Effect of liquid static pressure on critical heat flux characteristics in low-pressure pool boiling for dielectric fluid Novec 7100

Abstract

Two-phase direct immersion cooling with dielectric fluid offers excellent heat dissipation, as the demand for high-performance cooling increases due to the high performance and compactness of electronic devices. In this study, the effect of liquid static pressure on the heat transfer characteristics of pool boiling is investigated experimentally for the dielectric fluid Novec7100 under low-pressure conditions on a horizontal heating surface with liquid heights (H) ranging from 3 to 57 mm. The measurements reveal that the self-induced subcooled boiling effect on the critical heat flux (CHF) strongly depends on H and system saturation pressure. A unique subcooled boiling behavior, characterized by disappearing rising bubbles, is observed in the low-pressure range. The CHF initially decreases with lowering system pressure in lower pressure range. However, with further decreases in pressure, approaching liquid static pressure, CHF increase intensifies due to self-induced subcooled boiling, and the effect of H becomes more pronounced. In such low-pressure boiling, even if the overall system is near temperature equilibrium, it is necessary to consider the effect of subcooling near the heating surface. In correlations for saturated boiling, lower pressure results in greater discrepancies with measurements. However, the modified subcooled boiling correlation yields better qualitative and quantitative agreement.