Thermodynamic Evaluation of First and Second Law Performance of Evaporative Cooling Schemes for Regenerative Gas Turbines

Abstract

In this study, effect of evaporative cooling on performance of regenerative gas turbine cycle is investigated considering simple regenerative cycle and regenerative cycle with intercooling and reheating. Evaporative cooling is applied to inlet air in simple regenerative cycle while it is applied to compressor inlet air and air between the compressor stages in reheat regenerative cycle. The first and second law performances of the cycles incorporating evaporative cooling are compared to the corresponding conventional cycles. Effects of the temperature and relative humidity of the ambient air, the turbine inlet temperature, and the pressure ratio on the net work, the thermal efficiency, and the second-law efficiency of the cycles are investigated. It appears that evaporative cooling increases thermal efficiency, net work, and optimum pressure ratio. With respect to simple regenerative cycle at a turbine inlet temperature of 1400 K and at a pressure ratio of 20, the thermal efficiency and the net work increase by 1.5 percent and 4 percent, respectively by inlet cooling in simple regenerative cycle while they increase by 18.3 percent and 12.2 percent, respectively by inlet cooling and intercooling in reheat regenerative cycle. With respect to conventional regenerative cycle with intercooling and reheating, evaporative cooling applied to inlet air and for intercooling provides essentially no increase in thermal and second-law efficiencies while it increases the net work 8.2 percent to 17.8 percent depending on the ambient conditions. Increasing turbine inlet temperature gives a linear increase in the optimum pressure ratio. As the ambient temperature increases and the relative humidity decreases, evaporative cooling becomes more effective in improving cycle performance.