Drying of Single Particles

The convective heat and mass transfers from a single particle, surrounded by a flowing fluid, have important practical applications in Chemical Engineering. Among them are process component cooling, adsorption, distillation, catalytic reactions, extraction, and drying in fixed and fluidized beds. This chapter is intended to provide a concise vision of the phenomena emerging during the drying of single particles. A case study is presented with the proposition of a mathematical model for the drying process of spherical gel systems considering the effect of fluid flow on mass transfer and shape evolution. The experimental results presented were evaluated under a laminar fluid flow with different particle diameters and fluid velocities. Shrinkage of the samples was observed through digital images, and it was used for the calculations of the shape factors and apparent specific mass. The mathematical model considers two-dimensional mass transfer inside the samples, variable effective diffusivity, linear shrinkage, and non-uniform mass transfer by convection. The results confirmed that the major factor for the mechanical alterations of the spherical gel particles was the non-uniform drying owing to the fact that the mass transfer rates over the forward surface of the sphere are greater than those at the rear hemisphere. The proposed mathematical model represented the two-dimensional moisture profiles inside the sample and their consequent shape evolutions. This chapter attests the need for the consideration of the fluid flow effect on the mathematical modeling and contributes to a better understanding and the technological development of the drying processes.

Keywords: Shrinkage, boundary layer, convection, moisture profiles, mathematical modeling.