Analysis of carbon foams by finite element method

The bulk properties of a porous medium are difficult to determine analytically, particularly for the case of high concentration of non-spherical pores, or when the porous material is anisotropic or non-homogeneous. Models that predict thermal conductivity of porous medium often use an empirical parameter to account for the effect of pore shape and material microstructure on the conduction process.; The purpose of this work is to develop a greater understanding of porous medium by developing finite element model (FEM) of carbon foams. The foam model is constructed by specialized solid modeling software using interconnected spherical and elliptical pores and then transferred to a general-purpose finite element analysis (FEA) software for analysis. The thermal conductivity result is obtained in the form of a non-dimensional effective thermal conductivity. The effective thermal conductivity is then evaluated by comparing the results of the analytical and numerical models.; The results show that a simple semi-empirical or analytical model with a constant empirical parameter (conduction parameter) cannot accurately predict the thermal conductivity of foams over the full range of porosity. The effect of the pore size and shape on the "conduction parameter" is presented. The "conduction parameter" is estimated for the entire range of porosities and its variation is obtained for different pore sizes and diameters.; The results show that the empirical conduction parameter used by many investigators depends on the influence each pore has on the neighboring pores, especially at higher porosities when the pores become interconnected. The effect of the struts and node structure of the carbon foams, pore shape and distribution, as well as their anisotropy on the thermal conductivity of carbon foam is studied.; This work also includes discussion of experimental studies to determine the thermal conductivity of various forms of graphitic carbon foam by the flash diffusivity method. A theoretical and numerical model is used to examine the effect of the filler epoxy on the experimental results. The experimental data is combined with the FEM analysis to determine detailed thermal properties of the foam microstructure.