On the performance improvement of an inverted Brayton Cycle using a regenerative heat and mass exchanger

Abstract

Recovery of the low-temperature waste heat for electricity generation has been gaining a significant interest. An Inverted Brayton Cycle (IBC) is often employed to convert the low-temperature waste-heat to electricity while the thermal efficiency and specific work output are poor. In this paper, a new energy recovery scheme is introduced incorporating the IBC with a Regenerative Heat and Mass Exchanger (RHME). The RHME is a heat and mass exchanger that consolidates a recuperator (for thermal efficiency improvement) and an Indirect Evaporative Cooler (for enhanced specific work). Numerical models for RHME and the IBC were judiciously developed where possible condensation in the product air channel was accounted for. The model was validated with the experimental data and the cycle was investigated for various waste-heat sources (50–150 °C). When compared to a conventional air-cooling IBC system, incorporating the current energy recovery scheme increases the thermal efficiency from 8.13% to 14.36% and specific work output from 10.38 to 12.46 kJ/kg equivalent to 76.63% and 20.1% improvements, respectively. The unprecedented performance improvement is realised from the exploitation of the regenerative and air-saturation (cooling) mechanisms for both energy recovery and cooling of the working fluid.