The effects of the parameters of a refrigeration system working with R600a on the non-equilibrium subcooled two-phase flow of the refrigerant

Abstract

Abstract Household refrigerators built with vapor compression refrigeration systems use capillary tubes as expansion devices because of their low cost and simple structure. To prevent decreasing mass flow of the refrigerant and ensure the stability of the system, the refrigeration system is designed so that the refrigerant enters the capillary tube in a subcooled liquid state rather than a saturated two-phase state. However, previous researchers have reported that a two-phase flow entered the capillary in a refrigeration system running with R600a even though the refrigerant was under the subcooled temperature condition. The observed two-phase flow was in a thermodynamic non-equilibrium state, which is a mixture of subcooled liquid and subcooled vapor. Experiments were performed to investigate the effects of the refrigeration system's operating conditions on the contents of the non-equilibrium vapor phase of R600a. Experimental results demonstrated that the void fraction was changed by the system parameters in addition to the pressure and temperature. The void fraction of the non-equilibrium R600a two-phase mixture at the condenser outlet was reduced with increases in degree of subcooling, refrigerant mass flow rate, flow resistance of capillary tube, and decrease in thermal resistance on the secondary side of the condenser. The parameter that caused the biggest change in void fraction was the flow resistance of capillary tube (which was changed by a metering valve in front of capillary tube) while the effects of changes in pressure and refrigerant charge were small.