| Based on the principle of vacuum heat insulation,Vacuum Insulation Panel tries to achieve this effect by taking advantage of vacuum degree to the greatest extent.It fills the bag with porous material with the lowest thermal conductivity known to people.The targeted product in this article was the VIP with thermal conductivity less than 1.5mW/(m·K).This kind of VIP tried to lower pore size of the core material to extend the service life of VIP.The study carried out in this article is based on(1)thermal insulation principle of VIP with low thermal conductivity,(2)the factors which may affect the thermal insulation performance,and(3)how fiber status affects the solid phase thermal conduction and service life of VIP between dry method and wet method forming processes.In order to achieve low thermal conductivity,low thermal bridge and long service life,the author here designed a kind of VIP comprised mainly of superfine glass wool core material,composite film made of materialized resin and multi-component getter.The author also had in-depth study on its service life expectation.This article put forward the technical road-map of producing wet method vacuum insulation panel by superfine glass fiber and sets up a system of wet method core forming process-by means of upright pulp-extraction,the pulp material can have separate layers and making wet method core material with separate layer structure,stable and directional distribution of fiber and small pore size by helping of super negative pressure forming process.Besides,this article set up the system of how fiber diameter,areal density and core material pore size affects each other in dry method forming process and the process flow of heat pressing on centrifugal glass fiber felt which means producing dry method core material with stable structure,high compression ratio and small pore size by taking control of parameters fibration and heat pressing.The author also put forward the idea of how temperature and pore size affects the service of vacuum insulation panel,reveals the law of how temperature affected other factors with effects on VIP surface life and finally gives the method of VIP life expectation.The laboratorial thermal conductivity had been lowered to 1.35mW/(m·K)which was a leading performance both in China and all around the world.The main results and are as follows:1.Molten glass flow rate and centrifugal running rate are important factors for fiber diameter.As the flow rate decreases,fiber diameter decreases in a nolinear way and fiber diameter and stability achieve the best condition when the centrifugal running rate is between 2700rpm/min and 3500rpm/min.Guiding air flow angle and areal density are two important factors for fiber felt distribution.When the guiding angle is between 40°and 60°,fiber felt has best distribution and when the areal density is between 1400g/m2 and 1600g/m2,fiber distribution can be controlled within ±15% and VIP thickness has the best homogeneity.When fiber length is between 10 mm and 40 mm,directional distribution angle decreases as the areal density increases.When areal density reaches 2000g/m2,directional distribution angle decreases dramatically.In heat pressing of dry method,pressure has more influence on fiber breakage then temperature.When temperature is controlled at 500±25? and the pressure is between 0.2MPa~0.5MPa,fiber has the best integrity and compression ratio gets its best condition.2.Replacing traditional blade beating method by high-speed air flow beating method which lowers the destruction of the fiber and integrity of the pulp material remains good.In the same beating time,fiber length decrease can be lowered by 50% and pulverization rate can be lowered by 2-3 times.It's a innovative method to use three-dimensional sectionalized extraction to gain graded pulp material in separate layers and results in different layers of pulverized,conglobate and dispersive pulp material.This is a technical breakthrough in core material forming process as pulverization and conglobation always involves.It uses multi-level negative-pressure dehydration to make wet method core material with multi-unit structure and realizes automate layering.When vacuum negative pressure is 0.6MPa and the forming rate is 60m/s,core material has an average directional distribution angle of 73.15°.Average pore size decreases and has concentrated distribution as the fiber diameter decreases.3.Fiber diameter has great influence in VIP's initial thermal conductivity.As fiber diameter increases: VIP thermal conductivity increases and fiber diameter shows cubic polynomial relationship when diameter is between 2.0?m and 7.0?m;VIP pore size increases and thermal conductivity increases faster if pressure goes up;core material content decreases in the same weight,meanwhile,core material shows worse ability to resist compression.This indicates that VIP density goes up as fiber diameter goes up.4.Film composition can affect effective thermal conductivity of VIP.With a layer of Al foil of 7?m,AF film has effective thermal conductivity which is several times higher than CF film.Besides,VIP thermal bridge changes in different VIP sizes-the bigger the size is,the smaller the thermal bridge will be.Sealing strength of the film mainly affects the sealing degree,bigger sealing strength results in better sealing degree and in better thermal insulation performance in the long run.If sealing strength is inefficient,it presents a fake sealing and low sealing degree which finally results in faster degradation rate.In vacuum environment,core material and film emit gases and there are more types and bigger volume of gases emitted from film.Getter can effectively absorb gases both from the inside and the outside.Multicomponent getter can effectively prevent the inside pressure from getting higher and obviously better than CaO getter.5.Environment condition has distinct effect on VIP aging performance.In high temperature and high humidity,VIP performance degrades faster.In refrigeration condition,it degrades much slower.Core material pore size is the key factor of its aging performance.In the same condition,bigger pore size results in faster degradation.When the pore size is between 30?m and 50?m,we will see the most obvious degradation rate.As for VIP with fixed composition and structure,annual degradation rates are different in different application temperatures.The relationship between degradation value and temperature is exponential.Therefore,VIP service life can be forecast by means of calculating its influence factors.The innovation points of this article are as follows:(1)The influence of the fiber row angle on the thermal conductivity of the vacuum insulation panels was found.The greater the angle of the shoot direction,the lower the content of the thermocline fiber in the core material,the lower the heat bridge effect of the solid heat conduction in the core,which can effectively prolong the total heat conduction along the glass fiber,so as to reduce the thermal conductivity of the vacuum insulation panels.(2)The influence mechanism of fiber diameter on the physical and aging properties of vacuum insulation panel was found.When the gas infiltrates into the vacuum insulation panels,the convection heat transfer tends to be obvious.The smaller of the fiber diameter,the ability to suppress convective heat transfer is stronger and the slower the thermal conductivity of the vacuum insulation panel is deteriorating in the same service cycle.(3)The method of airflow beating was invented.The length of fiber length in the slurry was better.The content of pulverized and reunion fibers in the core material was greatly reduced.The technical problems of mixing the powder and the agglomerate fibers in the core forming process were tackled.The lap and filling between the fibers were reduced and the thermal conductivity of the vacuum insulation panel was effectively reduced. |
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