Implicit Function Representation Of Porous Material And Numerical Simulation And Experiment Measurement Of Their Radiative Properties

Porous media is widely used in many fields as an ideal heat transfer material with characteristics of large specific surface area,low density and good heat absorption performance.Radiation characteristics are one of the main factors affecting the thermal performance of porous equipment.Especially in high temperature environment,radiation heat transfer can not be ignored,so it has been the focus of many scholars.However,in the numerical simulation of such research,the commonly used triangular surface porous structure characterization method have low precision,and the computer generated skeleton structure is also quite different from the actual porous medium.In this paper,the porous structures were generated based on the implicit function.In addition to using the existing implicit function expression to generate the regular porous structures,a method for generating the random porous structures which are similar to the actual porous structures is developed,and the structural parameters of the generated random porous structures can be flexibly controlled by adjusting the relevant parameters.Furthermore,the CT data of the actual foamed nickel samples were used to 3D reconstruct their respective skeleton structures.Then using the Monte Carlo ray tracing method based on function value,the self-edited program directly simulated the photon transfer process in the open-porous porous medium on the pore scale,and studied the relevant radiation characteristics of the porous medium under the condition of parallel incident light.The effects of different parallel light incident angles,porosity,pore density and diffuse reflectance of the skeleton surface on the absorption rate,reflectivity and backscattering energy distribution of the sample were analyzed.Subsequently,the backscattering distribution of three foamed nickel samples was actually measured,and the measurement results were in good agreement with the simulation results.Through simulation and experimental measurements,it was found that when the light is totally diffusely reflected on the surface of the skeleton,the backscattering energy of the porous medium to the parallel incident light is mainly distributed in the incident direction,and the peak energy is located near the incident direction,showing obvious retroreflection characteristics.And when the incident spot is large enough,the radiation characteristics of the regular and random porous structures have the same relevant parameters: the porosity and the diffuse reflectance of the skeleton surface are two important influence parameters,and the pore density has almost no effect.Moreover,the energy attenuation of the light inside the foamed nickel is roughly consistent with Lambert Beer's law,and the diffuse reflectance of the skeleton surface has no effect on the equivalent extinction coefficient.In addition,the implicit function-based porous structure generation method developed in this paper and the self-programmed Monte Carlo ray tracing calculation program have good practical value,and based on these methods,they can be used for further research after improving and optimizing.