The vaporization characteristics of water-oil emulsion droplets are investigated by highudfidelity computational simulations. One of the key objectives is to identify the physicaludmechanism for the experimentally observed behavior that the component in the dispersedudmicro-droplets always vaporizes first, for both oil-in-water and water-in-oil emulsionuddroplets. The mechanism of this phenomenon has not been clearly understood. In this study,udan Eulerian-Lagrangian method was implemented with a temperature-dependent surfaceudtension model and a dynamic adaptive mesh refinement in order to effectively capture theudthermo-capillary effect of a micro-droplet in an emulsion droplet efficiently. It is found thatudthe temperature difference in an emulsion droplet creates a surface tension gradient alongudthe micro-droplet surface, inducing surface movement. Subsequently, the outer shear flowudand internal flow circulation inside the droplet, referred to as the Marangoni convection, areudcreated. The present study confirms that the Marangoni effect can be sufficiently large touddrive the micro-droplets to the emulsion droplet surface at higher temperature, for bothudwater-in-oil and oil-and-water emulsion droplets. A further parametric study with differentudmicro-droplet sizes and temperature gradients demonstrates that larger micro-dropletsudmove faster with larger temperature gradient. The oil micro-droplet in oil-in-water emulsionuddroplets moves faster due to large temperature gradients by smaller thermal conductivity.
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