Vacuum glass is a new typeGlass deep processingThe product is developed based on the principle of thermos bottle.Structure of vacuum glass andHollow glassSimilarly, the difference is that the gas in the vacuum glass cavity is very thin, almost close to vacuum.[1]
The vacuum glass is composed of two piecesplate glassSeal around, vacuum the gap and seal the exhaust hole. The gap between two pieces of glass is 0.3mm. Generally, at least one piece of vacuum glass isLow emissivity glass, so that the vacuum glassconductionThe heat lost by convection and radiation is minimized, and its working principle is the same as that of glass thermos bottle.Vacuum glass is the science of glass technology and materialsVacuum technology, physical measurement technology, industrial automation and building science, etctechnologyFruits of cooperation and cooperation of various processes.
In 1990Peking UniversityThe Department of Physics has taught for more than 30 yearsTang JianzhengCame to Australia as a visiting scholarUniversity of Sydney, began to jointly research flat vacuum glass with Professor R.E. Collins, who was then the director of the Department of Applied Physics of the university.After three years of efforts, in 1993, the world's first 1m × 1m flat vacuum glass sample came out.However, although the inventors are Tang Jianzheng and R.E. Collins, the patent right belongs to the University of Sydney.In 1996, the University of Sydney transferred the patent to the Japanese Plate Nitrite Glass Company, and the Japanese began batch production of vacuum glass the following year.
Vacuum glass is a new type of glass deep processing product, which is one of the few cutting-edge products with independent intellectual property rights in China's glass industry. Its R&D and promotion are in line with China's policy of encouraging independent innovation, as well as the energy-saving policy vigorously advocated by the country. It plays a great role in energy conservation and sound insulation, and has good development potential and prospects.
principle
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In principle, vacuum glass can be compared to a flat thermos bottle. The similarity between the two is that the interlayer of two layers of glass is a vacuum with air pressure lower than 10-1pa, which makes the heat transfer of gas negligible;The inner walls of both are coated with a low radiation film to minimize the radiation heat transfer.The difference between the two is that vacuum glass must be transparent or transparent when used for doors and windows. It cannot be coated with opaque silver film like a thermos bottle. It is coated with different kinds of transparent low radiation films;The second is to change from a cylindrical or spherical thermos bottle with balanced compression resistance to a flat plate. A "support" matrix must be set between the two layers of glass to withstand the atmospheric pressure of about 10 tons per square meter, so as to keep the gap between the glasses and form a vacuum layer.The spacing of the "support" square array is designed according to the thickness and mechanical parameters of the glass plate, and is between 20mm and 40mm.In order to reduce the heat transfer formed by the "thermal bridge" of the support and make it difficult for the human eye to distinguish, the diameter of the support is very small. The diameter of the support in the product is between 0.3mm-0.5mm, and the height is between 0.1mm-0.2mm.Another better function of vacuum glass is sound insulation. Since there is a vacuum layer that cannot transmit noise, vacuum glass can insulate 90% of the noise.
Heat transfer mechanism
Due to different structures, vacuum glassHollow glassThe heat transfer mechanism is also different.Figure 2 is a simplified heat transfer diagram. The heat transfer at the center of vacuum glass consists of radiation heat transfer and support heat transfer, in which the heat transfer of residual gas is ignored.The insulating glass is composed of gas heat transfer (including conduction and convection) and radiation heat transfer.
It can be seen that to reduce the heat transfer caused by temperature difference, both vacuum glass and insulating glass should reduce the radiation heat transferLow radiation filmGlass of（LOW-E glass）In consideration of other optical performance requirements, the lower the emissivity (also known as emissivity), the better.The difference between the two is that vacuum glass should be minimizedlatticeHeat transfer of supports,
The thermal insulation performance of vacuum glass is based on the principle of vacuum flask.The heat insulation effect of tempered vacuum glass V glass products is more than 1 meter thick brick wall, which is 4-6 times that of ordinary insulating glass. The U value (also called heat transfer coefficient or K value) is as low as 0.4 W/m2 · K (European IFT laboratory report).
