Simulation analysis of a two-rolling piston expander replacing a throttling valve in a refrigeration and heat pump system

An expander is used to replace a throttling valve in a refrigeration and heat pump system in order to improve the system efficiency by recovering partial expansion work. Owing to the large expansion ratios of low pressure refrigerants, a two rolling piston expander was proposed and designed. The efficiency analysis was developed by analyzing energy losses of the expander in the expansion work process. The simulation results show that the friction losses of the designed expander are about 78.5% of total losses, which influences the efficiency of expander significantly. Then the measures of reducing friction losses are presented. A theoretical expander efficiency of 72.0% is expected to be attained. •A two-rolling piston expander is designed for replacing a throttling valve of low pressure refrigerant heat pump system.•Expander energy losses analysis is carried out.•The friction losses are the main factor influencing expander efficiency.•Efficient improvement measures are discussed to improve expander efficiency.