Effects of high subcooling on two-phase spray cooling and critical heat flux

Experiments were performed with FC-77 using three full-cone spray nozzles to assess the influence of subcooling on spray performance and critical heat flux (CHF) from a 1.0 × 1.0 cm² test surface. The relatively high boiling point of FC-77 (97 °C at one atmosphere) enabled testing at relatively high levels of subcooling. Increasing the subcooling delayed the onset of boiling but decreased the slope of the nucleate boiling region of the spray boiling curve. The enhancement in CHF was relatively mild at low subcooling and more appreciable at high subcooling. CHF was enhanced by about a 100% when subcooling was increased from 22 to 70 °C, reaching values as high as 349 W/cm². The FC-77 data were combined with prior spray CHF data from several studies into a broad CHF database encompassing different nozzles, fluids, flow rates, spray orientations, and subcoolings. The entire CHF database was used to modify the effect of subcooling in a previous CHF correlation that was developed for relatively low subcoolings. The modified correlation shows excellent predictive capability.