The sound insulation and noise reduction performance of vacuum glass is based on the fact that sound does not propagate under vacuum conditions.The weighted sound insulation of tempered vacuum glass V glass reaches 39 dB (reported by CTC), and the weighted sound insulation of ordinary insulating glass is about 28 dB.
Using tempered vacuum glass V glass, even near airports, viaducts or main roads, the interior is as quiet as a library.
explain:Weighted sound insulationThe higher, the better the sound insulation effect.For example, the outdoor noise is 75 decibels. After using tempered vacuum glass V glass, the indoor noise is 36 decibels (75-39=36), and the noise in the library is generally below 40 decibels.
The expected life of tempered vacuum glass V-glass can reach more than 25 years. It has a high vacuum cavity, which makes the gas heat transfer negligible. At the same time, it uses high-performance Low-E glass, which greatly inhibits the radiation heat transfer, and ensures that the heat transfer coefficient (U value) of V-glass is as low as 0.4W/(m2 · K).At the same time, the thermal insulation performance of V glass is 2-4 times of that of insulating glass and 6-10 times of that of single glass. It can meet the requirements of international passive room on the heat transfer coefficient of doors and windows if used independently.
Sound insulation mechanism
The vacuum glass and insulating glass are completely different in structure and production. The insulating glass simply glues two pieces of glass together, with an air layer sandwiched between them. The vacuum glass is sandwiched between the two pieces of glass with a film support, so that the two pieces of glass can be completely fused in a high-temperature vacuum environment. The middle of the two pieces of glass is vacuum, and the sound cannot be transmitted in a vacuum state,Of course, because the vacuum glass supports become sound bridges, the vacuum degree cannot reach 100% vacuum, but these supports only account for one thousandth of the glass, and these are small sound bridges that can be ignored.
Product benefits
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1. Low carbon and energy saving
The vacuum glass relies on the special structure of the vacuum layer to effectively block the indoor and outdoor heat conduction. The heat transfer coefficient U is below 0.6Wm-2k-1, which can be as low as 0.3W/(m · K), similar to the wall.It can significantly reduce air conditioning power consumption and emissions of pollutants and greenhouse gases, and reduce environmental pollution.
2. Thermal insulation
The vacuum glass with proper shading coefficient can effectively control the solar heat gain and keep the room cool in summer;In winter, when the outdoor temperature is - 20 ℃, the internal surface temperature of vacuum glass is only 3-5 ℃ lower than the indoor air temperature, which can keep the indoor warm and comfortable.
3. Sound insulation and noise reduction
With the dense urban population andMeans of transportationWith the increase of, noise pollution is becoming increasingly serious, which directly harms people.The vacuum layer of vacuum glass can effectively block the transmission of sound, especially for medium and low frequencies with strong penetrability.
4. Keep away from condensation
Vacuum glass has super thermal insulation performance. In cold winter, even if the outdoor temperature drops to - 30 ℃, the temperature of the indoor glass surface is close to the room temperature, far higher than the condensation temperature.
5. Wide application
The interior of the vacuum glass is in a vacuum state, which is not affected by the ambient pressure, and is suitable for various altitudes;At the same time, the vacuum glass can maintain its excellent performance in all positions of the building, including the facade, slope and roof. There is no problem that the gas convection increases when the insulating glass is placed horizontally, leading to the performance degradation.
The product can be made into one sideSandwich structureIt can also be made into a double-sided sandwich structure. The thickness of EVA film (also known as EN film) is about 0.4 mm and 0.7 mm.The thickness of polycarbonate board is about 1.2mm.The additional glass plate is selected between 2.5mm and 5mm, and can also be usedTempered glass。vacuumsandwich glassAnother method is to fill glue in the middle of two layers of glass, and then through heating and drying, vacuum laminated glass can also be made, which is characterized by safety and anti-theft. At the same time, its heat transfer coefficient, sound insulation, wind pressure resistance and other properties are also better than vacuum glass, and the total thickness is relatively thin.As the thermal conductivity of glass and adhesive layer is large and their contribution to thermal resistance is small, the heat transfer coefficient of vacuum laminated glass is only slightly smaller than that of vacuum glass, but the sound insulation performance will be greatly improved.
