| 其他摘要 | Due to their outstanding thermo-physical and mechenical properties, porous materials are widely used in every sections of the national product. As a relatively new type of structural and functional materials, the artificial porous materials, addition to their conventional applications, are arose increasingly interesting on their new potential utilizations in other fields. Reseashing the principles of fluid flow and other mass transport phenomena in porous materials are essential to their practical applications. In this work, the single phase fluid flow characteristics and the heat electricity transport principles in porous materials, mainly in three reticulated porous materials, are intensively investigated by computational simulation techniques with a small amount of experiments. Based on the tetrakaidecahedron skeleton structure model designed by computer, the conclusions can be drawn as follow:
The Reynold’s number sphere describing flow patterns transition from linear to nonlinear flow in porous material was obtained. Three flow regimes in porous media, including Darcy’s regime, Forchheimer’s regime and Froude’s regime, were visualized and discussed. Parameters, such as permeability, inertia coefficient, and friction factor, were obtained in order to describe the fluid flow characteristics of porous media. The influence of foam structure on the fluid flow characteristics was elucidated. Empirical correlations comprehensively reflecting the influences of parameters, such as porosity and pore diameter on permeability and inertia coefficient were fitted.
The effective thermal conductivity keff of three-dimensional （3D） reticulated SiC foams increases as the volume fraction f increases. However, there were no systematic changes detected in keff when the cell size and the cell models of the foam vary at a fixed volume fraction. The keff of SiC foams as a function of f was obtained. Compared the experimental results with the calculated ones, it indicated that the outcome can be widely applied in estimating the effective thermal conductivity of other foam materials. The calculated results indicated that the heat transfer in the foam is anisotropic, that is, the heat flux is superior to pass through the struts which parallel to the temperature gradient. The heat flux reaches to a relative high value at the node position.
Under the equal wall temperature boundary condition, the convection heat transfer coefficient of three reticulated foam materials increases with the fluid flow velocity, and decreases with the cell size. Existing a best match of cell size and volume fraction, it makes the convection heat exchange reached its highest effectivity. In the computing sphere, the foam with its cell size and volume fraction of 1mm and 22.8% has the lowest heat resistance under the same pump power. The velocity field and temperature field in the porous material are nonuniform, and have harmony with each other.
Similar to their thermal conductivity, the electrical conductivity of foam materials increases with the volume fraction. The influence of the cell size on the electrical conductivity is not obvious in foam materials. The calculated results agree well with the experimental results. By calculating the electrical conductivity of SiC foam in a whole range of the porosity, three correlations, which describe the relationship between the ratio electrical conductivity and the volume fraction, were derived from the mathematic fitting. After non-dimensionalizated, these equations can be widely applied in predicting the electrical conductivity of other foam materials with the similar structure. The calculated results indicate that the electrical current transfers is anisotropic in the foam, that is, the current is superior to pass through the struts which parallel to the electric field. The higher current density was obtained at the node position in the foam. |
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