Vacuum Insulation Panel Preparation And Thermal Performance Research

Vacuum insulation panel（VIP）is a new type of thermal insulation material,and in recent years,its excellent thermal insulation performance has received more and more attention.However,in the process of building application,VIP is easy to be broken and leaky,which causes the degradation of heat insulation performance and the decrease of service life due to the increase of internal pressure,and other problems have hindered its development and application.In order to improve the thermal insulation performance and service life of VIP when it is broken,this paper proposes a unit encapsulated vacuum insulation panel.The unit raised barrier films and unit encapsulated vacuum insulation panels were prepared using silica aerogel glass fiber mats as core materials and vacuum blistering,vacuum compression and heat sealing processes.The microstructures and properties of the unitary raised barrier films and core materials were analyzed by scanning electron microscopy,specific surface area/pore size analyzer,thermal weight loss analyzer,X-ray diffractometer,and differential scanning calorimeter.In this paper,Ansys finite element software is used to simulate the changes of vacuum unit width and width between vacuum units,the number of broken vacuum units,thickness,ambient temperature,and specification size to explore the change law of its thermal performance and to obtain the optimal design parameters of the unit encapsulated vacuum insulation panel.Based on the theory of total thermal conductivity calculation,combined with mathematical formulas such as Rosseland’s approximation method and Knudsen’s relation equation,the service life calculation model of total thermal conductivity change with time is established,and its influence on the thermal conductivity and service life of unit encapsulated vacuum insulation panel is studied by controlling the parameter changes of internal vacuum degree,core fiber diameter,ambient temperature,core moisture content and air absorbent.The main results of this paper are as follows:1.It was verified that the thermal stability of the laboratory-prepared unit-bulk barrier films was essentially the same as that of ordinary barrier films,with transverse and longitudinal breaking forces greater than the standard values of 30（N/15 mm）and 24（N/15 mm）,and transverse and longitudinal elongation at break greater than the standard value of 300%.The best heat sealing temperature of 165°and the best heat sealing time of 1.2s were determined for the unit bump barrier films.2.The simulation found that the reduction rate of the heat flux of the unit encapsulated vacuum insulation panel showed a gradually decreasing law as the thickness gradually increased,indicating that the effect of improving its thermal insulation performance by increasing the thickness would be weakened with the gradual increase of the thickness.The smaller the width of the vacuum unit,the higher the average heat flux of the unit encapsulated vacuum insulation board,and the worse the heat insulation performance.Vacuum unit design width must be greater than 5 mm,the maximum design width of the vacuum unit can be determined only according to the number of breakage requirements.The width between the vacuum unit should be less than 1mm,when the width exceeds 7mm,the unit encapsulated vacuum insulation board has failed.Unit encapsulated vacuum insulation plate inside and outside the ambient temperature difference is proportional to the heat flux,but the plate thickness increases,can reduce the effect of temperature difference on the heat flux.If in the working environment where the temperature difference is large,it is necessary to consider the effect of temperature difference to design the size specification of the unit encapsulated vacuum insulation plate.It is verified that when the unit encapsulated vacuum insulation panel is damaged,only the vacuum unit area where the damage is located increases the heat transfer,the other areas are still vacuum environment,and the overall heat insulation and thermal insulation performance is better.If the size of 200×200mm unit encapsulated vacuum insulation board can be broken 10 times,the size of 200×200mm ordinary type vacuum insulation board can only be broken 1 time.In contrast,the number of breakage of unit package vacuum insulation board is much higher than that of ordinary vacuum insulation board.3.By establishing the internal pressure and thermal conductivity calculation model,it is concluded that the relationship between the internal pressure and thermal conductivity of the unit-encapsulated vacuum insulation panel has two phases-linear phase and non-linear phase,which indicates that the change of thermal conductivity in the two phases needs to be combined to calculate its service life more accurately.It was found that the thermal conductivity of the vacuum insulation panel encapsulated in a unit without the addition of an aspirant increased about 4.6 times faster with time than that with the addition of an aspirant.This indicates that the addition of aspirant can reduce the rate of increase of thermal conductivity of the unit package vacuum insulation panel and thus extend its service life.The service life is 46 years when the temperature is 10℃,and only 7 years when the temperature is 80℃,which shows that the temperature has a great influence on the service life of the unit encapsulated vacuum insulation board,therefore,the service life of the unit encapsulated vacuum insulation board should be predicted taking into account its actual use environment temperature,otherwise it will bring a large error.Simulation calculations show that when the thermal conductivity is 0.008W·m^-1·K^-1and the fiber diameter is 20μm,the service life of the unit encapsulated vacuum insulation panel is only 9 years.When the thermal conductivity is 0.002W·m^-1·K^-1and the fiber diameter is 5μm,the service life of the unit encapsulated vacuum insulation panel can reach 59 years.Therefore,in the actual production,the thermal conductivity and fiber diameter of the unit encapsulated vacuum insulation panel should be reduced as much as possible to obtain a longer service life.The results of the study can provide reference for the optimization design and practicality of the unit encapsulated vacuum insulation panel.