Nucleate Boiling With High Gravity and Large Subcooling

Abstract

Measurements of the heater surface temperature are presented for pool boiling of distilled water in an accelerating system with various subcoolings and levels of heat flux. The ranges of the experimental variables are: heat flux between 0.19 MW/m2 and 1.5 MW/m2, accelerations normal to the flat heating surface from 1 to 100 times earth gravity, and liquid subcoolings between 0 K and 89 K. Increasing sub-cooling first produces an increase and then a decrease in wall superheat, with the eventual cessation of nucleate boiling for certain combinations of conditions. The increase in wall superheat is particularly enhanced at 10g, reaching a maximum value of 9 K at 1.05 MW/m2 with 60 K subcooling. This type of behavior is attributed to the interactions between the fluid temperature distribution in the immediate vicinity of the heater surface as it is influenced by natural convection, the activation of nucleation sites, and the influence of increased buoyancy on the heat transfer associated with each departing bubble.