Previous work performed on the evaporation and condensation of refrigerant-oil mixtures has been extended to cover mixtures of a more viscous oil in a smooth tube and a micro-fin tube. The refrigerant was R-22 and the oil was a 300 SUS naphthenic mineral oil, while the previous study used 150 SUS oil. The test section, which was heated or cooled by water flowing in a surrounding annulus, was a straight, horizontal tube with an outside diameter of 0.375 in (9.52 mm) and a length of 12 ft (3.67 m). Nominal test conditions were 37°F (3°C) during evaporation and 105°F (41°C) during condensation. Mass fluxes were varied from 92,000 to 294,000 lb/h • ft² (125-400 kg/m² • s) and the oil concentration was varied from 0% to 5% by weight. For both evaporation and condensation, the vapor quality change was between 15% and 85%.

Unlike tests with 150 SUS oil, in which heat transfer was enhanced by more than 30% in some cases, there was no significant enhancement of evaporative heat transfer with 300 SUS oil. In general, the heat transfer was degraded in both tubes, with the greatest observed degradation at the maximum oil concentration of 5%. The maximum decrease was about 30% for the micro-fin tube and about 20% with the smooth tube. Condensation tests with 300 SUS ofl produced results very similar to earlier tests with 150 SUS oil, with heat transfer always decreasing as off concentration increased. The percentage decrease in heat transfer was similar for both tubes. At 5% oil concentration, the decrease r~nged from about 10% with the smooth tube to 20% with the micro-fin tube.