Theoretical And Experimental Research On The Model Accuracy Improvement Of Effective Thermal Conductivity Of The Disperse System

Dispersion, the existence form of many materials and industrial products including semi-finished products, is formed by loose depositing of solid particles in gas phase or liquid phase. Its geometrical structure is special, which leads to the difficulty of exactly determining its effective thermal conductivity. The research of effective thermal conductivity of dispersion infiltrates a lot of science fields and includes many branches of learning. However, there are many kinds of dispersion materials with different characteristics and it is an immature subject up to now. The dispersion research has great theoretical meaning and wide application background. On the basis of domestic and foreign study, this paper studied the heat conduction in naturally deposited dispersion by means of theoretical model and experiments. A general heat percolation model to predict the effective thermal conductivity of disperse materials was presented. The agreement between the model predicting results and experimental results was well. Firstly, the specific characteristics and complexity of the dispersion geometrical structure play a decisive role in its effective thermal conductivity. Accurately describing the geometrical structure of dispersion is the premise of exactly predicting its effective thermal conductivity. This paper adopted fractal theory to describe the geometrical structure of dispersion. Compared with traditional method, the parameters used in this method are measurable and this method truly reflects the geometrical structure of dispersion. Secondly, by analogy with fluid flowing in porous medium and electric current conducting in random resistance network, the heat flow conducting in dispersion could be regarded as a kind of percolation process and the scaling law still holds water. So the general behavior of heat conduction in the mixture of two kinds of materials could be obtained from critical phenomenon. This paper corrected the error source of traditional renormalization group theory in two-dimensional and three-dimensional real space and used corrected renormalization group theory to determine the critical value of percolation and critical transport exponent. Thirdly, based on fractal theory and renormalization group theory, this study presented the full expression of heat percolation model to predict the effective thermal conductivity of dispersion. In addition, the model considered the contribution of radiative heat transfer to the effective thermal conductivity of dispersion in high temperature, which extended the model's temperature scope of application and decreased the model prediction error in high temperature. Moreover, by means of the theory of cut-out hot wire method to measure the thermal conductivity of materials, an experimental system was designed, corresponding data acquisition and data processing software was drawn up. The experimental system can be used to measure the effective thermal conductivity of dispersion in different circumstance temperature. The experimental results verified the rationality and accuracy of the heat percolation model. Also, being aimed at error source in the measuring process, this paper analyzed the uncertainty of experiments.