Modeling and Simulation of the Evaporation and Drying of A Two Component Slurry Droplet

Abstract

In this paper, we present a mathematical model and numerical simulation of the evaporation and drying process of a liquid droplet containing suspended solids. This type of drying is commonly encountered in manufacturing processes such as spray drying and spray pyrolysis, which have applications in industries such as food and pharmaceuticals. The proposed model consists of three stages. In the first stage, we consider the evaporation of the liquid in the presence of solid particles. The second stage involves the formation of a porous crust around a wet core region, with liquid evaporation occurring through the crust layer. Finally, the third stage involves sensible heating of the dry particle to reach ambient temperature. To solve the physical models governing these processes, we use a finite difference method with a moving grid methodology. This allows us to account for the moving interface between the crust and the wet core region of the droplet. In this study, we use a non-uniform temperature model that takes into account the spatial variation of temperature inside the droplet. We also assess the validity of a uniform temperature model. To validate our model, we compare it with experimental data on the drying of a single droplet containing colloidal silica particles. We find that our model agrees well with the experimental results. We rigorously examine assumptions made in the model, such as the shape of the solid particles and the continuum flow of vapor through the porous crust. In addition, we analyze the effects of drying conditions, such as the velocity, temperature, relative humidity, and concentration of solid particles, on the drying rate and the final morphology of the particle. Finally, we develop a regime map that can be used to determine whether the final particle will be solid or hollow, based on the operating conditions.

Keywords: Droplet evaporation, Spray Drying, Slurry droplet, Porous media flow