The Study On Tetrahedron Model Of Porous Metal Foam

Porous metal foam is widely used in high efficiency heat exchanger,energy saving and environmental protection because of its large specific surface area,high thermal conductivity and excellent heat transfer enhancement function.At the same time,the research on the flow and the heat transfer of metal foam in porous media has attracted more and more attention.The structure of metal foam in porous media is very complicated,so that the process of heat transfer and heat transfer process intricately complex.It is impossible to determine the position of grid nodes and the real porous media especially in the numerical calculation of two-energy equation.Aiming at these characteristics of porous metal foam and the problems existing in the literature,a physical model of geometrical rules similar to that of true porous metal foam is proposed.The structure parameters and related physical parameters of the model is determined based on the consistency of flow and heat transfer.A tetrahedral model which is similar to the metal foam is established,and the relevant representative element volume is put forward.Based on the fractal theory foundation and criterion,the porosity and permeability of real porous media are obtained by the fractal theory.Based on the structural characteristics of the tetrahedron,the porosity and surface porosity are analyzed.The effectiveness of the surface porosity expression is discussed and compared with other models.The expression of the permeability of the tetrahedron model is presented.According to the principle of consistency,that the physical characteristics of flow and heat transfer represented by the constructed model are equal to or almost the same as those of the real porous medium,the structural parameters of the model are equal to the important structural parameters of the real porous media,the relationship between the real porous media and the tetrahedral model is established,so as to determine the structural parameters of the model.At the same time,the permeability of the tetrahedron model is compared with that of other scholars,to discuss the validity of the expression of the permeability of the tetrahedron model.The equivalent thermal resistance of the model is analyzed according to the structural characteristics of the tetrahedron.The equivalent thermal conductivity area and the equivalent coefficient of thermal conductivity are deduced from the thermal resistance uniformity.Theequivalent coefficient of thermal conductivity of metal foams are calculated by experimenting the thermal resistance of metal foam samples.At last,we summarize the analysis of the whole paper,and put forward some problems to be studied.