Influence of Pore Size Distribution on Drying Kinetics: A Simple Capillary Model

Abstract

In this article, convection drying of a porous medium is described by a capillary model. The simplest form of this model was introduced by Krischer for two parallel capillaries to describe fundamental phenomena of drying kinetics such as the existence of a constant rate period and a falling rate period. The model accounts for capillary pressure, mass transfer is described by liquid water convection and vapor diffusion in the capillaries and at the surface, and isothermal conditions are assumed. This theoretical model is extended to a larger (arbitrary) number of capillaries with a size distribution in order to better represent the situation in a real porous medium. Drying curves as well as moisture profiles in the solid are presented for different pore size distributions. In a second step, the isothermal condition is abandoned and heat transfer into the porous medium is included into the theoretical description for the case of two capillaries. Drying curves and the time-dependent temperature profile in the solid are shown.

Keywords:

• Capillary porous media
• Drying curves
• Moisture profiles
• Temperature profiles

ACKNOWLEDGEMENTS

The authors would like to thank the Graduiertenkolleg 828 Micro-Macro-Interactions in Structured Media and Particle Systems (funded by the German Research Foundation) for its financial support.