Forced convection in finned metal foams: The effects of porosity and effective thermal conductivity

Abstract

Metal foams are promising candidates for enhancing the thermal performance of heat exchangers due to their unique features such as high surface-area-to-volume ratio and stochastic orientation. However, limited heat dissipation in high porosity metal foams is found to be a significant constraint on the heat transfer enhancement. To overcome this issue, metal foam structures with fins were proposed. On the other hand, the enhancement of heat transfer obtained by the addition of fins is connected to the porosity and effective thermal conductivity of metal foams. This relationship needs to be considered in the design of the structures with finned metal foams properly. This study, accordingly, investigates the effects of porosity and effective thermal conductivity on flow and heat transfer in a channel with finned metal foams. First, a numerical model was established and validated with the experimental data in the literature. Next, the flow and heat transfer characteristics of metal foams with different porosities and effective thermal conductivities were investigated under different fin configurations. The numerical results show that the addition of fins does not yield a considerable increase in the friction factor, and heat transfer shows a considerable increase up to the addition of a certain number of fins. When the fin number is further increased, the enhancement in heat transfer becomes relatively limited for all metal foams considered in this study. The effective fin number depends on the porosity and effective thermal conductivity. The results also show that the contribution of fins to the heat transfer in the parameter range considered in the study varies between 40-115% and 70–150% at the lowest and highest velocities, respectively.