Dependencies for Determining the Thermal Conductivity of Moist Capillary-Porous Materials

Abdrahman Alsabry,Vadzim I Nikitsin,Beata Backiel-Brzozowska

doi:10.3390/en13123211

Abstract

A method of determining the effective thermal conductivity of moist capillary-porous materials has been proposed, in which calculations are carried out while taking into account all components of the system (solid, liquid and gas) at once. The method makes it easy to take into account the way water is distributed in the pore space of the material, either as isolated inclusions (drops) or as a continuous component, depending on the moisture content of the material. In the analysis of heat transport in moist capillary-porous materials, the theory of generalized conductivity is used and the structure of moist material is modeled using an ordered geometric structure consisting of identical unit cells in the form of a cube. An equation is obtained for calculating the effective conductivity of capillary-porous materials with isolated and continuous liquid inclusions, with adiabatic and isothermal division of the unit cell. The proposed method is compared to the previously proposed method of determining the effective thermal conductivity of moist materials, in which the three-component system is gradually reduced to a binary system, showing disadvantages of this method compared to the currently proposed. It has been shown that the proposed formulas grant the possibility of a sufficiently accurate prediction of experimental results using the experimental results of the thermal conductivity of moist aerated concrete.

Highlights

Capillary-porous materials, commonly used in building envelope structures, are exposed to intense thermal and hydric influences during operation
The analysis of works [4,5,6,7] shows that the correct experimental assessment of the thermal conductivity of moist porous materials is very difficult, because the measurements obtained for the same material with the same average moisture content may differ significantly
Two methods of determining the effective thermal conductivity of a moist capillary-porous material considered as a three-component system are compared

Summary

Introduction

Capillary-porous materials, commonly used in building envelope structures, are exposed to intense thermal and hydric influences during operation. The analysis of works [4,5,6,7] shows that the correct experimental assessment of the thermal conductivity of moist porous materials is very difficult, because the measurements obtained for the same material with the same average moisture content may differ significantly (in some cases even several times). This can be explained by the character of wetting the pore surface with liquid (partial or total), the character of moisture distribution in the volume of sample (even or uneven), the measurement method (stationary or non-stationary), etc. The dependencies presented in the current publication are the result of further work in the chosen direction, aimed at simplifying the calculation procedures and extending the possibility of their application to other materials with capillary-porous structure

Problem Description

Dependence

The Method of Consideration of Components

Summary