Flow and thermal performance of graphite foam dimpled fin heat exchangers

Graphite foam is one kind of favorable materials in thermal engineering applications because of its high thermal conductivity and large specific surface area. However, there is an associated high flow resistance in the graphite foam resulting from the porous structure property. In order to reduce the flow resistance and enhance the heat transfer, dimpled fins could be applied in graphite foam heat exchangers. In this paper, the flow characteristics and thermal performance of graphite foam dimpled fin heat exchangers have been investigated numerically through three-dimensional simulations of fluid flow and heat transfer in graphite foam dimpled fin channels. The local thermal non-equilibrium model has been applied to analyze the thermal performance of the graphite foam dimple fin (porous zone), and the Forchheimer extended Darcy's law has been employed to consider the air pressure drop through the porous graphite foam. Moreover, the SST κ-ϵ turbulence model has been used to capture the turbulent flow characteristics outside the graphite foam region. The details of the fluid flow and heat transfer over the dimple fin are presented. The results show that the graphite foam fin with two sides dimple presents the highest values of the normalized Nusselt number (between 2.4 and 4.6) and overall thermal performance factor. Furthermore, the graphite foam dimple fin provides higher effectiveness than the conventional aluminum offset fin, wavy fin and louver fin concerning energy saving.