Study on evaporation characteristics of sessile droplet on a convex substrate at constant temperature

doi:10.11949/0438-1157.20221227

Abstract

Abstract:

In this paper, experimental and theoretical studies on the evaporation process of sessile droplets on a convex constant temperature substrate were carried out. In the aspect of experimental research, a visual experimental system for evaporation of distilled water droplets on a convex constant temperature substrate was developed to capture the morphological changes during droplet evaporation process, and the temperature distribution on the droplet surface was obtained by using an infrared thermal imager. In terms of theoretical research, a heat and mass transfer model for the sessile droplet evaporation on a convex constant temperature substrate was established based on an annular coordinate system, and analytical solutions of the temperature distribution inside the droplets and the concentration distribution of the surrounding vapor were derived. The model results are compared with the experimental data to verify the reliability of the calculation model. The results show that the evaporative cooling effect should be considered in the model calculation. Increasing the substrate temperature and decreasing the substrate curvature diameter can increase droplet evaporation rate. Compared with the plane substrate, the spreading radius of the droplets on the convex substrate is larger, the pinning time is longer, and the total evaporation time is reduced. The droplet evaporation mainly follows the constant contact radius evaporation mode. In addition, the excess temperature at the droplet/air interface increases monotonously along the direction from the center of the droplet surface to the contact line, and the overall temperature distribution of the droplet tends to be uniform as the evaporation process proceeds. The results help to understand the heat and mass transfer mechanism of sessile droplet evaporation on a convex substrate.

Key words: droplet evaporation, convex substrate, heat and mass transfer, temperature distribution

摘要：

针对凸面恒温基底上的固着液滴蒸发过程开展了实验和理论研究。实验研究方面，搭建了凸面恒温基底上蒸馏水液滴蒸发的可视化实验系统，捕获了液滴蒸发过程形态变化，使用红外热像仪获得了液滴表面温度分布。理论研究方面，基于环形坐标系建立了凸面恒温基底上固着液滴蒸发的传热传质模型，推导出液滴内部温度分布及其周围蒸气浓度分布的解析解。将模型结果与实验数据进行对比，验证了计算模型的可靠性。研究结果表明：模型计算需考虑蒸发冷却效应，提高基底温度和减小基底曲率直径均可提高液滴蒸发速率；相较于平面基底，凸面基底上液滴的铺展半径更大，钉扎时间延长，总蒸发时间减小，液滴蒸发主要遵循恒定接触半径蒸发模式。此外，液滴/空气界面处的过余温度沿液滴表面从中心到接触线方向单调递增，随着蒸发过程的进行，液滴整体温度分布趋于均匀。研究结果有助于深入掌握凸面基底上固着液滴蒸发的传热传质机理。

关键词: 液滴蒸发, 凸面基底, 传热传质, 温度分布

CLC Number:

O 359⁺.1

Shulei ZHANG, Bingjie LI, Jian JIANG, Xinyu DONG, Lu LIU. Study on evaporation characteristics of sessile droplet on a convex substrate at constant temperature[J]. CIESC Journal, 2022, 73(12): 5537-5546.

张舒蕾, 李冰杰, 蒋健, 董新宇, 刘璐. 凸面恒温基底上固着液滴蒸发特性研究[J]. 化工学报, 2022, 73(12): 5537-5546.

Figures/Tables 10

Fig.1 Experimental setup of sessile droplet evaporation on a convex substrate at constant temperature

Fig.2 Schematic diagram of physical model[27]

Fig.3 Morphological evolution of sessile water droplet evaporation on convex substrate(V0 = 5 µl，Tw = 72.6℃，D0 = 40 mm)

Fig.4 Variation of contact radius with time during sessile water droplet evaporation with different initial volumes on convex substrate(Tw = 72.6℃，D0 = 40 mm)

Fig.5 Morphological evolution of evaporation process of sessile water droplet on flat substrate(V0 = 5 µl，Tw = 72.6℃)

Fig.6 Variation of contact radius with time during water droplet evaporation on different substrate surfaces(V0 = 5 µl，Tw = 72.6℃)

Fig.7 Infrared thermography of evaporation process of water droplets on convex substrate(V0 = 5 µl，Tw = 72.6℃，D0 = 40 mm)

Fig.8 Comparison between calculated results and experimental data

Fig.9 Temperature distribution of droplet evaporation calculated by the model(V0 = 5 µl，Tw = 72.6℃，D0 = 40 mm)

Fig.10 Comparison between calculated and experimental values of excess temperature of liquid droplet gas-liquid interface on substrates with different curvature diameters(V0 = 5 µl，Tw = 72.6℃)

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