Effect of oil on the boiling performance of structured and porous surfaces

The effect of geometric parameters and compressor oil concentration on the performance degradation of enhanced surfaces were investigated. Data are presented for innovative structured and porous surfaces. Refrigerant R-134a at 26.6°C with 1%, 2.5%, and 5% polyester-ester oil concentration by mass was used as the working fluid. Pore diameter was not found to be a major factor for the oil degradation of boiling performance on structured surfaces and that the smaller pore pitch yielded slightly greater oil degradation. Tubes with 50 fins/in (0.51 mm fin spacing) and 0.9 mm fin height had a smaller oil degradation than the Turbo-B surface. The rectangular fin base substantially enhanced the boiling performance in pure refrigerant but in the oil presence, this geometry performed poorly. The effect of oil degradation increased as the tunnel cross section area decreases. For 5% oil concentration, the porous surface had a performance degradation similar to the Turbo-B tube.