Local heating effect on thermal Marangoni flow and heat transfer characteristics of an evaporating droplet

This study numerically investigated the thermal Marangoni flow and heat transfer characteristics of an evaporating droplet. Uniform and local heating methods can control the internal flow patterns of a droplet during evaporation. The present study applied the dynamic mesh method to simulate the be-haviors of the liquid-air interface during evaporation. The results revealed that the flow transition inside the droplet appeared in the early stages of evaporation and occurred owing to the temperature varia-tion at the liquid-air interface; these variations eventually yielded surface tension gradients. Moreover, nonuniform evaporation fluxes caused capillary flows that moved from the center of the droplet to the contact line along the substrate. The surface tension gradient along the liquid-air interface had a domi-nant effect on the internal flow, which induced the thermal Marangoni flow. For the local heating cases, different flow patterns appeared, as compared with those that appeared from uniform heating. The flow directions changed according to the local heating conditions owing to the difference in the local surface tensions at the liquid-air interface.(c) 2022 Elsevier Ltd. All rights reserved.