Combined effects of subcooling and surface orientation on pool boiling of HFE-7100 from a simulated electronic chip

The effects of orientation and subcooling on pool boiling of the HFE-7100 dielectric liquid near atmospheric pressure (0.085 MPa) from a 10 x 10 mm smooth copper surface are investigated experimentally. Results are obtained for inclination angles theta = 0degrees (upward-facing), 30degrees, 60degrees, 90degrees, 120degrees, 150degrees, and 180degrees (downward-facing) and liquid subcoolings DeltaT(sub) = 0, 10, 20, and 30 K. Increasing theta decreases the saturation nucleate boiling heat flux at high surface superheats (DeltaT(sat) > 20 K), but increases it only slightly at lower surface superheats. The critical heat flux (CHF) decreases slowly with increasing theta from 0degrees to 90degrees, and then deceases faster with increasing theta to 180degrees. CHF increases linearly with increased subcooling, but the rate increases from 0.016 K -1 at 0degrees to 0.048 K -1 at 180degrees. At theta = 0degrees and DeltaT(sub) = 30 K, CHF is similar to 36 W/cm(2) and 24.45 W/cm(2) for saturation boiling, while at theta = 180degrees CHF = 10.85 W/cm 2 at DeltaT(sub) = 30 K and only 4.30 W/cm(2) at saturation. The developed correlation for CHF of HFE-7100, as a function of theta and DeltaT(sub) , 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.