EFFECT OF LUBRICATING OIL ON FLOW BOILING HEAT TRANSFER OF PROPANE IN EXTRUDED MULTI-PORT TUBES

The effects of lubricating oil on flow boiling of the natural refrigerant propane (R290) in mini-channel multiport tubes with 18 paths of square cross section (0.9 mm x 0.9 mm) were experimentally investigated. In the experiments, the local heat transfer coefficients and pressure drops were measured using a mini-channel multiport tube made of aluminum. The experiments were conducted over a range of oil circulation rates from 0 to 5 wt%, inlet vapor quality of 0 to 0.25, mass flux of 25 to 70 kgm(-2)s(-1), heat flux of 3 to 8 kWm(-2), and evaporation temperature of 15 degrees C. Polyolester oil, which is miscible with the refrigerant, was used. When the heat flux is small, the heat transfer coefficient tends to decrease almost uniformly as the oil concentration increases, whereas when the heat flux is large, the heat transfer coefficient increases by the addition of oil. We also report on the relationship between oil concentration rate and pressure drops and the comparison between R290 and refrigerant R32.