Phase separation enhanced heat transfer via the Ouzo drop

The Greek drink Ouzo, a mixture of water, ethanol, and anise oil, is optically transparent. However, when enough water is added the drink takes on a milky appearance due to the nucleation of oil droplets within the suspension. Recently, an Ouzo drop was observed during evaporation which demonstrated the phase separation at the gas-liquid interface of the droplet as ethanol preferentially evaporates leading to nucleation of microdroplets. As evaporation progresses, the microdroplet formation progresses and the initial droplets are convected into the center of the bulk drop. Importantly this convection results in a strong Marangoni flow that is counter to the typical direction seen in pure fluids. Phase decomposition and separation has been shown to lead to enhanced heat transfer in micro/minichannels but with fluids going through a spinodal decomposition that is temperature induced. Here we demonstrate the change in heat transfer that results from this phase separation for heated droplets. Experiments are conducted for both ethanol-water and ethanol-water-anise oil mixtures undergoing evaporation.