Size of departing condensate droplets from radiant cooling ceiling

doi:10.11949/j.issn.0438-1157.20160292

Abstract

Abstract:

The size of condensate droplets departing from horizontal superhydrophobic copper surfaces and conventional aluminum alloy surfaces was studied experimentally and theoretically. During the whole condensation experiment, the dew formation and departure underneath the sample surfaces were imaged by CCD. It was found that the radius of the condensate droplets of the coalescence-induced jumping condensate departed from the superhydrophobic surface was below 300 μm. The coalesced droplets merged by micro-droplets with a radius ratio ranging from 1.0 to 1.5 were subject to self-removal from the superhydrophobic surface. This was because the driving force of the released surface energy after droplet coalescence became dominant compared to the resistance of the work of adhesion and viscous dissipation with the decrease of the radius ratio. In addition, the radii of the gravity-induced falling droplet from conventional aluminum alloy surfaces were ranged from 2.0 mm to 6.0 mm, and limited by the advancing and receding contact angles. Therefore, these results revealed that the superhydrophobic surface can significantly decrease the size of droplets departing from radiant ceiling panels and reduce condensation risks of radiant cooling ceiling systems.

Key words: condensation, superhydrophobic surface, contact angle, thermodynamics, numerical simulation

摘要：

通过对超疏水纯铜样品和4种经过不同表面改性处理的铝合金样品的冷凝实验，系统地研究了表面特性不同的辐射吊顶表面冷凝液滴的脱落尺寸。结果表明，超疏水表面合并诱导脱落的液滴半径不足300 μm，而且尺寸相近的微小液滴（半径之比在1.0～1.5）合并后易于发生液滴脱落。根据能量守恒原理对液滴合并过程进行了理论分析，结果表明随着合并前两液滴半径之比的增大，液滴合并脱落的阻力，黏附功和黏性耗散相比于合并后释放的表面能均变得显著，从而导致液滴合并脱落的概率减小。常规辐射吊顶表面上重力诱导脱落的液滴半径随机分布在2.0～6.0 mm，但在表面的后退角和前进角所确定的上、下限范围内。因此，超疏水处理后的辐射吊顶大幅减小了冷凝液滴的脱落尺寸，可显著降低其表面结露风险。

关键词: 凝结, 超疏水表面, 接触角, 热力学, 数值模拟

CLC Number:

TK124

TANG Haida, ZHANG Tao, LIU Xiaohua, JIANG Yi. Size of departing condensate droplets from radiant cooling ceiling[J]. CIESC Journal, 2016, 67(9): 3552-3558.

唐海达, 张涛, 刘晓华, 江亿. 辐射吊顶表面冷凝液滴脱落尺寸分析[J]. 化工学报, 2016, 67(9): 3552-3558.

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