Abstract

Pool boiling experiments are performed to investigate the effects of inclination angle, θ, and average roughness, Ra, of uniformly heated 10 × 10 mm copper surfaces on saturation boiling of HFE-7000 dielectric liquid. Ra varied from 0.039 to 0.1.44 μm and θ from 0° (upward facing) to 180° (downward facing). In addition, high speed images and still photographs of nucleate boiling in the various regions and near CHF are captured to assist the interpretation of experimental results. The values of CHF and the maximum nucleate boiling heat transfer coefficient, hMNB, which occurs near the fully developed nucleate boiling region, increase with increasing Ra and/or decreasing θ. The corresponding surface superheats, however, decrease with increasing θ and/or Ra. In the upward facing orientation, CHF increases from ∼20.7 to ∼30.9 W/cm2 with increasing Ra from 0.039 to 0.144 μm, and the corresponding CHF values in the downward facing orientation are 7.1 and 8.9 W/cm2, respectively. Nucleate boiling heat transfer coefficient, hNB, in the discrete bubbles region at low surface superheats increases, while in the fully developed nucleate boiling region at high superheats it increases with increasing Ra and/or decreasing θ. The developed correlations for CHF and hMNB and corresponding superheats, as functions of Ra and θ, are in good agreement with the experimental data.

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