Validation of a coupled heat, vapour and liquid moisture transport model for porous materials implemented in CFD

Abstract

Moisture-related damage is an important issue when looking at the performance of building envelopes. In order to accurately predict the moisture behaviour of building components, building designers can resort to Heat, Air and Moisture (HAM) models. In this paper a newly developed heat and mass transfer model that is implemented in a 3D finite volume solver, Fluent®, is presented. This allows a simultaneous modelling approach of both the convective conditions surrounding a porous material and the heat and moisture transport in the porous material governed by diffusion. Unlike most HAM models that often confine to constant convective transport coefficients it is now possible to better predict these convective boundary conditions. An important application of the model is the convective drying of porous building materials. Especially during the first drying stage, the drying rate is determined by the convective boundary conditions. The model was validated against a convective drying experiment from literature, in which a saturated ceramic brick sample is dried by flowing dry air over one side of the sample surface. Temperature and relative humidity measurements at different depths in the sample, moisture distribution profiles and mass loss measurements were compared with simulation results. An overall good agreement between the coupled model and the experiments was found, however, the model predicted the constant drying rate period better than the falling rate period. This was improved by adjusting the material properties. The adjustment of the material properties was supported by neutron radiography measurements.

Drying behaviour of calcium silicate

“…This is in contrast to e.g. the drying experiment with brick [12,[29][30] that was used to validate the coupled heat and mass transfer model and the observation by [10,[32][33][34]. This shows that the use of spatially varying transfer coefficients is not always needed and is very case specific and depends on the material properties, the geometry and 'intensity' of the transfer coefficient distribution.…”

“…In this section only a short description of the model is given. More details on the model can be found in [29,30]. The model has already been validated against a drying experiment from literature [12] in which ceramic brick was used as a hygroscopic and capillary active material.…”

The impact of evaporation from porous tile on roof thermal performance: A case study of Guangzhou’s climatic conditions

“…Moisture migrating through the building envelope may significantly influence indoor air humidity and air-conditioning loads, especially the latent cooling load [32][33][34][35][36]. To reduce the negative influence of moisture migration, we set up a waterproof film between the porous facing tile and cement mortar.…”

More comprehensive 3D modeling of clay‐like material drying

“…In convective drying process there are three drying periods as follow: preheating period, constant drying rate period (CDRP), and falling drying rate period (FDRP) (Figure ). In the preheating period the material with initial temperature starts to be heat up/down to the wet bulb temperature (F‐J or G‐J) and consequently the drying rate will also start to drop/rise (A‐C or B‐C), respectively . The CDRP begins at time in Figure .…”