COMBINED EFFECTS OF SUBCOOLING AND SURFACE ORIENTATION ON POOL BOILING OF HFE-7100 FROM A SIMULATED ELECTRONIC CHIP

Abstract

The effects of orientation and subcooling on pool boiling of the HFE-7100 dielectric liquid near atmospheric pressure (0.085 MPa) from a 10 × 10 mm smooth copper surface are investigated experimentally. Results are obtained for inclination angles θ = 0° (upward-facing), 30°, 60°, 90°, 120°, 150°, and 180° (downward-facing) and liquid subcoolings ΔTsub = 0, 10, 20, and 30 K. Increasing θ decreases the saturation nucleate boiling heat flux at high surface superheats (ΔTsat > 20 K), but increases it only slightly at lower surface superheats. The critical heat flux (CHF) decreases slowly with increasing θ from 0° to 90°, and then deceases faster with increasing θ to 180°. CHF increases linearly with increased subcooling, but the rate increases from 0.016 K−1 at 0° to 0.048 K−1 at 180°. At θ = 0° and ΔTsub = 30 K, CHF is ∼ 36 W/cm2 and 24.45 W/cm2 for saturation boiling, while at θ = 180° CHF = 10.85 W/cm2 at ΔTsub = 30 K and only 4.30 W/cm2 at saturation. The developed correlation for CHF of HFE-7100, as a function of θ and ΔTsub, is within ±10% of the present data. The recorded still photographs of the boiling surface in the experiments illustrate the effects of liquid subcooling and surface orientation at different nucleate boiling heat fluxes and surface superheats on vapor bubble accumulation and/or induced mixing at the surface.