Experimental investigation on the boiling heat transfer characteristic of copper surfaces with different hydrophilicity

Abstract

Surface hydrophilicity has a significant effect on boiling heat transfer. In order to systematically investigate the influence of hydrophilic degree on the boiling heat transfer performance, seven different surfaces with gradually changing contact angles (CAs) were prepared using the chemical etching technology. Meanwhile, Visual studies on pool boiling of four of these different hydrophilic surfaces were conducted using a high-speed camera at atmospheric pressure, with deionized water as the working fluid. The influence laws of the hydrophilicity coefficient and relative wall superheat on the enhancement of boiling heat transfer are systematically summarized. It is shown that the boiling heat transfer coefficient (HTC) and critical heat flux (CHF) of the heating surface increased as the CA decreased. Owing to its vertically and horizontally interlaced nanorods and nanoflower structures, the surface oxidized by NaOH/(NH4)2S2O8 has higher surface roughness and larger phase change heat transfer area, resulting in a super-hydrophilic property of the copper surface and a faster bubble detachment frequency. The CHF and boiling HTC were 1.16 and 1.59 times that of the untreated surface, respectively, and the onset of nucleate boiling was advanced by 3.1 K, greatly enhancing boiling heat transfer and exhibiting better heat transfer performance.