Study on natural convection characteristics of oil/water emulsions inside a rectangular vessel with vertical heating/cooling walls

Emulsions are mixtures of two immiscible liquids, which are important in various fields such as the food, cosmetics, and pharmaceutical industries. In industrial situations, natural convection may occur inside an emulsion owing to the temperature differences in the emulsion manufacturing and storage processes. Therefore, it is important to understand the natural convection characteristics of an emulsion for effective design of such systems. In the present study, oil-in-water (O/W) emulsions were prepared and the natural convection characteristics of the oil particles of the emulsions inside a rectangular vessel heated from one vertical wall and cooled from the opposite wall were investigated experimentally. Silicone oil was used as the dispersed phase of the O/W emulsion. The test samples were prepared with various oil particle sizes and oil volume fractions. We found that multiple convection layers formed inside the emulsion depending on the wall temperature difference, oil particle size, and oil volume fraction. Furthermore, the Nusselt number of an emulsion with a high oil volume fraction was higher than that of a single-phase fluid.