Effect of unidirectional surface roughness on heat transfer performance of spray cooling

In this study, the effects of surface roughness (Ra) on single-phase and two-phase cooling performances of HFE-7100 and water under different coolants, pressures, and subcoolings were studied. The eight surfaces were unidirectionally roughened. A general trend was that the heat transfer increased with increasing Ra. Owing to the larger contact angle and fewer nucleate sites, the smoother surface had poorer heat transfer performance. Visualization was performed to reveal secondary nucleation on the smooth surface. Finally, correlations were developed to predict the heat transfer performance for different values of Ra.