An Investigation on Fluid Flow in Fibrous Materials via Image-Based Fluid Dynamics Simulations

Abstract

While there are a large number of analytical studies dedicated to developing permeability equations for a 2-D and 3-D models of fibrous disordered structures, there are only few numerical work that compares these models with real counterparts. For the first time, we present a series of numerical simulations performed on real fibrous media obtained via Digital Volumetric Imaging technique. An efficient procedure is presented for reconstructing 3-D images from the 2-D images of real fibrous media and processing them (meshing them) for performing fluid flow simulations. Permeability values obtained from these simulations are compared with those obtained from analytical equations given in the literature. We also present two scale modeling technique to predict macro scale permeability of fibrous structures.

Second part of this thesis deals with unsaturated flow through the fibrous media. We start our study by computing the pore size distribution of typical hydroentangled nonwoven materials and present a theoretical model for their geometric pore size distributions based on Poisson line network model of the fibrous media. We also study connectivity of the pore space in fibrous media by computing and comparing the accessible and allowed pore volumes in the form of access function graphs. We also present a novel image-based technique to study the changes in the pore size distribution of a fibrous material exposed to compressive load.

A combined micro- and macroscale modeling is presented to simulate the fluid infiltration in fibrous media. The Richards’ equation of two-phase flow in porous media is used here to model the fluid absorption in un-saturated fibrous thin sheets. The required consecutive equations, relative permeability and capillary pressure as functions of medium’s saturation, are obtained via microscale modeling and long column experiment, respectively. The Richards’ equation together with the above consecutive correlations is simultaneously solved for fibrous media inclined with different angles. To validate our simulations, we compared our numerical results with those of our long column experiment and observed good agreement.