Critical Heat Flux During Subcooled Flow Boiling in Narrow Rectangular Channels

The critical heat flux during subcooled flow boiling in narrow one-side heated rectangular channels was investigated experimentally using fluorinert liquid PF-5060 as a coolant. Three channel widths were examined, that is 1.3mm, 2.0mm, and 3.0mm. The heating surface was 10mm wide and 200mm long and only vertical upflow was experimented. Experiments were conducted at nearly atmospheric pressure under the following conditions: subcooled coolant mass velocity 2000–5000 kg/m2s; inlet temperature 24–47 °C; exit pressure 1.0–1.4 bar; equilibrium quality at channel exit −0.58 to −0.28. Critical heat flux under the above experimental conditions was found to increase with increase in mass velocity, with decrease in the channel width, and with increase in the inlet subcooling. Visual observations showed that bubbles were small and had diameter less than 100μm. A comparison of the data with correlations reported in the literature showed that the correlations generally tended to overpredict the data. The correlations also do not show a proper trend with respect to the effect of channel width on critical heat flux. A new correlation based on dimensional analysis has been proposed. The correlation proposed can predict experimental data within 20% uncertainty.