Pool boiling of iso-butane and quasi azeotropic refrigerant mixture on coated surfaces

An experimental study was carried out to investigate saturated pool boiling of iso-butane and quasi-azeotropic mixture (R-600a and R-410A) for four horizontal copper surfaces fabricated by flame spraying technique. The copper powder was used as a coating material applied to the outer surface of copper tube. Boiling experiments were performed on 25.4 mm diameter copper tubes with the active length of 116 mm. Data were taken over a heat flux range of 5-50 kW m−2 and saturation temperature of 10 °C. The effects of heat flux and coating parameters (coating thickness, pore diameter and porosity) on nucleate boiling heat transfer coefficient of both refrigerants are thoroughly compared. The boiling heat transfer coefficient of copper coated surface was enhanced approximately 1.1-2 times that of plain surface. The experimental heat transfer coefficients were also compared with some existing correlations and the results of other authors published data. An empirical correlation was also developed to predict the heat transfer coefficient of both refrigerants during pool boiling over coated surfaces.