An Experimental Investigation on Flow Characteristics of Refrigeration/Oil Mixture in Vertical Upward Flow

Oil return from the evaporator to the compressor suction port is an important requirement. It is affected by the refrigerant/lubricant properties, gas velocities and piping geometry. The refrigerant R -134a has successfully replaced R-12 in household refrigerators and freezers. This paper describes a test method to estimate the mean oil film thickness and to observe the flow pattern in vertical upward flow in a R -134a suction line. The test facility to investigate a wide range of refrigerant and oil flow rates had been built. Three kinds of oils (mineral, two alkylbenzenes) have been tested with R-134a in this facility. The results show an upward net oil flow for all oils investigated regardless of the miscibility between refrigerant and oil. The refrigerant and oil mixture flow as either chum flow or annular flow in the vertical upward suction line of the refrigeration system. The mean oil thickness and flow patterns are summarized for each case.