3494 (RP-630) -- In-Tube Evaporation and Condensation of Refrigerant-Lubricant Mixtures of HFC-134a and CFC-12 PDF

In-tube heat transfer coefficients and pressure drops were experimentally determined for evaporation and condensation of HFC134a and CFC12. These measurements were performed for refrigerant-lubricant mixtures ranging from 0% to 5.4% lubricant concentrations. For HFC134a, the lubricant was a 165 SUS polyalkylene glycol (PAG), while for CFC12, the lubricant was 150 SUS naphthenic oil. Evaporation tests were performed at 5 deg C (41 deg F) and condensation tests at 40 deg C (104 deg F) over a mass flux range of 130 kg/m2.s (95,860 lb/ft2.h) to 400 kg/m2.s (294,000 lb/ft2.h). The tests were conducted in a 3.67m (12 ft) long smooth tube with an inside diameter of 8.0mm (0.31 in.). The evaporation heat transfer coefficients for HFC134a and CFC12 were increased at lubricant concentrations of 1.2% and 2.5% but were significantly decreased at lubricant concentrations of 5.3%. The evaporation pressure drops steadily increased as the lubricant concentrations were increased, with about a 50% to 100% increase in pressure drop at a 5.3% lubricant concentration. Generally, condensation heat transfer coefficients for both refrigerants were decreased with the addition of lubricant. The condensation pressure drops were increased for HFC134a by about 40% at 5.3% lubricant, but CFC12 showed no significant increases.

KEYWORDS: evaporation, condensation, heat transfer coefficient, refrigerants, mixtures, lubricants, R134a, R12, pressure drop, testing