Experimental studies for the combined effects of micro-cavity and surface wettability on saturated pool boiling

Abstract

Experimental studies are conducted to investigate the combined effects of micro-cavities and surface wettability on the pool boiling heat transfer performance and mechanisms. Four types of surfaces are subjected under this study. FS is flat copper surface used as the baseline while MC-FS is flat copper surface modified by micro-cavity structures. MC-SHPi combines micro-cavity structure and superhydrophilicity, and it exhibits excellent boiling heat transfer performance in the high heat flux region. MC-SHPo combines micro-cavity structure and superhydrophobicity, and it yields a better boiling heat transfer performance when the heat flux is lower than 20 W/cm2. The HTCmax is found to be 5.24, 7.21, 9.14 and 12.41 W/cm2·K corresponding to the FS, MC-SHPo, MC-FS, and MC-SHPi following ascending order. MC-FS increases the nucleation sites density due to the existence of irregular multiscale structures of 100 nm – 3 μm on the micro-cavity walls. MC-SHPo further increases the nucleation sites density, as hydrophobicity broadens the size range of effective nucleation site radii. MC-SHPi enhances the bubble departure frequency fd, and the experimental values of fd1/2Db on test surfaces exhibit a linear increase with Jakob number.