Oil retention and pressure drop of R1234yf and R134a with POE ISO 32 in suction lines

In most of the refrigeration systems a small quantity of oil is carried out of the compressor by high velocity vapor leaving the compressor discharge in the form of a mixture with the refrigerant. The circulating liquid which is a mixture of oil and refrigerant has the highest viscosity in the suction line to the compressor due to which it has the highest potential for oil retention. R1234yf is a new alternative refrigerant of low global warming potential (GWP) which has been developed for automobile air conditioners as a drop-in replacement for R134a in order to meet European Union???s low GWP requirement. A quantitative comparison of oil retention and pressure drop characteristics of R1234yf and R134a with POE32 oil in 10.2 mm inside diameter horizontal and vertical suction lines at saturation temperature of 13oC with 15oC of superheat is presented. The effect of pipe inclination on oil retention was also investigated. High speed videos of the flow were taken to relate flow regimes to the oil retention data. Test results show that for same system cooling capacity, R1234yf and R134a have very similar oil retention; however, the use of R1234yf results in 20-30% higher pressure drop. It was also found that inclined suction lines retain more oil than vertical lines. A semi-empirical model for prediction of oil retention and pressure drop in vertical suction lines in annular flow regime is presented. The model predicts 90% of the oil retention and pressure drop within ?? 20% and ?? 30% of the experimental data. The model is used to propose a new criterion for minimum refrigerant mass flux which could be useful as an improved guideline for sizing of vertical suction lines