Subcooled boiling critical heat flux of HFE-7000 dielectric liquid on inclined rough Cu

Abstract

This work experimentally investigated the effect of subcooling, ΔTsub, from 0 K (saturation) to 15 K, on nucleate boiling and the Critical Heat Flux (CHF) of HFE-7000 dielectric liquid on uniformly heated 10 × 10 mm inclined rough Cu. The surface average roughness, Ra, increased up to 1.44 μm and the inclination angle, θ, increased from 0o (upward facing) to 180o (downward facing) in 30o increments. The values of the maximum nucleate boiling heat transfer coefficient, hMNB,sub, that occur at end of the fully developed boiling region and those of CHF and of the corresponding surface superheats are correlated to within ±5% of the experimental data as functions of Ra, θ, and ΔTsub. The CHF and hMNB increase with increased Ra and decreased θ to the lowest values in the downward facing orientation. In the upward facing orientation, for 15 K subcooling CHF increases from ~33.6 to ~39 W/cm2 with increased Ra from 0.21 to 1.4 μm. The corresponding CHF values in the downward facing orientation of 11.25 and 14.1 W/cm2, respectively, are 33.5 % and 36.15% of those in the upward facing orientation. CHF increases, while hMNB decreases linearly with increased liquid subcooling. The CHF subcooling coefficient increases, while that of hMNB decreases with increased inclination angle and both are practically independent of Ra. The subcooling coefficients of the surface temperature superheats at both CHF and hMNB, increase with increased liquid subcooling.