Effect of wettability on nucleate pool boiling heat transfer of a low surface tension fluid outside horizontal finned tubes

摘要

Nucleate pool boiling heat transfer of a low surface tension fluid (R134a) is tested outside the surfaces with polymer coating. Nanoscale Parylene films are coated on the surfaces with Plasma Enhanced Chemical Vapor Deposition(PECVD) method. The thickness of the coating is about 10 nm. Heat flow rate intensity varies in the scope of 15-150 kW/m~2. Saturation temperatures are 6,10 and 16 °C, respectively. According the investigation, for the smooth tube, it is found that the roughness of the surface reduced after the coating and the pool boiling heat transfer performance is also deteriorated. The boiling heat transfer can be enhanced to a certain degree for two finned structures. For the saw-teeth tube, the heat transfer coefficient(HTC) can be 1.1-1.3 times higher than that without coating. For the reentrant cavity tube, at lower heat flux, the effect of coating on the performance is insignificant. While, the heat transfer can be enhanced up to a factor of 1.2 at higher heat flux. In general, the effect of the Parylene polymer coating on the pool boiling of the low surface tension fluid R134a are insignificant at the moderate heat flux.