Heat transfer from a continuous liquid to an evaporating drop : a numerical analysis

Heat transfer from a continuous liquid to a drop of a second immiscible liquid, which rises due to buoyancy and simultaneously evaporates in direct contact to the continuous liquid, is examined numerically. The finite element method in a pure Lagrangian description is applied. The shape of the interfaces has not to be prescribed and the full Navier--Stokes equations are solved. Calculations are performed for a furan drop and for a n-pentane drop evaporating in aqueous glycerol. In the initial stage, when the rising velocity and the vapour fraction of the compound drop are small, heat transfer by conduction dominates. With increasing time convective heat transfer becomes more important, even in the liquid of the dispersed component where a vortex is generated. Most of the heat transfer from the continuous to the dispersed component takes place in a small region at the contact circle of the three phases. Because of convection in the liquid of the compound drop, the heat flux at the internal liquid--vapour interface of the dispersed component and thus the evaporation is distributed more uniformly. Even though the thermal resistance of the drop's liquid is higher than that of the continuous liquid, the share of neither liquid on the total resistance can be neglected