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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，实验研究了基底电导率对吸湿液体除湿液滴吸收水汽的影响。结果表明，在瞬态传热过程中，基板的导热系数起着至关重要的作用。作为热效应的结果，铜基板上的液滴显示出比低导热率PTFE基板上的液滴略高的蒸汽吸收率。通过对水蒸气压变化的分解分析，发现与温度变化的影响相比，水蒸气吸收过程中溶质浓度的变化对液滴表面水蒸气压的影响更大，从而影响了水蒸气吸收速率。其次，建立了一个润滑型模型，模拟了吸湿离子溶液液滴的蒸发和水蒸气吸收过程。研究结果可以全面阐明液滴运动的控制机制，同时具有正的和负的界面质量通量。阐明了在界面相变过程中，毛细效应、热Marangoni效应和溶质Marangoni效应沿着相互作用，导致了吸湿溶液液滴不同于蒸发挥发液滴的时变行为。这些结论为现有文献中水溶液蒸发液滴周围的树枝状结构和水蒸气吸收过程中的沿着扩展和收缩现象提供了合理的解释。