X-ray microtomography scans of FiberForm are used to create microstructure geometry for incorporation within DSMC simulations of coupled oxygen diffusion and gas-surface chemistry in the presence of a blowing pyrolysis gas.
However, small variations in fiber size and angle bias can combine to give +30% uncertainty when comparing with experimental permeability data. Numerical uncertainty is determined to be within 2% if sufficiently large portions of the microstructure are included in the computation. DSMC results for permeability of FiberForm are validated for a range of pressures (transitional flow conditions) to agree with experimental measurements.
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An artificial fiber-microstructure generation code FiberGen is used to create triangulated surface geometry representative of FiberForm® (FiberForm) material. DSMC results for permeability are validated with computational fluid dynamics (CFD) calculations and theory, for simple porous geometries under continuum flow conditions. Micro scale simulations are performed of flow through porous (pyrolyzing) thermal protection system (TPS) materials using the direct simulation Monte Carlo (DSMC) method. in Chemical Vapor Infiltration (CVI) or filter clogging simulations. They are easy-to-use tools for large-scale numerical simulations of mixed-mode gas flow, eg. Finally, the dimensionless friction factors related to Knudsen diffusion, binary diffusion and viscous flow have been found to be correlated between each other, regardless the flow direction or the type of fibrous media. Accordingly, this work proposes useful extensions of these known correlations towards lower values of porosity. porosity are in agreement with fibrous filters literature values, that are available for pore volume fractions above 55%. The reported tendencies of the mass transfer coefficients vs.
An excellent agreement has been found for Darcian permeabilities and for Knudsen diffusivities, when taking the mean solid chord length as a characteristic length scale. pressure drop experiments and numerically with X-ray computerized micro-tomography (μ-CT), image processing and image-based computations. Permeation of gases in fibrous preforms of C/C composites has been studied with various degrees of infiltration, between 60% and 12% pore volume fraction, both experimentally with steady-state flow vs. Finally, diffusive tortuosities of a fibrous material are computed by applying the discussed numerical methods to 3D images of the actual microstructure obtained from X-ray computed micro-tomography. We discuss the upscaling of pore-resolved simulations to single species and multi-species volume-averaged models. We show that for particle methods, the surface representation significantly affects the accuracy of the simulation for high Knudsen numbers, but not for continuum conditions. These numerical methods include a finite-volume method for continuum conditions, a random walk method for all regimes from continuum to rarefied, and the direct simulation Monte Carlo method.
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In this work, we present numerical methods suitable for large scale simulations of diffusive transport through complex microstructures for the full range of Knudsen regimes. The data from these DNS are then used to close material’s macroscale transport models, which rely on effective material properties. Advances in X-ray micro-computed tomography (μ-CT) imaging provide the geometry of the material at the microscale (microstructure) thus enabling direct numerical simulation (DNS) of transport at the microscale. The diffusive tortuosity factor of a porous media quantifies the material’s resistance to diffusion, an important component of modeling flows in porous structures at the macroscale.
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