Anisotropic Heat Transfer Induced by Microscale Hydrodynamics of a Single Droplet under Shear

The heat transfer characteristics of a single droplet in a simple shear flow have been numerically studied over a wide range of parameters. The heat transfer in the vertical and lateral directions, and heat exchange between the carrier flow and the droplet have been considered. In the presence of surface tension, the interaction between the carrier flow and the droplet generates a microscale recirculating flow inside the droplet, which drives the surrounding fluid to recirculate through viscous effect. The recirculating flows demonstrate obvious three-dimensional features, and causes anisotropic heat transfer enhancement through advection. The enhancement is stronger at larger Peclet numbers. The droplet behaviors are governed by two nondimensional parameters, the capillary number and viscosity ratio. Below a critical capillary number, which depends on viscosity ratio, the droplet extends in the streamwise direction at a certain inclination angle. Above the critical capillary number, the droplet breaks up into several smaller droplets. When viscosity ratio is greater than a critical value, the droplet tumbles until an elliptical shape is obtained. The droplet motility and deformation make the heat transfer characteristics more complicated. The effect of each of the known parameters (including Reynolds, capillary, and Prandtl numbers) on the heat transfer processes has been examined. This research offers promising potential for the accurate control of the heat and mass transfer in emulsions.