Suscripción a Biblioteca: Guest
Portal Digitalde Biblioteca Digital eLibros Revistas Referencias y Libros de Ponencias Colecciones
Journal of Porous Media
Factor de Impacto: 1.49 Factor de Impacto de 5 años: 1.159 SJR: 0.43 SNIP: 0.671 CiteScore™: 1.58

ISSN Imprimir: 1091-028X
ISSN En Línea: 1934-0508

Volumen 23, 2020 Volumen 22, 2019 Volumen 21, 2018 Volumen 20, 2017 Volumen 19, 2016 Volumen 18, 2015 Volumen 17, 2014 Volumen 16, 2013 Volumen 15, 2012 Volumen 14, 2011 Volumen 13, 2010 Volumen 12, 2009 Volumen 11, 2008 Volumen 10, 2007 Volumen 9, 2006 Volumen 8, 2005 Volumen 7, 2004 Volumen 6, 2003 Volumen 5, 2002 Volumen 4, 2001 Volumen 3, 2000 Volumen 2, 1999 Volumen 1, 1998

Journal of Porous Media

DOI: 10.1615/JPorMedia.v13.i1.10
pages 1-11


Yoshito Nakashima
National Institute of Advanced Industrial Science and Technology (AIST), Central 7, Higashi 1-1-1, Tsukuba, Ibaraki 305-8567, Japan
Susumu Kamiya
National Institute of Advanced Industrial Science and Technology (AIST), Central 7, Higashi 1-1-1, Tsukuba, Ibaraki 305-8567, Japan


Some porous media possess fibrous structures. Examples include the geologically deformed porous rocks, white matter in human brain tissue, and fiber-reinforced composite materials. These anisotropic porous media show strong diffusive anisotropy. This study focused on a system consisting of randomly placed parallel rods as a model of fibrous porous media, and describes the analysis of three-dimensional diffusive anisotropy through the lattice random walk computer simulations. The rods were completely impermeable, and nonsorbing random walkers migrate in the percolated pore space between the parallel rods. Direction-dependent self-diffusivity was calculated by taking the time derivative of the mean square displacement of the walkers, and its three-dimensional shape was expressed graphically as a shell-like object by polar representation. Systematic simulations for varied rod packing densities revealed that the shell-like object was no longer convex ellipsoidal, but was constricted in the direction normal to the rod axis when the maximum-to-minimum diffusivity ratio of the diffusion ellipsoids exceeded 1.5 (i.e., when the rod volume fraction exceeded 34 vol %). An analytical solution of the direction-dependent self-diffusivity with constriction is presented for the lattice walk along a straight pore. The solution suggests that the ellipsoid constriction observed for the randomly placed parallel rods is a remnant of the anisotropic pore structure of the hexagonal closest packing, which is the end member of the rod packing. The onset condition of the constriction of the shape of the direction-dependent self-diffusivity is investigated analytically using a diffusion tensor expression. The analysis reveals that the constriction occurs when the maximum-to-minimum diffusivity ratio exceeds exactly 1.5, which agrees well with the simulation results. The critical value of 1.5 can also be applicable to the geologically deformed natural porous rocks having more complex pore structure compared with the simple rod packing system.