Two-phase flow boiling heat transfer of R-22 and R-410A in horizontal microchannels

Two-phase flow boiling heat transfer characteristics of R-22 and R-410A in horizontal small tubes was observed in this study. Heat flux over range of 10 to 40 kW m^-2 was conducted to the test sections, which were made of stainless steel tube with inner tube diameters of 0.3, 0.5, 1.5 and 3.0 mm, and lengths of 0.27, 0.33, 1.5 and 3.0 m, respectively, to obtain the local heat transfer coefficients. Mass flux ran under range of 70 to 600 kg m^-2 s^-1, saturation temperature under range of 2 to 12°C, and quality under up to 1.0. The section was heated uniformly by applying an electric current to the tube directly. The effects of mass flux, heat flux, inner tube diameter and saturation temperature on heat transfer coefficient were presented. The heat transfer coefficients of the present study were compared using several existing heat transfer coefficient correlations. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in small tubes, with considering the laminar flow, was developed.