The effect of oil on the two-phase critical flow of Refrigerant 134a through short tube orifices

Abstract

An experimental investigation of two-phase flow of mixtures of Refrigerant 134a with 168 SUS polyalkylene glycol (PAG) oil through short tube orifices was performed for oil concentrations ranging from 0 to 5.1%. Both two-phase and subcooled liquid flow entering short tubes were studied for an upstream pressure of 1172 kPa, for subcoolings as high as 13.9 C, and for qualities as high as 8% at the inlet of the short tube. Downstream pressures were varied from saturation pressure, P sat ,to 310 kPa. The effects of the lubricant on the flow characteristics were discussed as a function of downstream pressure, upstream subcooling/quality and upstream pressure. The effects of oil concentration on mass flow through short tubes varied as a function of upstream subcooling or quality. The maximum reduction in flow occurred at zero subcooling, where the flow was reduced by approximately 12.1% for a 5.1% oil concentration. For entering subcooling above 8.3 C and at a quality of 5%. there were small increases in flow for the addition of oil to the refrigerant. The observed flow trends were analyzed using pressure profile measurements and visualization tests.