Effects Of Thermal Radiation On The Effective Thermal Conductivity Of Metal Foams

As a novel structural and functional material, metal foams have been widely applied in aeronautical, astronautical, mechanical, and electromagnetic fields. During the engineering of metal foams, the thermal characteristic should be considered synthetically with other physical properties, so it is of great value to research the effective thermal conductivity (ETC) and the mechanism of heat transfer inside for their thermal properties prediction and engineering. There have been a lot of researches on the conductive and convective heat transfer in metal foams with the thermal radiation effects neglected. However, metal foams are applied at high temperature for many cases, the thermal radiation effects is intensive or even dominates the heat transfer. The thermal conduction-radiation coupling effects at high temperature and the special structure of metal foams make it difficult to predict and optimize the thermal properties at high temperature for the various and complex influencing factors. Therefore, the effects of thermal radiation on ETC are researched in this work.To analyze the mechanism of the heat transfer in metal foams, a simplified analytical model of thermal conduction-radiation coupled heat transfer is proposed. A set of dimensionless numbers based on which radiative heat transfer effects the ETC are derived by similarity analysis, and their physical significances, influencing law, mechanism are analyzed. The effects of porosity, cell size, temperature, emissivity and sample thickness on ETC are researched by simulating the conductive-radiative coupled heat transfer in metal foams based on simplified 3D models describing the structural characteristics of metal foams. And at last, the simplified analytical model is verified by comparing the influence laws of the dimensionless numbers with that of the 3D structural model.The results show that the ratio of thermal conduction to conduction is the main influencing factor on ETC, the boundary temperature and emissivity of pore surface dominate the temperature distribution and coupling intensity, the ETC grows as the increase of sample thickness, the temperature linear distribution assumption and Rossland diffuse approximation will bring relatively large errors. Large porosity and pore size make ETC more sensitive to the temperature. Moreover, the morphology should also be considered when predicting the ETC of metal foams. And the simplified analytical model can be used to analogically analyze the conductive-radiative coupled heat transfer in metal foams and the influencing mechanism of the various factors on the ETC.