Experimental Study of Structured and Unstructured Roughness Impact on the CHF of Hfe-7100 for Different Saturation Pressures

Abstract

[Abstract] Assessment of pool boiling crisis (Critical Heat Flux - CHF - and its corresponding superheating) is of utmost importance for industrial purposes. This research pays special attention to both the temperature excursion before CHF and its corresponding uncertainty under a wide range of pressures and surface treatments. This experimental approach studies the pool boiling phenomena of saturated Novec HFE-7100 under four different pressures, namely 25, 50, 100, and 200 kPa. Six copper boiling surfaces are reported: four grinded with four different levels of sandpaper and two structured surfaces, crafted by a femtosecond laser. The roughness of the laser surfaces is within that yielded through the grinding procedure, which is interesting for comparison purposes. The yielded results show outstanding evidence: (i) The surface roughness does not modify the CHF for low pressures, which suggests the pertinence to address and determine what a plain surface is for nucleate boiling and (ii) even though both laser treatments enhance the CHF, one of the treatments yielded superheatings for CHF similar to those of the polished test section. It seems that the re-wetting mechanism promoted by the laser treatment is somehow delayed, and thus, enhances the pool boiling feasibility for a wider unexpected range of temperatures.