Analysis Of Flow And Thermal Conductive Characteristics Of Porous Graphitic Foam

As a new kind of functional materials, porous foams exhibit low relative density,high surface area, high specific strength and permeability etc., when compared withconventional materials. Graphitic foam derived from mesophase pitch which representsone of the porous foams has a huge potential in national defense industry, aerospace,microelectronics and information industry for its unique properties such as high porosity,high thermal conductivity, heat-resistant, corrosion-resistant and so on, and has receivedwide attention and research. Most studies use experiments methods to investigate thepreparation process, performance and application of graphitic foam, and lack of theimpact of distribution of pore structure on graphitic foam’s properties has influencedfurther study.This paper studies the characteristics of flow (seepage flow) and thermalconductivity of graphitic foam materials. Based on its microstructure, models fornumerical simulations are set up, and influence factors affecting the material propertiesare discussed, furthermore, numerical results combined with experiments and theexisting theories and equations can provide theoretical prediction, verification and basisfor the study of porous foams in the further. The concrete content of this paper is asflowed:For the flow characteristics, this paper defines a equivalent particle diameter todescribe the geometric structure of porous foams based on the structure of a uniformpacked bed of spherical particles, and uses face-centered model and body-centeredmodel as a cell model for the whole flow regions to conduct the numerical calculations,and discusses the pressure variation in different foam models. Combined with theclassical Ergun equation, a dimensionless flow resistance equation for porous foams isset up, and the factors including porosity, pore arrangement and pore uniformity on theflow characteristics are discussed. And then, through self-designed and built test-bedexperiments, the flow parameters K and b of the graphitic foam are got from test results,and on an experimental basis, using the porous medium model in Fluent to simulate theflow characteristics in the graphitic foam, and the simulation results are compared withthe test results, verified the applicability of this simplified model for simulating the flowperformance of porous foams.For the aspect of thermal conductivity, firstly, homogeneity thermal conduction models are established for numerical simulations based on cell models, and the effectivethermal conductivity of different models is got. Compared with experiment results andsemi-empirical formula, it is found that for actual non-homogeneity porous foams, onlyporosity can not characterize the pore structure parameters of porous foam, porearrangement and distribution uniformity also affects the material thermal conductivity.Based on this, a randomness function about pore diameter is used in constructingnon-homogeneity thermal conduction models, and from the simulations results of thesemodels with random structure, it is found that apart from porosity, pore uniformity isalso one of the important factors of the effective thermal conductivity of porous material.And it is also point that the relative effective thermal conductivity of porous foammaterial can be expressed as power function of the macro-porosity and pore uniformity.