A review on expanders and their performance in vapour compression refrigeration systems

This paper reviews progress reported in the open literature of the use of expanders to recover expansion power to improve the energy efficiency of vapour compression refrigeration systems. Pioneering works in the field are first discussed, and then a variety of expander mechanisms, including reciprocating piston, rolling piston, rotary vane, scroll, screw and turbine are reviewed together with their reported performance. Most of the reported works have been for transcritical CO2 refrigeration systems, which have reported improvements in the coefficient of performance (COP) of up to 30%. In a non-CO2 system, the maximum reported increase in the COP was 10%. The maximum reported expander efficiency (i.e. the ratio of measured power to the power available if the expansion process is isentropic) was 83%, obtained with a scroll expander in a CO2 refrigeration cycle. Other expander issues including heat transfer, expansion process, internal leakage, irreversibility, control strategy, installation issues and economic analysis are also reviewed. It is noted that there are very limited studies in these areas. Finally, challenges and recommendations for future studies in the area of refrigeration expander technology were presented.