Research On Core/Whole Heat Transfer Performance And New Application Of Vacuum Insulation Panel

At present,vacuum insulating panel(VIP)has been widely used because of its excellent thermal insulation performance,but there are still some deficiencies in the research of VIP which need to be supplemented.In this paper,the heat transfer performance of VIP from core material to the whole body is studied and its service prediction is carried out with the dry glass fiber core material VIP as the research object.Firstly,the heat transfer model and heat transfer performance of VIP for dry glass fiber core material are explored.Secondly,the thermal bridge effect of VIP is evaluated by numerical method.Finally,the service performance of arc VIP for circular tube insulation structure is predicted.The SEM photos of VIP cores were processed and analyzed by means of histogram equalization and pixel matrix statistics.The porosity and average fiber diameter of VIP cores were 91% and 3.5 um.Porosity and average diameter of core material fibers are taken as structural parameters to be substituted into core material micro-heat transfer model and micro-heat transfer unit is generated.The structure generation and heat transfer statistical analysis of heat transfer unit are completed by Monte Carlo method.Solid phase thermal conductivity of core material with different porosity and average diameter of core material is obtained.RBF neural network was used to establish the relationship between the solid thermal conductivity of VIP core material and its porosity and average fiber diameter,and the empirical formula of solid thermal conductivity of VIP core material was obtained.Finally,the solid thermal conductivity of VIP core material was replaced by the solid thermal conductivity term in the calculation formula of thermal conductivity of VIP core material to obtain the complete formula for determining the thermal conductivity of VIP core material.The criteria for evaluating the thermal bridge effect of VIP are determined.The thermal bridge effect of VIP for dry glass core material was analyzed by thermal resistance network method,and twodimensional and three-dimensional thermal resistance network models were established.The heat transfer model of VIP is established by using two-dimensional thermal resistance network,and the influence of performance parameters and size parameters on the thermal bridge effect of VIP at constant temperature boundary is analyzed.The performance parameters are the thermal conductivity of VIP core material,and the influence of performance parameters on the value of VIP thermal bridge criterion is determined by exponential fitting.The size parameters are the thickness,length and barrier thickness of VIP.According to the analysis and comparison,the independent variables are converted to the thickness of VIP,the ratio of width to barrier thickness L,H.RBF neural network is used to determine the influence of L and h on the VIP thermal bridge effect criterion.The results show that the thermal bridge effect of VIP decreases slightly with the increase of thermal conductivity and the decrease of h,and decreases significantly with the increase of L.The evaluation interface of VIP hot bridge is designed by using the design module of MATLAB GUI.The thermal conductivity of the dry glass fiber core material VIP with AF barrier film was tested to verify the thermal bridge model.It was found that the thermal bridge effect of VIP with AF barrier film and thickness of 0.01-0.02 mm could be neglected under the size of 300mm×300 mm.The heat transfer formula in cylindrical coordinates and the dichotomy iteration method are used to calculate and design the external insulation structure(steady state)of VIP pipeline.The heat preservation effect of the design structure using VIP and not using VIP is compared by two ways: fixed thickness and fixed heat flux.When the thickness is fixed,the heat flux decreases by 10-15%,and when the heat flux is fixed,the total thickness of insulation layer decreases by 2.4-9%.The finite difference method is used to calculate the external thermal insulation structure and the internal temperature field(unsteady state).The thermal insulation effect of the designed structure using VIP and not using VIP is compared by using fixed thickness and fixed inner structure density.When the thickness of the missile is fixed,the internal temperature of the missile can reach 40 C by using VIP,and the other two structures can reach 47 C and 84 C respectively.When the inner density is fixed,the internal temperature of the missile can reach 48 C by using VIP,and the other two structures can reach 64 C and 74 C respectively.The use of VIP improves the thermal insulation performance of internal and external insulation structures and saves space,which has important engineering application value.