New approaches to hydrodynamic modelling of heating and evaporation of droplets and liquid films

Some of the most recent developments in the modelling of droplet and liquid film heating and evaporation, published in the International Journal of Heat and Mass Transfer in 2018-2019, are reviewed. These developments are focused
on droplet drying with a pharmaceutical application, liquid film heating and evaporation with automotive applications, and micro-explosions in water-fuel emulsion droplets with automotive applications. The new model for drying of
spherical droplets is based on the analytical solutions to the species diffusion and heat transfer equations inside droplets. Solid particles, or a non-evaporating substance dissolved in the liquid, are treated as a non-evaporating component. The model was used to analyse the spray of chitosan dissolved in water. The predicted size of the residual solid balls was shown to be consistent with that observed experimentally. The new model for multicomponent liquid film heating and evaporation is based on the analytical solutions to the species diffusion and heat transfer equations inside the film. The Robin boundary condition at the film surface, and the Dirichlet boundary condition at the wall, were used for the solution to the heat transfer equation. The Neumann boundary conditions at
the wall, and Robin boundary conditions at the film surface, were used to solve the species diffusion equation. The constant convective heat transfer coefficient was assumed. The convective mass transfer coefficient was estimated from the Chilton-Colburn analogy. The model was applied to the analysis of a film composed of a 50%/50% mixture of heptane/hexadecane in Diesel engine conditions. The new model for the puffing/micro-explosion of water-fuel
emulsion droplets is based on the assumption that a small spherical water sub-droplet is located in the centre of a fuel (n-dodecane) droplet. The heat conduction equation is solved inside this droplet using the Dirichlet boundary
condition at its surface. It is assumed that the puffing/micro-explosion process starts when the temperature between water and fuel reaches the boiling temperature of water. The model predictions are shown to be consistent with
available experimental data referring to the time to puffing/micro-explosion.