Numerical Calculation On Effective Thermal Conductivity Of Fouling Based On The Finite Element Method

Fractal was first proposed by Mandelbrot and created a mathematical branch to explore the complex forms of nature,it is a geometry which takes the irregular geometry as the study object,to deal with the non smooth and irregular shapes and phenomena with self similarity and no characteristic length.Fractal theory and its application have been developed rapidly in the recent20 years,and more and more disciplines are introduced,greatly promoted the development of various subjects.It solves many problems which cannot be solved by traditional theories and methods,provides a new means for modern scientific research.The paper gets fouling samples under different working conditions by plate heat exchangers cooling water dynamic fouling simulation system,and SEM of particles fouling is filmed.Based on the fractal theory,fractal dimension application is written by MATLAB mathematical platform,and fractal dimension of particles fouling is calculated.And change rule between fractal dimension and various parameters is found.Image-Pro Plus 6.0 is applied to calculate and analyze pore characteristic parameters of particles fouling,and change rule between the equivalent thermal conductivity of fouling and various parameters is summarized.Through the ANSYS to write APDL language to establish three-dimensional network model of fouling pore,by changing the parameters of the model,in order to achieve the purpose of the research on micro porosity and macro fouling resistance.The obtained data were compared with those obtained by the steady-state plate method,linear fitting by Origin software.Finally,the linear relationship between fouling resistance,equivalent thermal conductivity and other parameters is obtained,provide some reference value for reducing fouling resistance and increasing thermal conductivity.The results show that fouling has fractal characteristics with two important characteristics of fractal characteristics: self similarity and scale invariance;Therefore,the surface fractal dimension can be used to quantitatively characterize the morphology of rough surface.The effective thermal conductivity of fouling decreases linearly with the increase of porosity,and increases with the increase of the pore size under the same porosity.Under the same porosity,the influence of the pore size change on the effective thermal conductivity of fouling is relatively small.However,under the same pore size the effect of porosity change on the equivalent thermal conductivity of fouling is larger.Fouling is a complex porous medium,heat is not only transmitted by solid frame,but also by internal complex pore.Using MATLAB to classify the microstructure of fouling,to extractthe characteristic parameters.Finite element method was used to simulate the microscopic characteristics of fouling,to calculate fouling equivalent thermal conductivity change in different characteristic parameters and a method for calculating the equivalent thermal conductivity coefficient of heat transfer surface is proposed,opens up a new way for the further study of the complex heat transfer process.