Evaluates the effects of lubricant on spray evaporation heat transfer performance. Tests were conducted with refrigerant R134a and triangular-pitch tube bundles made from enhanced-boiling, low-finned, and plain-surface tubes. A 340-SUS polyol-ester (POE) oil was used for the R134a testing because this lubricant is being integrated into industry for use with this refrigerant. Spray evaporation heat transfer tests were performed at oil concentrations of 1.0% and 2.5% by mass fraction of the total refrigerant/lubricant mixture. Two refrigerant supply rates were used for the R134a testing so that the effects of film-feed supply rate could be interpreted from the data. Limited testing was also conducted on R22 with an enhanced boiling surface and a plain-surface bundle. A 300-SUS alkyl-benzene oil was used for the R22 refrigerant/lubricant mixture tests. Refrigerant was sprayed onto the tube bundles with low-pressure-drop, wide-angle nozzles located directly above the bundle. Collector testing was conducted with both R134a and R22 to determine the percentage of refrigerant contacting the tube bundle. It was found that small concentrations of the polyol-ester lubricant yielded significant improvement in the heat transfer performance of R134a. The shell-side heat transfer coefficient was more dependent on lubricant concentration than on film-feed supply rate within the range of the respective parameters evaluated in this study. As expected, pure R22 results show higher heat transfer coefficients than those obtained with pure R134a at the same saturation temperature of 2.0degC (35.6degF). However, enhanced-boiling-surface bundle results showed that a 1.0% refrigerant/lubricant mixture of the POE lubricant with R134a yielded higher heat transfer coefficients than a 1.0% mixture of the alkyl-benzene lubricant with R22.

KEYWORDS: year 1996, lubricants, refrigerants, sprays, evaporation, heat flow, performance, R134a, R22, tubes, calculating, testing, oil, mixtures, heat transfer coefficient