Impacts Of Liquid Phase Distribution On The Effective Thermal Conductivity Of Organic Closed-cell Insulation

The application of organic closed-cell thermal insulation materials plays a key role in energy conservation and emission reduction in my country.Affected by operating conditions,water vapor infiltration and condensation will occur in the material,resulting in degradation of its thermal insulation performance and energy waste.The thermal conductivity of organic closed-cell thermal insulation materials is a key thermophysical parameter,which is of great significance to the study of its influencing factors and changing laws.This thesis proposes a multi-scale equivalent thermal conductivity model combined with the liquid phase distribution to analyze the influence of the liquid phase distribution shape on the thermal conductivity of the material caused by the fine microstructure parameters,and provide a reference for the optimization of the adiabatic systerm.Taking phenolic foam as the research object,this article first uses Fluent to build a liquid phase distribution model at the pore scale of the material,and compares it with the simulation results of Surface Evolver.Based on this,an improved multi-scale equivalent thermal conductivity model combining liquid phase distribution is proposed,and the model results are verified by experimental data.The constructed improved multi-scale equivalent thermal conductivity model was used to analyze the influence of the liquid phase distribution on the thermal conductivity of the material,and to establish optimized structural parameters.Finally,the feasibility of adjusting the material structure parameters to change the thermal conductivity is explored through experiments,in order to verify the single-objective optimization results of the model.The study found that: i)Based on the liquid phase distribution model,increasing the porosity,and reducing contact angle,the closed-open pore volume ratio can increase the critical saturation of the material and improve the thermal insulation performance.ii)Compared with the model that does not consider the change of the liquid phase distribution shape,the refinement of the liquid phase distribution shape can make the prediction of the equivalent thermal conductivity closer to the experimental value;iii)Under different saturations,the equivalent thermal conductivity decreases with the increase of porosity and relative offset ratio,and increases with the increase of contact angle and pore size.The degree of influence of various factors on the thermal conductivity varies with the change of saturation;the effect of closed-open pore volume ratio on the equivalent thermal conductivity shows the opposite trend at high and low saturation due to the change of liquid phase distribution.In the characterization voxel scale,the influence of the liquid phase distribution is mainly reflected in the low saturation region,while on the macro scale,the influence of the liquid phase distribution is weakened.iv)Taking the reduction of equivalent thermal conductivity as the optimization goal,the optimal structural parameters of phenolic foam when the optimal equivalent thermal conductivity is 0.0294W/m-K are calculated as porosity 0.95,closed-open cell volume ratio 8.495,closed cell pore diameter 0.027 mm,contact angle 0.525,the relative deviation ratio is 0.059.v)In the experiment,some structural parameters of the phenolic foam material can be adjusted to a certain extent by changing the stirring speed and foaming temperature.Based on self-made samples,the thermal conductivity measurement under dry and wet conditions,experimental test results and simulated values Have a certain similarity.However,due to the difficulty of precise control of the structural parameters of the self-made samples,it is impossible to verify the optimized structure.