Drying of porous materials: Experiments and modelling at pore level

Abstract

Drying of porous materials is important in the processing industry, mainly in food manufacturing. The classical drying theory has been widely studied (Barbosa-Cánovas and Vega-Mercado, 1996). This approach is based on experimental determination of the effective diffusion coefficients as a function of water saturation. A different approach is based on the study of drying mechanisms at pore level (Segura and Toledo, 2005a; Segura and Toledo, 2005b; Laurindo and Prat, 1998). Provided pore geometry, pore topology and wall composition of the porous medium, these coefficients can be predicted. In this work we studied isothermal drying of non-hygroscopic porous media with a mechanism based computer facilitated model of pore-level drying. Simulation results of pore-level drying of non-hygroscopic rigid liquid-wet porous media are presented. Two and three-dimensional pore networks represent pore spaces. Here, I report results of experiments and distributions of liquid and vapor as drying time advances. For the calculation of transport properties, details of pore space and displacement were subsumed in pore conductances (Segura and Toledo, 2005b). Solving for the pressure field in each phase, vapor and liquid, I found a single effective conductance for each phase as a function of liquid saturation. Along with the effective conductance for the liquid-saturated network, the diffusivity of liquid and diffusivity of vapor were calculated.