Droplet motion in confined natural convection flows

Abstract

Droplet motion was investigated in a natural convection flow inside a square enclosure using a high order Level Set Method. We analyzed the droplet path for different Rayleigh numbers and several distinct starting points to identify motion patterns. The influence of the droplet’s thermal conductivity and heat capacity on the pathlines was also studied. The model assumes an incompressible flow of two Newtonian fluids with the same viscosity, density, and thermal expansion coefficient. The droplet is clean, with a constant surface tension. The momentum and energy equations are solved assuming the Boussinesq approximation, the continuum model is discretized using finite differences and the pressure-velocity coupling is achieved by the projection method. We have found that the droplet’s behavior is first defined by the flow regime, which can be either linear or non-linear, depending on the Rayleigh number. Also, the droplet can display one of two types of paths: a periodic motion that results in closed paths or a helical motion starting from its initial position towards the center of the enclosure. The droplet releasing position can have a large effect on the final path. Furthermore, the motion patterns are also affected by the thermal properties of the droplet.