Anisotropy effects on convective heat transfer and pressure drop in Kelvin's open-cell foams

Open-cell foams have the potential to offer heat transfer enhancement in many applications, such as heat exchangers, solar air receivers, porous burners, thanks to their high heat transfer surface to volume ratio and to tortuosity, that promotes the internal flow mixing. Their microstructural transport features are affected by foam anisotropy, and could play an important role not only because manufacturing processes can stretch the cells along a preferential direction, but also because modern techniques allow for the customization of the foam cell shape. However, structural anisotropy in open cell foams has been scarcely investigated. In this paper, anisotropy effects on convective heat transfer and pressure drop in Kelvin's open-cell foams are analyzed. Since Kelvin's model is geometrically regular, anisotropy has been investigated by stretching the foam along three orthogonal directions, at equal cell volume. Governing mass, momentum and energy equations have been solved using a finite element method. Results are presented for different fluid inlet velocities and cell sizes along three orthogonal stretching directions. They show that anisotropy affects the velocity and temperature fields, and, consequently, the permeability, inertial factor and volumetric heat transfer coefficients.