Experimental investigation of the CHF of HFE-7100 under pool boiling conditions on differently roughened surfaces

Abstract

Nucleate pool boiling experiments with HFE-7100 under saturated conditions are reported. An accurate quasi-steady procedure was introduced to raise boiling curves and attain the Critical Heat Flux condition. The results include boiling curves and Critical Heat Flux data (CHF) for four different surfaces of Brass CuZn39Pb3 at four different pressures, ranging from 25 to 200 kPa. The boiling surfaces were characterized by means of confocal microscopy. Mean roughness of the surface varied from 0.023 μm to 1.878 μm. Contact angles of liquid HFE-7100 with the boiling surfaces were also measured. Critical Heat Flux results were compared with well-known correlations, displaying a general trend agreement with some of them. Critical Heat Flux increases with pressure, and its variation with roughness is more pronounced when pressure is increased. Critical Heat Flux variations with surface topography revealed an increment with roughness up to a certain limit, diminishing for the higher roughness. The dimensionless Critical Heat Flux, designated by K, is solely independent of pressure in the case of the polished surface. This trend suggests the occurrence of a “smooth“ surface characterised by pressure independence Critical Heat Flux.