Monte Carlo determination of radiative properties of metal foams: Comparison between idealized and real cell structures

Metal foams are being widely adopted in a number of applications relevant to heat transfer, in which many include thermal radiation as the predominant heat transfer mode. Radiative characteristics of porous media are determined either by analytical modeling or by experiments.The aim of the present study is to evaluate the feasibility to substitute the real structure, more complex and computationally expensive, with the simpler and lighter ideal foam representation. The radiative heat transfer in foams is investigated using home-made Monte Carlo Ray Tracing codes. The geometry of the real microstructure of a metal foam is obtained by employing X-ray computed tomography (XCT). The actual 3-D structure is imaged, from which the total porosity, surface to volume ratio and size of a representative elementary volume for thermal analysis are determined. Results from the tomographic structures are compared to computer-generated Kelvin and Weaire-Phelan foam structures.Numerical results obtained for the real and ideal geometries are compared. The agreement is good, especially when accounting for the effect of the ligament shape. The good agreement between the results obtained with reference to the Weaire-Phelan convex ligament structures and those for real structures, both in terms of extinction coefficients and scattering phase functions, suggests that such idealized structures can estimate with good accuracy the parameters for equivalent homogeneous media on the basis of the porosity and the specific surface area.