A hybrid power cycle using an inverted Brayton cycle with an indirect evaporative device for waste-heat recovery

The inverted Brayton cycle can be applied to exploit the exergy content of the waste heat. The cycle can be operational at low heat source temperatures, and it is particularly suitable for recovering the low-temperature waste heat. Being low temperature-driven, the thermal efficiency of such an inverted Brayton cycle is considerably low. In this study, an attempt has been made to improve the performance of the cycle by hybridizing with an indirect evaporative cooling (IEC) device. A counter-flow type indirect evaporative cooler is introduced to the inverted Brayton cycle to condition the working fluid prior to the compressor inlet. Detailed numerical models for both cycles were developed and validated with the experimental data of Riangvilaikul and Kumar for a counter flow IEC. The performance of the present configuration is compared with various methods of cooling the working fluid such as the conventional air cooling and a recuperator. The proposed cycle exhibits a significant improvement in terms of the specific work output (45%) for all turbine inlet temperatures regardless of the inlet air conditions, while a higher thermal efficiency can be realized for low-temperature heat source below 85 °C.