An efficient numerical model for the simulation of coupled heat, air, and moisture transfer in porous media

Abstract

This article proposes an efficient explicit numerical model with a relaxed stability condition for the simulation of heat, air, and moisture transfer in porous material. Three innovative approaches are combined to solve the system of two differential advection‐diffusion equations coupled with a purely diffusive equation. First, the DU FORT‐FRANKEL scheme is used to solve the diffusion equation, providing an explicit scheme with an extended stability region. Then, the two advection‐diffusion equations are solved using both the SCHARFETTER‐GUMMEL numerical scheme for the space discretisation and the two‐step RUNGE‐KUTTA method for the time variable. This combination enables to relax the stability condition by one order. The proposed numerical model is evaluated on three case studies. The first one considers quasi‐linear coefficients. The theoretical results of the numerical schemes are confirmed by our computations. Indeed, the stability condition is relaxed by a factor of 40 compared to the standard EULER explicit approach. The second case provides an analytical solution for a weakly nonlinear problem. A very satisfactory accuracy is observed between the reference solution and the one provided by the numerical model. The last case study assumes a more realistic application with nonlinear coefficients and ROBIN‐type boundary conditions. The computational time is reduced 10 times by using the proposed model in comparison with the explicit EULER method.

A critique on “An efficient numerical model for liquid water uptake in porous material and its parameter estimation”

“…Introductorily, this research group has liberally published on the Scharfetter-Gummel method for hygrothermal simulation [1][2][3][4][5], and in all of these publications the efficiency of the scheme is touted. The discusser's Delphin simulations expose the unfounded nature of such claim though, as these are about 50 times faster than [1]'s simulations.…”

“…Tenthly therefore, in this light [1]'s authors are invited to reflect on the merits of their inverse identification in relation to capillary absorption experiments. While they could point out that this application is a mere illustration, one could counter that the principles of Scharfetter-Gummel and inverse identification have been amply illustrated already [2][3][4][5][6][7][8][9]. Conclusively, [1] is a suitable example of the caution to be applied in relation to inverse identification.…”

“…Given that this research group has liberally published on Scharfetter-Gummel for hygrothermal simulation [2][3][4][5] as well as on inverse characterisation for hygrothermal properties [6][7][8][9] already, the single novelty of [1] is its focus on capillary absorption. This critique has voiced serious concerns on the validity of the moisture transfer model defined, of the moisture transfer simulations performed, and of the moisture transfer properties identified, and invites [1]'s authors to counter the formulated concerns, in order to confirm their outcomes' reliability.…”

“…Given that this research group has liberally published on Scharfetter-Gummel for hygrothermal simulation [2][3][4][5] as well as on inverse characterisation for hygrothermal properties [6][7][8][9] already, the single novelty of [1] is its focus on capillary absorption. With respect to that, [1] claims that a simple capillary absorption experiment -wherein only the height of the moisture front is monitored -suffices for a complete characterisation of the moisture storage and transport properties of the material.…”

“…In February 2019 this journal published the article "An efficient numerical model for liquid water uptake in porous material and its parameter estimation" [1], which reintroduces the Scharfetter-Gummel numerical model for simulation of moisture transfer in building materials, and applies it for the inverse characterisation of hygric properties based on a capillary absorption experiment. Given that this research group has liberally published on Scharfetter-Gummel for hygrothermal simulation [2][3][4][5] as well as on inverse characterisation for hygrothermal properties [6][7][8][9] already, the single novelty of [1] is its focus on capillary absorption. This critique however voices serious concerns on the validity of the moisture transfer model defined, of the moisture transfer simulations performed, and of the moisture transfer properties identified.…”