Convective heat transfer in graphite foams with complex structures

Along with recent advances in electronic packaging, high performance computer processors require more efficient devices for dissipating the high heat fluxes. The use of highly conductive porous media has emerged as an effective cooling method due to its large internal contact surface area which enhances convection at the pore level. In this study, graphite foams developed at Oak Ridge National Laboratory, USA, are used to enhance heat transfer. Initial studies performed by other investigators showed that the extended surface area also results in very high pressure drop for fluid flowing through the graphite foam. This paper presents a numerical and experimental study of convection heat transfer in graphite foams with different structures which are designed to reduce pressure drop. The non local thermal equilibrium model is adopted in the fluid and solid energy equations. The numerical results which are validated by experimental data show that the inlet air flow partially penetrates the designed foam walls and the rest of the air flows tortuously through slots in the structure. Flow mixing is observed in the free stream area inside the structures, which is absent in block graphite foam. This indicates that better convection can be obtained by these structures due to their low flow resistance and high flow velocity. The pressure drop in the designed graphite foam is also found to be significantly lower than that in solid block graphite foam.