XMT-based direct simulation of flow and heat transfer through open-cell aluminum foams

Three aluminum foam samples of varying pore sizes -10 ppi, 20 ppi and 40 ppi - are CT-scanned using a commercial X-ray scanner at 20 micron resolution for measuring and comparing important heat transfer parameters such as effective thermal conductivity and Nusselt number. Small sub-samples from the resulting stack of images are processed to generate feature-preserving high-quality finite-volume meshes. It is observed that all three foam samples exhibit similar volumetric porosity (in the range ~91-93%), and thereby a similar thermal conductivity. For the domain sizes considered, the samples exhibit anisotropic conduction along the three coordinate directions of the mesh, which is attributed to the randomness of the structure and the small domain sizes considered. The values of average effective thermal conductivity are compared with a number of previous experimental and simulation results. Effective tortuosity for conduction along the coordinate directions is also calculated. Permeability simulations in the Darcy flow regime with air and water show that foam permeability is isotropic and is of the order of 10^-7 m². The resulting friction factor variation with Reynolds number is validated against published results. Nusselt numbers are also computed for this range of Reynolds numbers. The heat transfer results exhibit a dependence on the linear porosity, even though the corresponding volumetric porosity is the same for all the samples considered.