Viscous Permeability of Random Fiber Structures: Comparison of Electrical and Diffusional Estimates with Experimental and Analytical Results

Abstract

An investigation of the permeability for viscous flow through random fiber structures used as preforms in composite fabrication processes is presented. A method derived from the electrical conduction principles is employed to predict the viscous permeability of the fiber structures directly from their formation factor, specific surface area, and porosity. The recent Brownian diffusion random-walk simulation results on the molecular survival time are used to derive an upper bound and an approximation to the viscous permeability of these structures. The results are compared to experimental data and theoretical models of the literature. It is found that the conduction-based method provides very good permeability estimates in most cases, resulting in an overall ratio of the theoretical prediction to experimental measurement in the proximity of 1 for the over 500 experimental points utilized. This is one of the most comprehensive experimental validations of the conduction-based method to date and its first validation for anisotropic particle beds. A tortuosity analysis indicates a stronger pore-geometry effect on viscous flow relative to any type of diffusional flow, enhancing the understanding of the differences between pressure-driven and diffusion-driven composite manufacturing techniques.

3D analysis, modeling and simulation of transport processes in compressed fibrous microstructures, using the Lattice Boltzmann method

“…But for real structures they observed dependencies of the calculated permeabilites from the resolution of the images representing their geometry and from the resolution of their lattice. For complex geometries it is known that the Kozeny constant is related to the tortuosity τ [59]. This leads to…”

“…The tortuosity of random overlapping fiber structures was calculated analytically by Tomadakis and Robertson [59]. Their approach of 2-dimensiomal overlapping fiber structures is equivalent to the Thiedmann model of the fiber based geometry without binder.…”

Three-dimensional reconstruction of a random fibrous medium: Geometry, transport, and sound absorbing properties

“…It would be particularly valuable to have a manageable set of geometrical parameters of the three-dimensional (3D) fiber web morphology, in terms of which the transport (e.g., static viscous k 0 and thermal k 0 0 permeabilities, viscous characteristic length K, high frequency tortuosity a 1 ) and acoustical properties of non-woven fibrous media could be described. Obvious candidates for these parameters are the fiber diameters and the angular orientation distributions of fibers, as these parameters control most of the transport properties of non-woven fibrous materials, 5 and therefore play a central role in the description of their sound absorbing characteristics. 6 In this work, we introduce a simple reconstruction procedure of a random fibrous medium.…”

The effects of compression on single and multiphase flow in a model polymer electrolyte membrane fuel cell gas diffusion layer

“…The most frequently used permeability relation in studies of porous medium is the Kozeny-Carman (K-C) equation, which is based on the idea of a porous medium being comprised of many tortuous capillary tubes [40]:…”