Marangoni Convection in Evaporating Organic Liquid Droplets on a Nonwetting Substrate

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• 作者：Aditya Chandramohan ; Susmita Dash ; Justin A. Weibel ; Xuemei Chen ; Suresh V. Garimella
• 刊名：Langmuir
• 出版年：2016
• 出版时间：May 17, 2016
• 年：2016
• 卷：32
• 期：19
• 页码：4729-4735
• 全文大小：446K
• 年卷期：0
• ISSN：1520-5827

文摘

We quantitatively characterize the flow field inside organic liquid droplets evaporating on a nonwetting substrate. A mushroom-structured surface yields the desired nonwetting behavior with methanol droplets, while use of a cooled substrate (5–15 °C) slows the rate of evaporation to allow quasi-static particle image velocimetry. Visualization reveals a toroidal vortex within the droplet that is characteristic of surface tension-driven flow; we demonstrate by means of a scaling analysis that this recirculating flow is Marangoni convection. The velocities in the droplet are on the order of 10–45 mm/s. Thus, unlike in the case of evaporation on wetting substrates where Marangoni convection can be ignored for the purpose of estimating the evaporation rate, advection due to the surface tension-driven flow plays a dominant role in the heat transfer within an evaporating droplet on a nonwetting substrate because of the large height-to-radius aspect ratio of the droplet. We formulate a reduced-order model that includes advective transport within the droplet for prediction of organic liquid droplet evaporation on a nonwetting substrate and confirm that the predicted temperature differential across the height of the droplet matches experiments.