Convective condensation of R600a, R290, R1270 and their zeotropic binary mixtures in horizontal tubes

The present paper concerns an experimental investigation about the heat transfer coefficient during convective condensation of hydrocarbons and their zeotropic mixtures. Experiments were performed in a horizontal smooth channel, with internal diameter of 9.43 mm for R600a, R290, R1270, R600a/R290 (70/30 molar fraction) and R600a/R1270 (75/25 molar fraction), for mass velocities ranging from 50 to 250 kg m−2 s−1, vapor qualities from unity to zero, heat fluxes from 5 to 60 kW m−2 and a saturation temperature of 35°C. Experiments were also performed for R134a. In general, higher heat transfer coefficients were obtained for the hydrocarbons compared to R134a. The heat transfer process was dominated by shear effects for the hydrocarbons regardless of the mass velocity. At low mass velocities (below 100 kg m−2 s−1), both mixtures provided lower heat transfer coefficients than the pure fluids. At high mass velocities a reduction of the heat transfer coefficient compared to the pure fluid was noticed only for R600a/R1270 at high qualities. The experimental data is compared against prediction methods from literature and based on the pure fluids database, a new strictly empirical prediction method is proposed, which performs better for both pure fluids and mixtures database. For the mixtures, the performance of the methods was improved when considering a correction for the mass transfer effects associated to the concentration gradients near the liquid/vapor interface.