Flow Boiling of Refrigerant-Oil Mixtures in Plain and Enhanced Tubes

Research on heat transfer to refrigerants has gained importance in the 1990’s in response to the massive conversion of the refrigeration and air-conditioning industry from refrigerants ‘retired’ by the Montreal protocol (R-11, R-12, R-502, etc.) to more environmentally-safe refrigerants (R-134a, R-123, R-407C, R-410A, ammonia, hydrocarbons, etc.). Lubricating oil from these systems’ compressors, absorbed by the refrigerant charge circulating in these systems, can have a dramatic effect on boiling performance and represents one of the old, unresolved problems of refrigeration heat transfer. The present survey presents a summary of the recent research on evaporation of refrigerant-oil mixtures inside plain and microfin tubes, including experimental studies and new prediction models.