Two-phase heat transfer characteristics for R-22/R-407C in a 6.5-mm smooth tube

Two-phase friction and heat transfer characteristics for R-22/R-407C inside a 6.5-mm smooth tube are reported in this study. The heat transfer results for G=100 and 400 kg/m² s were reported in the present study, and the adiabatic frictional pressure drop was recorded in the range of 100 to 700 kg/m² s. It is found that the development of flow pattern for R-407C falls behind R-22. This may explain the lower pressure drops for R-407C. The major heat transfer mechanism at low mass flux is nucleate boiling, and virtually becomes the convective evaporation as mass flux increase to G=400 krg/m² s, Meanwhile, the reduction of heat transfer coefficients for R-407C mixtures are especially profound at low mass flux, and the reduction of heat transfer coefficient decreases with the increase of mass flux.