Study of Two-rotor Rolling Piston Expander Used in Trans-critical CO_2 Compression Cycle

The efficiency of CO2 refrigeration system is lower than that of traditional refrigeration systems using synthetic refrigerants.The expander can reduce energy losses in the expansion process,so the transcritical cycle with expander is adopted in order to improve the COP of the CO2 refrigeration cycle.In view of the current problems in the expander,a new two-rotor rolling piston expander used in transcritical CO2 refrigeration cycle is designed.This expander needs no special suction control equipment,whose first-stage cylinder connects with the suction pipe,and whose second-stage cylinder connects with the exhaust pipe,expansion space is formed between two cylinders.Theoretical analysis and design calculation of expander operation process are carried out to obtain the main structural parameters,and force and moment are calculated.Analytical result shows that the total moment of the first-stage rotor is always of a positive value in the expansion process and the total moment of the two rotors becomes negative when the expansion is about to end.The driving moment of the second-stage rotor is greater than that of the first-stage rotor before θ2,and after that the driving moment of the first stage rotor is greater.