work actually developed by the turbine expanding hot power gas through a given pressure range to that would be yielded for ideal expansion conditions.

Machine efficiency: It is the collective term meaning both engine efficiency and compressor efficiency of turbine and compressor efficiency of turbine and compressor, respectively.

Combustion efficiency: It is the ratio of heat actually released by 1 kg of fuel to heat that would be released by complete perfect combustion.

Thermal efficiency: It is the percentage of total energy input appearing as net work output of the cycle.