Pool boiling heat transfer on heterogeneous wetting microchannel surfaces

doi:10.11949/j.issn.0438-1157.20161587

Abstract

Abstract:

Three types of microchannel surface (TS#1, TS#2, and TS#3) with non-uniform wettability were fabricated on bare copper surfaces by surface modification technology and electrical discharge machining (EDM). Each microchannel had the same rectangular cross section with a depth of 800 μm and width of 600 μm. The width of fin between two successive microchannels was also 600 μm. All these three microchannel surfaces had the same contact angle of 113.2° for the sidewall and bottom surfaces, but for the top surfaces, the contact angles were 8.6°(TS#1), 88.1°(TS#2) and 156.1°(TS#3), respectively. During the EDM fabrication process, cavities of 10 μm in size was formed due to the electric sparking. Thus, the fabricated microchannel surfaces were multiscale surfaces. The statured pool boiling heat transfer characteristics of deionized water on these three types of microchannel surface as well as the bare copper surface were investigated experimentally. Compared with the bare copper surface (BS, θ=88.6°), all these three microchannel surface with non-uniform wettability manifested a better heat transfer performance. The critical heat fluxes for TS#1 and TS#3 were increased by 61% and 35% compared with BS, while the maximum heat transfer coefficients were increased by 2.3 and 6 times. The bubble dynamics on the heated microchannel surfaces was visualized with a high speed camera. It was found that the surface property of non-uniform wettability can postpone bubble column coalescence, thus the gaps among bubble columns can provide the effective routes for the liquid supplementary to the heated surface, avoiding the occurrence of dry-out and enhancing the critical heat flux.

Key words: heterogeneous wettability, microchannels, heat transfer, bubble, critical heat flux

摘要：

采用高温热氧化与表面改性技术并结合电火花线切割工艺在紫铜表面制备了3类非均匀润湿性微通道表面，微通道顶部接触角分别为8.6°、88.1°、156.1°，通道内部接触角为113.2°。经饱和池沸腾试验表明，具有超亲水性顶部（θ=8.6°）和超疏水顶部（θ=156.1°）的微通道表面临界热通量分别较紫铜表面（θ=88.1°）提高了61%和35%，最大传热系数分别提高了2.3倍和6倍。气泡动力学可视化研究表明：非均匀润湿结构能够显著抑制气泡的合并与团聚，使得气泡之间存在的间隙成为液体补充路径，这是临界热通量提高的主要机理。

关键词: 非均匀润湿性, 微通道, 传热, 气泡, 临界热通量

CLC Number:

TK124

CHAI Yongzhi, ZHANG Wei, LI Ya, ZHAO Yadong. Pool boiling heat transfer on heterogeneous wetting microchannel surfaces[J]. CIESC Journal, 2017, 68(5): 1852-1859.

柴永志, 张伟, 李亚, 赵亚东. 非均匀润湿性微通道表面池沸腾换热特性[J]. 化工学报, 2017, 68(5): 1852-1859.

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