Experimental Research on Internal Working Process of Rotary Vane Expander in CO_2 Refrigeration System

A rotary vane expander was developed to replace the throttling valve to improve the coefficient of performance of the transcritical CO2 refrigeration cycle.A diagram of pressure variation with rotation angle(p-θ diagram) was recorded with two pressure sensors arranged in the expansion chamber in different angle positions.The internal thermodynamic process was analysed by means of the p-θ diagrams.The experimental results show that the rotary vane expander can work continuously and steadily while the serious internal leakage results in more rapid decrease in pressure during expansion than expected,leading to an unfavorable over-expansion.Arranging springs beneath the vanes can improve the expansion process by keeping a tight contact between the vane and the cylinder wall.A seal arranged between the inlet and outlet ports can increase the pressure difference through the expander by reducing the leakage directly from the high-pressure suction chamber to the low-pressure discharge chamber.The adiabatic efficiency is estimated to be about 20 percent and changes little with the rotation speed.