Study On Heat Conduction Of Unsaturated And Rough Surfaces In Porous Media Based On Fractal Theory

Porous media exists in all aspects of people's life,as a heat transfer enhancement material,and has significant advantages in many aspects such as heat preservation,heat insulation,filtration,etc.However,due to the complex structure of porous media and random distribution of internal pores,it is relatively difficult to study the internal heat transfer process of porous media.In view of the above problems,this paper simulates the internal structure of porous media through fractal theory and Monte Carlo method,which can well model the complex structure of porous media.Therefore,fractal theory and Monte Carlo method are of great significance for the study of heat transfer in porous media.The main research contents are as follows:(1)Analyze the internal structure characteristics of porous media.The fractal theory is used to construct the pore distribution on the cross section of porous media,and considering the pore structure characteristics of porous media with liquid phase,the cross section model of porous media with liquid phase is constructed.(2)The heat transfer process of unsaturated porous media was studied.By analyzing the internal heat transfer process of porous media,the heat conduction formula of porous media in wet unsaturated condition was deduced based on the fractal theory and Fourier law,combined with the relevant parameters and calculation formulas in the heat transfer process.(3)The data of heat transfer inside unsaturated porous media were simulated and compared with experimental data to verify the accuracy of the new theory,and the relationship between thermal conductivity coefficient and moisture content,porosity,heating time,maximum and minimum pore size ratio,fractal dimension and rough surface area was obtained.And explain the causes of these relationships.(4)The Monte Carlo method is used to generate random numbers to approximate the distribution of microconvex bodies on the rough surface of porous media.The two-dimensional and three-dimensional models of the rough surface are established by MATLAB.At the same time,the mathematical model of heat transfer on the rough surface of porous media is established according to the combination of fractal theory and Monte Carlo method.(5)Substituting relevant data into the mathematical model of rough surface generated by the fractal Monte-Carlo method,and then verifying the accuracy of the theory by experimental comparison,further analyzing the factors affecting heat transfer of rough surface and the change relationship between them.The results show that the influence of the phase transition in the porous media on the heat transfer process should be considered when studying the heat transfer in wet unsaturated porous media.In the study of heat transfer on rough surface,fractal Monte Carlo simulation was used to make the results closer to the real value,and there was a negative correlation between porosity and effective thermal conductivity.The moisture content is positively correlated with the effective thermal conductivity.The fractal dimension is negatively correlated with the effective thermal conductivity.At the same time,the thermal conductivity is also related to the heating time,the maximum and minimum aperture ratio,saturation and so on.This study can specifically reflect the heat transfer process in the porous media and the heat transfer of the microstructure of the rough surface of the porous media,which has a certain guiding significance for the heat transfer of the material with the microstructure of the rough surface.