单面加热微细窄通道内过冷沸腾的传热特性

n experimental study of subcooled flow boiling in a high-aspect-ratio, one-sided heating rectangular channel with a gap of 0.52 mm was conducted using deionized water. The heated length was 30 mm and hence the heated length-to-diameter ratio was about 31.9. The local heat transfer coefficient, pressure drop, and flow pattern of subcooled boiling were measured. The influence of heat flux, mass flux and channel orientation were studied with the aid of a high-speed camera. The results show that the flow pattern of vertical upflow boiling is time-dependent and governed by isolated bubbly flow. It was observed that elongated bubble can be formed frequently at higher heat fluxes either by one nucleated bubble or by bubbles combination. At relatively high mass fluxes (300, 400 kg/m2s), the elongated bubble was pushed out of the heated section immediately owing to larger inertia force. At the lowest mass flux (200 kg/m2s), the elongated bubble tended to expand upstream and finally covered the whole heated section, leading to thin-film evaporation beneath the elongated bubble and hence the enhancement of heat transfer coefficient. The evaporation process is accompanied by partial dryout and rewetting. Finally, temperature and pressure drop oscillations with higher amplitude were observed for the horizontally positioned channel. The merged bubbles agglomerate in the heated section for the horizontal orientation under conditions of low heat fluxes, resulting in earlier partial dryout which deteriorates the heat transfe.