Effect of heterogeneous wetting surface characteristics on flow boiling performance

• Published in: The International journal of heat and fluid flow Vol. 70; pp. 141 - 151
• Main Authors: Kim, Jin Man, Kim, TaeJoo, Yu, Dong In, Noh, Hyunwoo, Kim, Moo Hwan, Moriyama, Kiyofumi, Park, Hyun Sun
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.04.2018
• Subjects: Boiling heat transfer; Critical heat flux; Flow boiling; Hydrophobic stripe; Flow boiling; Hydrophobic stripe; Boiling heat transfer; Critical heat flux
• ISSN: 0142-727X; 1879-2278
• DOI: 10.1016/j.ijheatfluidflow.2018.02.006

•Parallel or crossed hydrophobic stripes were designed with widths of 3 or 1 mm.•The parallel striped surfaces showed higher CHFs than the crossed surfaces.•The crossed striped surface having a width of 1 mm showed the highest BHT.•The boiling characteristics were explained by the merging and breakup of bubbles. A hydrophobic surface promotes bubble nucleation due to hydrophobicity. Thus, a hydrophobic surface has a higher boiling heat transfer coefficient (BHTC) than a hydrophilic surface. In contrast, a hydrophilic surface supplies liquid to a heating surface. This mechanism enhances the critical heat flux (CHF). In this respect, there is a trade-off between a hydrophobic and a hydrophilic surface. In this study, we examined the effect of heterogeneous wetting surfaces on flow boiling performance. We designed four types of hydrophobic stripes; there are two directions, parallel and crossed to the flow, and the width (the pitch) of the hydrophobic stripes in each direction is 3 or 1 mm. In the macro-channel, the flow boiling performance on the surfaces depended on the patterns. The parallel striped surfaces had higher CHFs than the crossed striped surfaces. In addition, the narrow patterns in each direction had higher CHFs than the wide patterns. The difference in BHTC among the parallel striped surfaces was not large, but the difference in BHTC among the crossed striped surfaces was considerable. A visualization technique revealed that the merging and confinement of bubbles were key factors in explaining the boiling characteristics. Considering the drag coefficient and bubble breakup, we suggest appropriate designs of the hydrophobic pattern for the improvement of BHTC and CHF in the flow boiling performance.