A Multiscale Network Model for Simulating Moisture Transfer Properties of Porous Media

A multiscale network model is presented to model unsaturated moisture transfer in hygroscopic capillary-porous materials showing a broad pore-size distribution. Both capillary effects and water sorption phenomena, water vapour and liquid water transfer are considered. The multiscale approach is based on the concept of examining the porous space at different levels of magnification. The conservation of the water vapour permeability of dry material is used as scaling criterion to link the different pore scales. A macroscopic permeability is deduced from the permeabilities calculated at the different levels of magnification. Each level of magnification is modelled using an isotropic nonplanar 2D cross-squared network. The multiscale network simulates the enhancement of water vapour permeability due to capillary condensation, the hysteresis phenomenon between wetting and drying, and the steep increase of moisture permeability at the critical moisture saturation level. The calculated network permeabilities are compared with experimental data for calcium silicate and ceramic brick and a good agreement is observed.

[1]  Scher,et al.  Simulation and theory of two-phase flow in porous media. , 1992, Physical review. A, Atomic, molecular, and optical physics.

[2]  L. E. Scriven,et al.  Percolation and conduction on Voronoi and triangular networks: a case study in topological disorder , 1984 .

[3]  W. D. Hoff,et al.  Unsaturated water flow within porous materials observed by NMR imaging , 1979, Nature.

[4]  M. Prat.  Isothermal drying on non-hygroscopic capillary-porous materials as an invasion percolation process , 1995 .

[5]  J. Parlange.  Porous Media: Fluid Transport and Pore Structure , 1981 .

[6]  P. Crausse,et al.  Etude fondamentale des transferts couples chaleur-masse en milieu poreux , 1981 .

[7]  W. E. Soll,et al.  A modified percolation approach to simulating three-fluid capillary pressure-saturation relationships , 1993 .

[8]  Ioannis Chatzis,et al.  Network modelling of pore structure and transport properties of porous media , 1993 .

[9]  J. R. Philip,et al.  Moisture movement in porous materials under temperature gradients , 1957 .

[10]  Morrel H. Cohen,et al.  Quantitative methods for microgeometric modeling , 1982 .

[11]  W. Durner.  Hydraulic conductivity estimation for soils with heterogeneous pore structure , 1994 .

[12]  Joel Koplik,et al.  Capillary displacement and percolation in porous media , 1982, Journal of Fluid Mechanics.

[13]  John Crank,et al.  The Mathematics Of Diffusion , 1956 .

[14]  Alkiviades C. Payatakes,et al.  A three dimensional network model for consolidated porous media. Basic studies , 1989 .

[15]  M. Sahimi.  Flow phenomena in rocks : from continuum models to fractals, percolation, cellular automata, and simulated annealing , 1993 .

[16]  F. Dullien,et al.  Simulation of capillary pressure curves using bond correlated site percolation on a simple cubic network , 1987 .

[17]  Cesar Zarcone,et al.  Numerical models and experiments on immiscible displacements in porous media , 1988, Journal of Fluid Mechanics.

[18]  David Wilkinson,et al.  Invasion percolation: a new form of percolation theory , 1983 .

[19]  W. Wise.  A new insight on pore structure and permeability , 1992 .

[20]  Joel Koplik,et al.  Creeping flow in two-dimensional networks , 1982, Journal of Fluid Mechanics.

[21]  J. R. Philip.  Numerical solution of equations of the diffusion type with diffusivity concentration-dependent , 1955 .

[22]  T. J. Lasseter,et al.  Two-phase flow in random network models of porous media , 1985 .

[23]  I. Fatt.  The Network Model of Porous Media , 1956 .

[24]  Ke Xu,et al.  Multiscale Structures to Describe Porous Media Part I: Theoretical Background and Invasion by Fluids , 1997 .

[25]  M. Dias,et al.  Immiscible Microdisplacement and Ganglion Dynamics in Porous Media , 1984 .