Research On Thermal Conductivity Of Porous Insulation Materials After Pressure Deformation

The most important parameter of the insulation material is the thermal conductivity,and the thermal conductivity directly determines the performance of the insulation material.Many scholars have conducted research on the thermal conductivity model of thermal insulation materials.The heat conduction model is mainly divided into two categories: 1.The Hasselman model improved from the series-parallel heat conduction model;2.The fractal heat conduction model obtained from the fractal theory.Insulation material undergoes deformation due to external forces during service,which will change the insulation performance of the insulation layer.Deformation of the insulation during service includes compressive deformation of the insulation during initial service and creep deformation during subsequent service.After undergoing deformation,the thickness of the insulating layer is reduced,and the internal structure changes,resulting in changes in its thermal conductivity.However,the existing heat conduction model is not able to describe the change of the heat conduction model in the process of deformation.Therefore,in the process of deformation it is very necessary to study the heat conductivity change law of heat insulation layer.The thermal conductivity of the porous insulation material is related to the thermal conductivity of the matrix,the thermal conductivity of the dispersed phase,the porosity,the average diameter of the cells,the circularity of the cells,and the temperature.This article consider to the most important factors,They are the thermal conductivity of the matrix,the thermal conductivity of the dispersed phase,the porosity,the average diameter of the cells,and the cell roundness.In this article other factors are not considered.The thermal conductivity,mechanical properties and mesostructure of thermal insulation materials have strong connection,so the mesostructure of the materials is first studied.In this paper,40kg/m3,60kg/m3,and 80kg/m3 insulation materials were selected to make observation specimens.Microscopy images were taken using a microscope and microscopic images were analyzed in Image J software to obtain the average pore size and circularity of the cells.At the same time,density methods are used to obtain the porosity of different density materials.According to the original parameters of the insulation material obtained,the two-dimensional model of the insulation material was established through Matlab software,and numerical calculation models of different types of insulation materials were obtained.Deformation calculations are performed in Abaqus software.Image J software was used to extract the structural parameters of the calculated deformed cloud image,and the regular relationship between deformation variables and meso-structure parameters was analyzed.At the same time,the elastic modulus of the matrix will affect the regularity between the deformation and the meso-structure parameters.Therefore,the influencing factors of the matrix elastic modulus are also used in the regular relationship.According to the calculation results,it can be found that there is a difference between the deformation variable and the porosity and the average pore size.For the quadratic relationship,the shape variable and the roundness have a one-time function.Based on the relationship between thermal conductivity,thermal conductivity of matrix,thermal conductivity of dispersed phase,thermal conductivity of porosity,roundness,and average pore size,a thermal conductivity model(insulation material thermal conductivity model under deformation conditions)is established to include the tangible variables and the influencing factors of matrix elastic modulus..This model can describe the variation of thermal conductivity of insulation materials under different deformation variables.The article designs and manufactures experimental devices based on Fourier's heat conduction law.Measure thermal conductivity of insulation materials under different compression deformation conditions and different creep deformation conditions.At the same time,comparing the calculated values of the thermal conductivity model with the measured values of the experimental device,it is found that the thermal conductivity model is well-matched,indicating that the established thermal conductivity model can describe the variation law of the thermal conductivity of the thermal insulation material under different deformation variables,and further illustrate the adoption of simulation methods.The relationship between the resulting deformation and the mesostructured parameters is correct.According to the uniaxial compression test of the heat insulation material,the force-displacement curve of the heat insulation material can be obtained,and the standard stress-strain curve can be obtained through conversion of the formula.The stress-strain constitutive equation of the porous media was selected to fit the experimental values of the stress-strain curve.It was found that the fitting effect was good,indicating that the constitutive equation can describe the compression deformation law of the thermal insulation material.At the same time,the creep experiment was conducted using an experimental device to obtain the creep-time curve of the insulating material.The modified time-hardening model was selected to fit the experimental data,and the fitting effect was good,indicating that the constitutive equation can describe the law of creep of thermal insulation materials.Combining the two constitutive equations with the thermal conductivity model of the thermal insulation material under deformation conditions can describe the variation law of the thermal conductivity of the thermal insulation material under different pressures.