The Influence of Surface Roughness on Nucleate Pool Boiling Heat Transfer

The effect of surface roughness on pool boiling heat transfer is experimentally explored over a wide range of roughness values in water and Fluorinert^™ FC-77, two fluids with different thermal properties and wetting characteristics. The test surfaces ranged from a polished surface (⁠$Ra$ between $0.027μm$ and $0.038μm$⁠) to electrical discharge machined (EDM) surfaces with a roughness $(Ra)$ ranging from $1.08μm$ to $10.0μm$⁠. Different trends were observed in the heat transfer coefficient with respect to the surface roughness between the two fluids on the same set of surfaces. For FC-77, the heat transfer coefficient was found to continually increase with increasing roughness. For water, on the other hand, EDM surfaces of intermediate roughness displayed similar heat transfer coefficients that were higher than for the polished surface, while the roughest surface showed the highest heat transfer coefficients. The heat transfer coefficients were more strongly influenced by surface roughness with FC-77 than with water. For FC-77, the roughest surface produced 210% higher heat transfer coefficients than the polished surface while for water, a more modest 100% enhancement was measured between the same set of surfaces. Although the results highlight the inadequacy of characterizing nucleate pool boiling data using $Ra$⁠, the observed effect of roughness was correlated using $h∝Ram$ as has been done in several prior studies. The experimental results were compared with predictions from several widely used correlations in the literature.