Study on flow condensation characteristics of refrigerant R410a in a single rectangular micro-channel

A visualization experimental investigation on the condensation heat transfer of refrigerant R410a in a rectangular micro-channel with hydraulic diameter of 0.67 mm is conducted in this paper. Experiments are conducted with saturation temperatures of 36-41 °C, and the refrigerant mass fluxes is in the range of 109-1042 kg/(m2 s) over the entire range of vapor qualities. One-dimension annular flow model is established to study the condensation heat transfer characteristics inside micro-channel. The condensate film thickness, dimensionless condensation liquid flow velocity, local heat transfer coefficient and average heat transfer coefficient are obtained to analyze the condensation heat transfer mechanism in micro-channel. The predicted value of heat transfer coefficient has great agreement with experimental data in this study. Visualization experimental results agree with condensation flow patterns map in micro-channel proposed by other researcher. Annular flow, wavy-annular flow, slug flow and bubble flow are observed along the flow direction in micro-channel under the low mass flux. Saturation pressure, mass flux, sub-cooled and vapor quality of R410a are considered. The results show that the heat transfer coefficient increases with mass fluxes and vapor quality remarkably. Experiment results are 17% higher than other research results, especially in high mass flux and vapor quality. In addition, the significant influence of sub-cooled is proposed and discussed in micro-channel condensation study. The lower sub-cooled will bring higher heat transfer coefficient.