Construction Of Thermal Network Model For Heterogeneous Materials And Its Study On Thermal Conduction

Heterogeneous materials not only retain the excellent thermal properties of each component,but also increase the thermal properties that the original component does not have.Heterogeneous materials play an important role in the traditional fields such as mechanical equipment,construction,rock and soil,as well as in the high-tech fields such as aerospace and automobile industry.In this paper,the thermal network model of heterogeneous materials is constructed,the thermal conduction characteristics of multiphase heterogeneous materials are studied.Firstly,several methods for solving and predicting the effective thermal conductivity of heterogeneous materials are analyzed.Under the condition that the volume fraction and the ratio of thermal conductivity of each phase change respectively,the variation trend of the effective thermal conductivity of classical models is obtained,and several classical models are compared.The finite element method for thermal conduction of heterogeneous materials is described,and combined with the finite element method,the model of thermal conduction network of heterogeneous materials with random distribution is established.This modeling method can be used for the construction of heterogeneous materials with random distribution and the prediction of heat transfer characteristics in thermal conduction.Secondly,two-dimensional and three-dimensional thermal conduction network models of two-phase heterogeneous materials are established respectively.By changing the volume fraction,spatial distribution and thermal conductivity of the two phases of heterogeneous materials,the variation law of the effective thermal conductivity of the system is obtained.The results show that two-dimensional and three-dimensional thermal conduction network models of two-phase have a region where the random distribution has little effect on the effective thermal conductivity of the thermal network,which is called the emergent region,in the emergent region,the thermal conductivity of each phase is close,the heat flux flows uniformly through each phase,the effective thermal conductivity shows a basically consistent trend,and the effective thermal conductivity is no longer affected by the spatial distribution of the two phases,the logarithmic mixed criterion is proposed to predict the effective thermal conductivity of heterogeneous materials.When the contrast of thermal conductivity between two phases is large,the effective thermal conductivity is greatly affected by random spatial distribution and volume fraction,the heat flux tends to flow through a certain phase,the effective thermal conductivity is controlled by the heat flux path,and further percolation phenomenon occurs.It is also found that the volume fraction of two-dimensional and three-dimensional thermal network models is different when the percolation phenomenon occurs.The proposed logarithmic mixing criterion is compared with experimental data to verify its correctness.The design of heterogeneous multiphase materials and the prediction of thermal response in thermal conduction are provided with new support by this method.Finally,the causes of the percolation phenomenon and the factors affecting the percolation threshold are analyzed,and based on the thermal conduction network model of two-phase heterogeneous materials,a three-phase random thermal network model is established,the variation of effective thermal conductivity of the system with the ratio of thermal conductivity of each phase is obtained by changing the parameters.The results show that the three-phase random thermal network also has an emergent region,which is similar to the two-phase random thermal network,and the effective thermal conductivity of the system in this region can also be solved and predicted by the logarithmic mixing criterion.The difference between a three-phase random thermal network and a two-phase random thermal network is that the heat flux path of a threephase random thermal network is more complex and the percolation phenomenon can occur separately in all phases.In this paper,the construction method of the thermal conductivity network model of heterogeneous materials and the method of solving and predicting the effective thermal conductivity of heterogeneous materials provide a new idea for the design of heterogeneous materials,the study and description of the emergent behavior and percolation phenomenon of heterogeneous materials provide a good reference for the study of thermal conductivity of heterogeneous materials.