R134a condensation flow regime and pressure drop in horizontal microchannals cooled symmetrically and asymmetrically

An experimental investigation was conducted for two-phase flow regimes and friction pressure drop during condensation of refrigerant R134a in oval parallel microchannels with a hydraulic diameter of 301.6 µm, an aspect ratio of 2.46 and a length of 50 mm. The effects of microchannel cooling methods, including asymmetric cooling and symmetric cooling, were studied. The flow regimes and pressure drops were recorded for qualities of 0.1-0.9 and mass flux of 60-250 kg/(m2 s). The inlet saturation temperature of R134a is 31.3 °C. Film wavy flow, corner wavy flow, slug flow and bubbly flow were observed. The flow regimes were mapped and compared with 8 flow regime maps in the literature. Two flow regime criteria were given using vapor Weber number. The wavy-intermittent flow transition locations were measured and compared with the correlations in the literature. The transition location moves downstream with increasing refrigerant mass flux and inlet quality. The transition locations were more upstream for the condensation flow cooled symmetrically then that cooled asymmetrically. The friction pressure drop increases with increasing mass flux and quality. The pressure drop for microchannels with symmetric cooling is lower than asymmetric cooling. The pressure drop data was compared with the correlations in the literature.