INFLOW CONDENSATION HEAT TRANSFER CHARACTERISTICS OF CO2 IN MICROCHANNEL

Abstract

In this study, we investigated two-phase flow patterns and effects of oil concentration on the heat transfer coefficient and pressure drop of CO 2 undergoing condensation process in a microchannel, and from the data collected, we developed a prediction model of CO 2 condensation heat transfer coefficient in smooth tube and microchannels. The narrow single rectangular channel was utilized to observe flow patterns of CO 2 under the condensation process. Experimental results show that the transition of vapor quality from intermittent flow to annular flow advances with increase of mass flux and with decrease of condensation temperature. The heat transfer coefficient decreased by 50% as compared to that of the pure CO 2 when the oil concentration was increased from 0.7 to 1.2 wt.% for the mass flux of 600 kg ⋅ m-2 ⋅ s-1. The pressure drop slightly decreased with oil concentration as compared to that of pure CO 2. We developed the prediction model for the heat transfer coefficient of CO 2 undergoing condensation process in microchannel by considering the effects of the liquid film thickness and of the interface shape between liquid and vapor phases on the heat transfer coefficient. The present prediction model estimated the experimental data within 18.9% of mean deviation. For the pressure drop in microchannel tubes, the existing models developed by Mishima and Hibiki, and Garimella showed the marginal predictability.