Influencing factors analysis of condensation heat transfer on hydrophilic-hydrophobic composite surfaces considering droplets dynamic behavior

doi:10.11949/0438-1157.20250010

Abstract

Abstract:

In order to reveal the enhancement effect of the hydrophilic-hydrophobic composite structure surface on condensation heat transfer and the effects of dynamic behavior characteristics of condensate droplets, an experimental system and a mathematical model of condensation on the hydrophilic-hydrophobic composite surface was established. The model is based on the theories of dropwise condensation (DWC) and filmwise condensation (FWC), in combination with the effects of droplets nucleation, merge, detachment, and sliding sweeping. The effects of surface structure size, wettability, operating temperature and droplet dynamic behavior on condensation efficiency were analyzed by the model. The diameter of the circular hydrophobic area on the composite surface is W_DWC, and the interval of the hydrophilic channel is W_FWC. The results show that under different conditions, the condensation coefficient increases first and then decreases with the increase of W_DWC. There is a unique W_DWC corresponding to W_FWC, which makes the condensation coefficient reach the highest. Moreover, the optimal W_DWC is only affected by W_FWC and is insensitive to other factors. The average condensation heat transfer coefficient of the optimal structure size(W_DWC=1.5 mm,W_FWC=0.5 mm) can be increased by 71.4% compared with that of the completely hydrophobic surface at a contact angle of 110°, a steam temperature of 70℃ and a subcooling of 5℃.

Key words: hydrophilic-hydrophobic surface, droplet detachment, merge, sweeping effect, condensation, heat transfer and mass transfer

摘要：

为了揭示亲-疏水复合结构表面对冷凝传热的增强作用和冷凝液滴的动态行为的影响，在滴状冷凝（dropwise condensation，DWC）和膜态冷凝（filmwise condensation，FWC）理论的基础上，结合冷凝液滴成核、合并、脱离和滑动清扫效应，建立了亲-疏水复合表面蒸汽冷凝传热特性试验系统和数学模型，分析了不同表面结构尺寸、蒸汽温度和过冷度下，液滴动态行为对冷凝传热特性的影响。复合表面圆形疏水区直径为W_DWC，亲水通道间隔为W_FWC。结果表明，在不同条件下，冷凝系数随W_DWC的增大先提高后减小，有唯一W_DWC与W_FWC对应，使得冷凝系数达到最高。并且，最佳W_DWC仅受W_FWC的影响明显，对其他因素的影响不敏感。复合表面加速了液滴的脱离，在接触角110°，过冷度为5℃，饱和蒸汽温度为70℃的工况下，最佳结构尺寸（W_DWC=1.5 mm，W_FWC=0.5 mm）相比完全疏水表面冷凝系数提高71.4%。

关键词: 亲-疏水复合表面, 液滴脱离, 合并, 滑动清扫效应, 凝结, 传热传质

CLC Number:

TQ 025.3

Kezheng CHEN, Penghui GAO, Fuchun YAN, Bo CHENG. Influencing factors analysis of condensation heat transfer on hydrophilic-hydrophobic composite surfaces considering droplets dynamic behavior[J]. CIESC Journal, 2025, 76(8): 3976-3989.

陈科拯, 高蓬辉, 焉富春, 程博. 考虑液滴动态行为的亲-疏水复合结构表面冷凝特性影响因素分析[J]. 化工学报, 2025, 76(8): 3976-3989.

Figures/Tables 19

Fig.1 Schematic diagram of hydrophilic-hydrophobic composite surfaces

Fig.2 Preparation process of hydrophilic-hydrophobic composite structure surfaces and surface morphology

Table 1 Surface wetness test results

参数	亲水区	疏水区
左接触角/(°)	65.3	110.4
右接触角/(°)	64.4	109.8
平均接触角/(°)	64.9	110.1
固体黏附功/(mN/m)	119.82	52.97
固体表面能/(mN/m)	69.3	40.6

Fig.3 Experimental system and simulation chamber

Fig.4 Thermocouple layout

Fig.5 Dynamic condensation process of composite surface

Fig.6 Disengagement mode and maximum disengagement radius of droplets

Fig.7 Stationary and moving patterns of droplets

Fig.8 Schematic diagram of droplet merging effect

Fig.9 Droplet sliding and sweeping effect

Fig.10 Schematic diagram of a square computing unit

Fig.11 Variation of sliding speed with height

Fig.12 Variation of droplet coverage and condensation HTC with time

Fig.13 Schematic diagram of enhanced heat transfer of composite structure surface

Fig.14 Influence of composite structure size on condensation heat transfer at θ=100°(Tsat=70℃，ΔT=5℃，θa=110°，θr=95°，δp=2 nm)

Fig.15 Influence of composite structure size on condensation heat transfer at θ=110°(Tsat=70℃，ΔT=5℃，θa=120°，θr=105°，δp=2 nm)

Fig.16 Influence of composite structure size on condensation heat transfer at θ=120°（Tsat=70℃，ΔT=5℃，θa=130°，θr=115°，δp=2 nm）

Fig.17 Influence of Tsat and ΔT on condensation heat transfer

Fig.18 Influence of wettability of composite surface on condensation heat transfer

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