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ME-EM Graduate Seminar Speaker Series
Dr. Vahid Vandadi
Abstract: When a colloidal sessile droplet dries on a substrate, the particles suspended in it usually deposit in a ring‐like pattern. This phenomenon is commonly referred to as the “coffee‐ring” effect. One paradigm for why this occurs is as a consequence of the solutes being transported towards the pinned contact line by the flow inside the drop, which is induced by surface evaporation. From this perspective, the role of the liquid‐gas interface in shaping the deposition pattern is somewhat minimized. Here, we propose an alternative mechanism for the coffee‐ring deposition. In our theory the liquid‐gas interface plays a significant role in forming the deposition patterns. We model the interfacial adsorption and transport of particles as a one‐dimensional advection‐generation process in toroidal coordinates and show that the theory not only reproduces ring‐shaped depositions but is also in accord with experimental measurements.
Bio: Dr. Vahid Vandadi is currently a CAE Aero‐Thermal Engineer at Polaris Industries where he works on new techniques to enhance the thermal performance of Continuously Variable Transmission (CVT) systems. Prior to joining Polaris in 2017, he was a Post‐doctoral fellow at the University of Nevada, Reno. He obtained PhD in Mechanical Engineering from University of Nevada, Reno. His research interest includes renewable energy and transport phenomena in micro and macro scale systems.
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