Integrated micro x-ray tomography and pore-scale simulations for accurate permeability predictions of porous media

This study conducts pore-scale simulations and experiments to estimate the permeability of two different types of porous materials: metal foams and sintered copper particles with porosities of approximately 0.9 and 0.4, respectively. The integration of micro X-ray computed tomography with pore-scale computational fluid dynamics simulations develops a unique tool to capture the pore-scale geometry of porous media and accurately predict non-isotropic permeability of porous media. The pore-scale simulation not only results in improved prediction accuracy but also has the capability to capture non-isotropic properties of heterogeneous materials, which is a huge challenge for empirical correlations, volume averaged simulations, and simulations with simplified pore geometries. The permeability of air flow through 10-, 20-and 40-ppi aluminum foams (i.e., pore sizes of 2.54 mm, 1.27 mm, and 0.64 mm) are estimated to be 8.25×10-8 m2, 3.16×10-8 and 2.70×10-8 m2, respectively. Experimental measurements and pore-scale simulations estimated permeabilities of water to be 4.63×10^-11 and 5.95×10^-11 m², respectively, in a customized porous structure sintered from 200-µm copper particles. The pore-scale models, validated by experimental data, were applied to simulate anisotropic properties of the material along three orthogonal directions. The estimated permeabilities of the 10-ppi (pore size of 2.54 mm) aluminum foam are 8.2×10-8, 9.1×10-8, and 1.1×10-7 m2 along the X, Y, and Z directions, respectively. The estimated permeabilities of the sintered copper particles are 5.95×10-11, 4.00×10-11, and 5.78×10-11 m2 along the X, Y and Z directions, respectively. The predicted properties of porous media can be applied to volume-averaged models and obtain better accuracy. This research also investigates the size of representative unit, which is critical to balance the accuracy and computational cost of simulations. Results recommend that for porous materials made from regular-shaped particles (e.g. spheres), the representative unit should be generally larger than three times of the particle or pore size if the flow is laminar.