Experimental investigation on a turbo expander substituted for throttle valve in the subcritical refrigeration system

Owing to the large volumetric expansion ratio of the subcritical refrigerant and the geometrical restriction of the positive displacement machine, investigations on expanders in subcritical vapor refrigeration systems are relatively few in the literature. In this paper, a radial inflow turbo expander prototype is developed for expansion power recovery in the subcritical refrigeration system. The experimental results show that the prototype can operate stably within a wide speed range of up to 3200 rpm. A maximum of 10.4% isentropic efficiency is obtained when the inlet pressure is 1.7 MPa. It is also found that the optimum velocity ratio of the expander is 0.08-0.14 and shifts to higher values with the increase of the expander inlet pressure. Also, the defects of the prototype are discussed to further improve its performance.