Basic Cell Geometry for Modeling Flow in Metal Foam

Abstract

Open-cell metal foam is a class of modern porous media that possesses high thermal conductivity, large accessible surface area per unit volume and high porosities (often greater than 90%). The internal structure of the foam is web-like that produces a complex flow field, including turbulence, flow reversal and mixing, when a fluid passes through it. All of these attributes make metal foam a very attractive core for many applications, e.g. heat exchange, filtration and reactors. The rather complex and intrinsically random architecture of the foam is virtually impossible to capture exactly. In this paper, we present a unit cell geometrical model that can be used to study transport inside the foam. In particular, the unit cell is used to study the flow filed and pressure drop inside commercial foam. The Navier-Stokes equations are solved directly and velocity and pressure fields are obtained for various approach velocities using COMSOL. The details of the modeling process are given in this paper. The pressure drop results are compared to the Forchheimer prediction and to experimental data, from which the permeability and form drag coefficient can be calculated. The commercial foam that was used in the experiment had 10 pores per inch, and porosity of 91.2%. Air was forced to flow inside the foam using an open-loop wind tunnel. Good agreement between the modeling and experimental results are obtained, within the velocity range of the study. The results are encouraging and lend confidence to the modeling approach, which paves the way for investigating other phenomena inside the foam, e.g., heat transfer.