Experimental investigations of condensation droplet shedding characteristics on star-shaped hydrophobic-hydrophilic hybrid surfaces

doi:10.11949/0438-1157.20250070

Abstract

Abstract:

Steam condensation exhibits high heat transfer efficiency and is playing a crucial role in applications such as power and electric generation, aerospace engineering, nuclear engineering, air-conditioning, etc. This paper reports experimental investigations of condensation droplet shedding performances on star-shaped hydrophobic-hydrophilic hybrid surfaces. Testing surfaces are designed and fabricated first, then the experimental system and procedures are introduced. Visualization studies are carried out on the droplet shedding characteristics of three types of hybrid surface, i.e. four-star, five-star and six-star hydrophilic region designs. The droplet shedding diameter, initial droplet shedding time and droplet shedding frequency of the combined surface and the pure hydrophobic surface were compared and analyzed, and the residual condensate area and its distribution characteristics of the droplet shedding hydrophilic region of the combined surface were calculated and statistically analyzed. The results reveal that hybrid surfaces enable high-frequency droplet shedding with large droplet size compared with hydrophobic surfaces, which means higher condensate refreshing rate and enhanced condensation heat transfer performance.

Key words: condensation, two-phase flow, heat transfer, hydrophobic-hydrophilic hybrid surfaces, droplet dynamics, experimental investigations

摘要：

蒸汽冷凝以其高效换热效率，在动力发电、航空航天、核工业、空调制冷等领域发挥着重要作用。本研究设计制备星形亲水区组合表面，结合可视化研究阐释了四角、五角、六角星组合表面液滴脱落形态，对比分析了组合表面与纯疏水表面液滴脱落直径、液滴初始脱落时间、液滴脱落频率差异，计算统计了组合表面液滴脱落亲水区剩余凝液面积及其分布特性。结果表明，组合表面促进液滴以较大尺寸快速脱落，加速凝液排出，强化冷凝换热。

关键词: 凝结, 两相流, 换热, 亲疏水组合表面, 液滴动力学, 实验研究

CLC Number:

TK 124

Lu LIU, Ying YANG, Haowen YANG, Tai WANG, Teng WANG, Xinyu DONG, Run YAN. Experimental investigations of condensation droplet shedding characteristics on star-shaped hydrophobic-hydrophilic hybrid surfaces[J]. CIESC Journal, 2025, 76(8): 3905-3914.

刘璐, 杨莹, 杨浩文, 王太, 王腾, 董新宇, 闫润. 星形亲水区组合表面冷凝液滴脱落特性实验研究[J]. 化工学报, 2025, 76(8): 3905-3914.

Figures/Tables 12

Fig.1 Hydrophobic-hydrophilic hybrid surface preparation process

Table 1 Hydrophilic， hydrophobic， hydrophobic-hydrophilic hybrid testing surfaces parameters

图案类型	内切圆半径/mm	外切圆半径/mm	亲水区总面积占比/%
亲水表面	—	—	100
疏水表面	—	—	0
四角星组合表面	1.13	3.20	20
五角星组合表面	1.18	3.09	20
六角星组合表面	1.20	3.00	20

Fig.2 Scanning electron microscope (SEM) of hydrophobic-hydrophilic hybrid surfaces hydrophobic regions (a), hydrophilic regions (b) and relevant contact angle measurements

Fig.3 Condensation droplet dynamics visualization system

Fig.4 Visualization of droplet merging from hydrophobic to hydrophilic regions on four-point (a), five-point (b), six-point star (c) hybrid surfaces（red dotted regions）

Fig.5 Droplet shedding of four-point (a), five-point (b), six-point star (c) hybrid surfaces

Fig.6 Four-point star ellipse vertical (a) and tilted (b), five-point star ellipse vertical (c) and tilted (d), six-point star ellipse vertical (e) and tilted (f) conditions with real test figure marks

Fig.7 Condensation droplet maximum (a) and minimum (b) Feret diameter and detailed comparison of three hybrid surfaces(c)

Fig.8 Droplet initial shedding moment (a) and continuous shedding frequency (b)

Fig.9 Collected condensate of different condensing surfaces under 10 min steam condensation

Fig.10 Post droplet-shedding residual condensate area measurement on four-star (a), five-star (b) and six-star (c) hydrophilic regions

Fig.11 Area distribution diagram of post-droplet-shedding residual condensate area on four-star (a), five-star (b) and six-star (c) hydrophilic regions

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