TY - JOUR
TI - Detailed analysis of the effect of the turbine and compressor isentropic efficiency on the thermal and exergy efficiency of a Brayton cycle
AU - Živić Marija
AU - Galović Antun
AU - Virag Zdravko
JN - Thermal Science
PY - 2014
VL - 18
IS - 3
SP - 843
EP - 852
PT - Article
AB - Energy and exergy analysis of a Brayton cycle with an ideal gas is given. The  irreversibility of the adiabatic processes in turbine and compressor is taken  into account through their isentropic efficiencies. The net work per cycle,  the thermal efficiency and the two exergy efficiencies are expressed as  functions of the four dimensionless variables: the isentropic efficiencies of  turbine and compressor, the pressure ratio, and the temperature ratio. It is  shown that the maximal values of the net work per cycle, the thermal and the  exergy efficiency are achieved when the isentropic efficiencies and  temperature ratio are as high as possible, while the different values of  pressure ratio that maximize the net work per cycle, the thermal and the  exergy efficiencies exist. These pressure ratios increase with the increase  of the temperature ratio and the isentropic efficiency of compressor and  turbine. The increase of the turbine isentropic efficiency has a greater  impact on the increase of the net work per cycle and the thermal efficiency  of a Brayton cycle than the same increase of compressor isentropic  efficiency. Finally, two goal functions are proposed for thermodynamic  optimization of a Brayton cycle for given values of the temperature ratio and  the compressor and turbine isentropic efficiencies. The first maximizes the  sum of the net work per cycle and thermal efficiency while the second the net  work per cycle and exergy efficiency. In both cases the optimal pressure  ratio is closer to the pressure ratio that maximizes the net work per cycle.