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. KEY WORDS: viscous permeability, fibrous performs, fiber-reinforced composites, computer simulation, electrical conduction, molecular diffusion, experimental data