Analysis of Non-Equilibrium and Equilibrium Models of Heat and Moisture Transfer in a Wet Porous Building Material

Mirosław Seredyński,Michał Kubiś,Tomasz S Wiśniewski,Karol Pietrak,Maciej Jaworski,Piotr Łapka,Michał Wasik,Piotr Furmański,Łukasz Cieślikiewicz

doi:10.3390/en13010214

Abstract

In the proposed paper, non-equilibrium and equilibrium models of heat and moisture transfer through wet building materials are presented and compared. In the former, the mass transfer between liquid and gaseous moisture results from the difference between the partial pressure of water vapor and its saturation value. In the second model, the equilibrium between both phases is assumed. In the non-equilibrium model, liquid moisture can be in the continuous (funicular) or discontinuous (pendular) form. The transfer of moisture for each proposed model is tightly coupled with the energy transfer, which is assumed to be an equilibrium process. The time step and grid size sensitivity analysis of both numerical models are performed primarily. The verification of the model is based also on the numerical data available in literature. Finally, obtained with considered models, temporal variations of moisture content in three locations in the computational domain are compared. Reasonable conformity of results is reported, and discrepancies related to differences in formulations of models are discussed.

Highlights

Transfer of moisture in porous building materials is an important phenomenon related to the drying building structures
Comparison of moisture content shows that the coarsest mesh (i.e., Nx = 30) is not enough for the non-equilibrium model, and a finer mesh should be used
The time step size and mesh density sensitivity analysis reveal that stable and reliable simulations can be performed for moderate time step sizes and mesh densities

Summary

Introduction

Transfer of moisture in porous building materials is an important phenomenon related to the drying building structures. It includes concurrent multi-phase transfer of water in the multi-scale porous structure which is accompanied by heat flow. Several approaches to model combined moisture and heat transfer in various porous materials may be found in literature. Attempts to derive coupled balance equations of moisture and energy were undertaken by Whitaker [1]. Salagniac et al [2] proposed a numerical model of drying a porous material during combined convective, infrared, and microwave heating. The one-dimensional model, based on the approach proposed in [3], consisted of energy, dry air, and total moisture balance equations

Methods

Results

Conclusion