On the effective thermal conductivity of a three-dimensionally structured fluid-saturated metal foam

A geometrical effective thermal conductivity model of a saturated porous me tal foam was developed, based on the idealized three-dimensional basic cell geometry of a foam, the tetrakaidecahedron. This geometric shape results f rom filling a given space with cells of equal size yielding minimal surface energy [1]. The foam structure was represented with cylindrical ligaments which attach to cubic nodes at their centers. The relative geometrical leng ths were calibrated with experiments [2]. It was found that the model estim ated the effective thermal conductivity very well for these experimental co nfigurations. It was shown that changing the fluid conductivity has a relat ively small effect on increasing the effective thermal conductivity. For an aluminum foam (k = 218 W m(-1) K-1) with 95% porosity in vacuum, the three -dimensional model predicted a k(eff) of 3.82 W m(-1) K-1. Using air as the saturating fluid (k = 0.0265 W m(-1) K-1) increased the thermal conductivi ty to 3.85 W m(-1) K-1. and water (k = 0.613 W m(-1) K-1) increased the the rmal conductivity to 4.69 W m(-1) K-1. This shows that despite the high por osity of the foam, the heat conductivity of the solid phase controls the ov erall effective thermal conductivity to a large extent, a fact that must be dealt with in the foam manufacturing process if specific ranges of the foa m effective conductivity are desired. It also implies that an accurate repr esentation of the contribution of the solid portion of the foam to the effe ctive thermal conductivity is needed in effective conductivity models. Deta iled expressions for the foam effective thermal conductivity were derived i n the course of this work and are reported in this paper. (C) 2001 Publishe d by Elsevier Science Ltd.