Marangoni Convection in Evaporating Organic Liquid Droplets on a Nonwetting Substrate.
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.
School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
Aditya
A
Chandramohan
School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
Susmita
S
Dash
School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
Justin A
JA
Weibel
School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
Xuemei
X
Chen
School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
Suresh V
SV
Garimella