Modeling of convective heat transfer coefficient of graphite foam and effective young's modulus of short fiber-reinforced composite

The present work can be divided into two parts: (1) the analytical modeling on the overall convective heat transfer coefficient of porous graphite foam, developed at the Oak Ridge National Laboratory, and (2) the finite element analysis on effective Young's modulus of short fiber-reinforced composite. The present efforts focus on the relationship between the vital microstructural parameters (e.g., pore size, porosity, fiber aspect ratio, etc.) and overall properties (eg, convective heat transfer coefficient and effective Young modulus) of novel graphite foams and discontinuous fiber-reinforced composites

The graphite foam developed at the Oak Ridge National Laboratory is a promising candidate for the core material in heat exchangers. To develop graphite foams that exhibit high thermal conductivities, high convective heat transfer coefficients, and acceptable pressure drop across the foam, one must have a clear delineation of the interaction between overall properties and foam microstructure, which in turn, is related to the processing of foam. To this end, an analytical model is developed to explicitly include vital microstructural parameters such as foam porosity and pore size, and properties and free stream velocities of cooling fluids, and to predict the overall convective heat transfer coefficient as well as pressure drop of the graphite foam. The predictions agree well with experimental results.

Not a lot of analytical models are available for estimating the effective properties and the stress transfer in short fiber-reinforced or whisker composites. The most popular ones are shear-lag based models The validity of the predicted effective Yung moduli of short fiber-reinforced composites obtained by the modified shear-lag model is verified by the present finite element analysis In particular, the effects of fiber volume fraction and fiber aspect ratio on the effective Young modulus of short fiber-reinforced composite are examined. It is concluded that the modified shear-lag model generally provides very accurate estimates on effective longitudinal Young's moduli of short fiber- reinforced composites