Numerical simulation of evaporation and drying of a bi-component droplet

A mathematical model to describe the evaporation and drying behavior of a single quiescent spherical bi-component droplet containing evaporating liquid and dissolved solid substance is developed with primary focus on the application of this model to study the evaporation and drying of a droplet of polymer (Polyvinylpyrrolidone - PVP) in water and Mannitol in water. The water evaporation rate is computed using a convective two-film model with modifications to account for solid layer formation. The non-ideality effect induced by the presence of PVP or Mannitol on vapor pressure of water is accounted through the calculation of activity coefficient of water in either system. The problem under consideration is governed by the continuity (diffusion) and energy equations, which are solved using a finite difference method. The effect of drying conditions such as gas velocity, temperature, and relative humidity on evaporation and drying rate is studied. It is concluded that the present model effectively captures the initial stages of single droplet drying.