THE LOCAL HEAT TRANSFER COEFFICIENT AT THE BOILING OF THE ISOBUTANE/ MINERAL OIL SOLUTION FLOW IN THE PIPE

Abstract

Experimental data for refrigerant R600a mixed with the compressor mineral naphthenic oil ISO VG 15 boiling in the smooth small-diameter (5.4 mm) tube are reported. The tests were conducted at the inlet pressure psuc in the range from 62.3 to 82.2 kPa, heat flux from 2754 to 4105 W/m2, mass velocity varied between 11.90 to 18.54 kg/(m2∙s) and oil concentrations at the inlet to the evaporator from 0.25 to 0.5 % by mass. The results of the research of the local heat transfer coefficient at the boiling of the isobutane/compressor oil solution flow are given in the paper. It is shown that the substantial reduction of heat transfer coefficient was observed at high concentrations of oil. In addition, during the boiling of the refrigerant/oil solution the heat transfer coefficient in the lower part of the pipe is decreasing with mass velocity increasing.