Dynamics of microscale droplets impinging onto hot surfaces with oxide layers

微尺度液滴撞击具有氧化层的热表面的动力学

基本信息

批准号：
18J11928
负责人：
WANG Zhenying
金额：
$ 1.22万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for JSPS Fellows
财政年份：
2018
资助国家：
日本
起止时间：
2018-04-25 至 2020-03-31
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18J11928/
关键词：
lubrication model vapor absorption droplet liquid desiccant solutal Marangoni capillary flow droplet dynamics wetting and spreading phase change

项目摘要

First,the effect of substrate conductivity on the vapor absorption into hygroscopic liquid desiccant droplets is investigated experimentally. Results indicate that substrate conductivity plays a crucial role in the transient heat transfer process. As a result of the thermal effect, droplets on copper substrates show a slightly higher rate of vapor absorption than those on low-thermal conductivity PTFE substrates. Further analyses by decomposing the variation of water vapor pressure indicate that, compared to the influence of temperature change, the water vapor pressure at the droplet surface is greatly affected by the change of solute concentration during vapor absorption, and therefore the rate of vapor absorption.Second, a lubrication-type model is developed to simulate the evaporation and vapor absorption process of hygroscopic ionic solution droplet. The investigation makes it possible to fully elucidate the governing mechanisms of droplet motions with both positive and negative interfacial mass fluxes. We elucidate that, along with interfacial phase change, the capillary effect, the thermal Marangoni effect and the solutal Marangoni effect interact with each other, and lead to the time-varying behaviors of hygroscopic solution droplets that differ from evaporating volatile droplets. The conclusions provide reasonable explanations for the spreading and contracting phenomena along with vapor absorption, and for the dendritic structures at the periphery of evaporating aqueous solution droplets in the existing literature.

首先，通过实验研究了基材电导率对吸湿性液体干燥剂液滴吸收蒸汽的影响。结果表明，基材电导率在瞬态传热过程中起着至关重要的作用。由于热效应，铜基板上的液滴表现出比低热导率 PTFE 基板上的液滴稍高的蒸汽吸收率。通过分解水蒸气压的变化进一步分析表明，相比于温度变化的影响，液滴表面的水蒸气压受蒸气吸收过程中溶质浓度变化的影响较大，从而影响蒸气吸收的速率。其次，建立了润滑型模型来模拟吸湿性离子溶液液滴的蒸发和蒸汽吸收过程。这项研究使得充分阐明正负界面质量通量下液滴运动的控制机制成为可能。我们阐明，随着界面相变，毛细管效应、热马兰戈尼效应和溶液马兰戈尼效应相互作用，导致吸湿溶液液滴的时变行为与蒸发挥发性液滴不同。这些结论为现有文献中随着蒸气吸收而发生的扩散和收缩现象以及蒸发水溶液液滴外围的树枝状结构提供了合理的解释。