Droplet Evaporation on Hot Micro-Structured Superhydrophobic Surfaces: Analysis of Evaporation from Droplet Cap and Base Surfaces
Droplet Evaporation on Hot Micro-Structured Superhydrophobic Surfaces: Analysis of Evaporation from Droplet Cap and Base Surfaces
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DOI：
10.1016/j.ijheatmasstransfer.2021.122314
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发表时间：
2022-01-13
影响因子：
5.2
通讯作者：
Cheng, Jiangtao
中科院分区：
文献类型：
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作者：
Huang, Wenge;He, Xukun;Cheng, Jiangtao
本研究针对热微结构超疏水表面上固着水滴的蒸发进行实验与理论研究。将4 μ L的水滴放置在微柱硅衬底上，衬底温度加热至120 ℃。建立了一个全面的热路模型，分析了衬底粗糙度和衬底温度对固着液滴蒸发的影响。这是第一次，两个组成部分的热量和质量传递，即，一个来自液滴帽表面，另一个来自液滴底部表面，在液滴蒸发过程中的区别和系统的研究。因此，计算了不同条件下液滴帽表面和液滴底部微柱之间间隙液-气界面的蒸发传热速率。对于在40 ° C - 80 ° C范围内的加热基板上的液滴蒸发，预测的液滴帽温度与实验结果匹配良好。在接触半径恒定的液滴蒸发模式下，液滴底部蒸发速率的降低是导致总蒸发传热速率持续降低的主要原因，而接触角恒定的液滴帽表面蒸发速率的降低是主要原因。考虑内部流体流动对加热到100摄氏度以上的基板上的液滴蒸发的影响，并且采用有效导热率作为校正因子来解释液滴内部对流传热的影响。对于在40摄氏度、60摄氏度、80摄氏度、100摄氏度和120摄氏度下加热的基板上的液滴蒸发，液滴基部和基板基部之间的温度差估计分别为约2摄氏度、5摄氏度、8摄氏度、13摄氏度和18摄氏度，阐明了由于蒸发冷却而引起的加热粗糙表面上的水滴的延迟或抑制沸腾。(c)2021爱思唯尔有限公司保留所有权利。
In this study, evaporation of sessile water droplets on hot micro-structured superhydrophobic surfaces is experimentally and theoretically investigated. Water droplets of 4 mu L are placed on micro-pillared silicon substrates with the substrate temperature heated up to 120 degrees C. A comprehensive thermal circuit model is developed to analyze the effects of substrate roughness and substrate temperature on the sessile droplet evaporation. For the first time, two components of heat and mass transfer, i.e., one from the droplet cap surface and the other from the droplet base surface, during droplet evaporation are distinguished and systematically studied. As such, the evaporation heat transfer rates from both the droplet cap surface and the interstitial liquid-vapor interface between micropillars at the droplet base are calculated in various conditions. For droplet evaporation on the heated substrates in the range of 40 degrees C - 80 degrees C, the predicted droplet cap temperature matches well with the experimental results. During the constant contact radius mode of droplet evaporation, the decrease of evaporation rate from the droplet base contributes most to the continuously decreasing overall evaporation heat transfer rate, whereas the decrease of evaporation rate from the droplet cap surface is dominant in the constant contact angle mode. The influence of internal fluid flow is considered for droplet evaporation on substrates heated above 100 degrees C, and an effective thermal conductivity is adopted as a correction factor to account for the effect of convection heat transfer inside the droplet. Temperature differences between the droplet base and the substrate base are estimated to be about 2 degrees C, 5 degrees C, 8 degrees C, 13 degrees C and 18 degrees C for droplet evaporation on substrates heated at 40 degrees C, 60 degrees C, 80 degrees C, 100 degrees C, and 120 degrees C, respectively, elucidating the delayed or depressed boiling of water droplets on a heated rough surface due to evaporative cooling. (c) 2021 Elsevier Ltd. All rights reserved.