Metal Foams as Passive Thermal Control Systems

Abstract

Solid–liquid phase change in porous media occurs in many practical applications such as thermal energy storage, freezing of moist soils, and manufacture of metalmatrix composites. Of particular interest in this chapter are thermal energy storage units with thermal conductivity enhancers (e.g., metal foams) for transient thermal control of electronics. Here, the phase change material (PCM) impregnates a metal foam. The latent heat of the PCM serves to absorb the heat generated by the electronics, while the metal foam helps transport heat from the heat source into the volume of the PCM and helps utilize the PCM more effectively. It is important to understand the flow, heat transfer and phase change in these systems to better design phase change energy storage systems for electronics cooling. Melting and solidification of pure materials coupled with natural convection in the liquid melt has been studied extensively over the years (Sparrow et al., 1977, Gau and Viskanta, 1986, Jany and Bejan, 1988a). A detailed review of the literature on solid–liquid phase change heat transfer is given in Yao and Prusa (1989). Solid/liquid phase change processes in porous media have also received wide attention as they have many practical applications. Beckermann and Viskanta (1988) performed a combined experimental and numerical investigation of phase change occurring in a porous medium. Experiments were performed in a square enclosure with glass beads saturated with gallium. In their mathematical model, they assumed local thermal equilibrium between the glass beads and gallium. Their numerical results, which showed reasonable agreement with experiments, revealed that the solid–liquid interface shape was profoundly influenced by natural convection in the