Thermal and Exergy Analysis of Brayton Cycle under Varying Temperature and Pressure Ratio

Abstract

Following increasing demand in energy consumption, there is a need to continue to study energy generation systems with a view to determining a system that will have better performance at low cost. In this study, a computer-based model was developed to analyze the thermal (first law) and exergy (second law) efficiencies of Brayton cycle. The operating parameters that were considered pressure ratio (6-16), compressor inlet temperature (270 – 340 °C) and turbine inlet temperature (1200 – 1550°C). Brayton cycle under ideal condition and conditions with a regenerator, reheater and intercooler were separately examined. The thermal efficiency of the cycle approaches 30% and the second law efficiency of the actual cycle approaches 65% as compressor inlet temperature decreases, turbine inlet temperature increases and pressure ratio approaches 10. Through the introduction of regenerator with the conditions stated earlier constant except pressure ratio approaches 6, thermal efficiency and second law efficiency was observed to approach 40% and 100% respectively. With further addition of intercooler and reheater to the system, the range of variation of the thermal efficiency and the second law efficiency was reduced while the upper limit was still kept at 40% and 100% respectively. The study concluded that it is imperative for new and improved materials to be developed to withstand high temperatures in the turbine in order to increase the thermal and exergy efficiency of the system.