Estimation of the drying process in porous media using the parallel and series moisture transfer model

Abstract

Moisture transfer is a very common phenomenon in a wide range of engineering fields, such as civil engineering (cement-based constructions), food processing, mining and soil penetration, drying and imbibition of porous media (including phase change materials), etc. Based on the diffusion assumptions, the classical adopted model (especially for drying) is completed by the liquid permeation. However, it is still inadequate to compromise the complexity of the porous structures. In this work, we propose a “parallel -series assumption” of moisture transferring pattern, comprising different forms of moisture presence and the coupling styles, achieved by an interpolation factor to cover all the possible contribution ratios of the two patterns. Experimentally, we perform the drying of low porosity material under two ambient conditions over 160 days on both local and global parameters, ie., relative humidity (RH) and mass loss (ML). In the simulation part, a nonlinear diffusion-drying model containing liquid permeation and vapor diffusion in the transfer mechanism is applied to estimate the drying process, and compared with the experiment data. Results show different tendency for the two cases of either the permeation dominating case or the no-dominating case. This approach also clarifies the transition from evaporation of weak permeability for vapor diffusivity (square root behavior) towards the linear and faster behavior, which is observed in more porous and permeable materials for the vapor diffusion.