Wettability effect on pool boiling heat transfer using a multiscale copper foam surface

To improve thermal performance, the wettability effect on pool boiling heat transfer using copper foam is experimentally studied. A surface oxidation and chemical modification method is employed to modify copper foam surface's wettability. After wettability treatment, the copper foam surface is covered with nanosheet. The average contact angle on 50 PPI super-hydrophobic and super-hydrophilic copper foam surface is 148.7 degrees and nearly 0 degrees, respectively. An experimental platform regarding the thermal performance of subcooled pool boiling heat transfer for deionized water on copper foam with a modified wettability surface is conducted. Results showed that the super-hydrophilic copper foam's surface achieves better boiling heat transfer performance in a medium- or high-heat flux region (q >= 20 W.cm(-2)), while super hydrophobic copper foam surface shows a better performance when q < 20 W.cm(-2). The pool boiling enhancement of wettability-modified surface has been verified compared with flat surface from public work. The maximum heat transfer coefficient in this experiment reaches 19,238 W.m(-2).K-1 for super-hydrophilic surface (50 PPI, 2 mm thickness) at a heat flux of 96 W.cm(-2). The bubble dynamic behavior during pool boiling is observed through a high-speed camera. The visualization showed that the shape, size and number of bubbles on super-hydrophilic copper foam surface during pool boiling are different from that on super-hydrophobic copper foam surface due to different adhesion force and surface tension. As copper foam thickness increases, more bubbles are trapped in the copper foam. By analyzing the heat transfer mechanism in copper foam, it is deduced that the specific copper foam structure conveys a larger heat transfer area, and meanwhile, the micro-nanostructure provides an abundance of nucleation sites. Moreover, a super-hydrophilic surface could promote liquid replenishment for the copper foam. Therefore, wettability-modified copper foam shows great promise in thermal management. (C) 2019 Elsevier Ltd. All rights reserved.