2. "Vacuum+hollow" composite vacuum glass
This structure is equivalent to taking the vacuum glass as a piece of glass and then combining it with the additional glass plate to form a hollow. The thickness of the additional glass plate is generally 5 or 6mm tempered glass, which is placed outside the building. It can also be made into a double-sided hollow combination of "hollow+vacuum+hollow".
Such combination not only solves the safety problem, but also improves the heat and sound insulation performance.In particular, when the additional glass plate is also made of Low-E tempered glass, the heat transfer coefficient will be reduced.
When calculating this kind of composite glass, we should first realize in principle that in the temperature and temperature difference range we discussed, the wavelength of thermal radiation is 4 to 40 in the far infraredμM-band,Soda lime glassThe electromagnetic radiation in this band is basically opaque, so when calculating the radiant thermal resistance of more than three glasses, it is not necessary to consider the impact of the radiation through the first piece on the third piece, as long as it is calculated in sections and then added. Therefore, if the total thermal resistance of the "vacuum+hollow" combination is R combination, it can be written as: R combination=R+R hollow
Where R is the thermal resistance of vacuum glass
R hollow is the thermal resistance of hollow glass made of two pieces of glass with the same thickness as the additional glass plate
The calculated R combination only calculates the thermal resistance of one piece of glass, and the error is very small.
3. "Vacuum sandwich+hollow" structure
The heat transfer coefficient of this structure is similar to that of "vacuum+hollow", but this structure has the advantages of low heat transfer coefficient and safety. In addition, the thickness is thinner than that of "hollow+vacuum+hollow". Moreover, due to the asymmetry of both sides of the vacuum glass, the resonance of sound transmission is reduced, and the sound insulation performance is improved.
He once made a sample for a music teaching building in Beijing, which is of 6+0.38EVA+4L+0.15V+4+12A+6 structure, with a total thickness of 32.5mmTsinghua UniversityThe measured weighted sound insulation in the building physics laboratory is 42dBglass screen wallThe highest level of national standard weighted sound insulation is only 3dB.The heat transfer coefficient can be 0.7-0.9Wm-2k-1, which is determined by the selection of LOW-E glass.
4. Double vacuum layer vacuum glass
The total thermal resistance of this structure can be regarded as the sum of the thermal resistance of two pieces of vacuum glass. If it is a vacuum glass with the same structure, the total thermal resistance is twice that of a single vacuum glass, that is, R double vacuum=2R
Where R is the thermal resistance of single vacuum glass
It should be noted that the different positions of Low-E film in the structure do not affect the K value, but only affect the temperature distribution of the three pieces of glass in actual use.
The double vacuum glass has high thermal resistance, low K value and is very thin, which can be about 9mm thick, and can also be made into double vacuum layer sandwichSafety glassIt has great development potential.
new technique
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With the development of science and technology, new materials, new processes and new technologies continue to emerge, and the quality of vacuum glass itself will continue to improve.The production process and equipment will also be constantly updated, the output will continue to expand, and the cost will continue to reduce.The variety of combined vacuum glass will also increase.Research at home and abroad shows that for most areas, the heat transfer coefficient of building envelope should be at least 1Wm-2k-1. In the past, the heat transfer coefficient of 37 brick walls (with external mortar) with a total thickness of 390mm widely used was about 1.7 Wm-2k-1, and the heat transfer coefficient of 37 hollow brick walls (with external mortar) with a total thickness of 410mm was close to 1 Wm-2k-1.The heat transfer coefficient of various new walls can be reduced to 0.4 to 0.8 Wm-2k-1.And doors and windows are the major energy consumers of building envelope.The heat transfer coefficient of a single 5mm white glass is about 6.1 Wm-2k-1, which is more than 6 times worse than the wall. Figuratively, the energy consumption of each non energy saving window is equivalent to the energy consumption of a tens of watts long burning lamp over the years.More than thirty years agoThe first oil crisisAfter that, foreign scientists proposed to develop glass windows with heat transfer coefficient less than 1, called "Superwindows".The appearance of vacuum glass makes this idea easy. The appearance of double vacuum glass will make us enter the stage of "super vacuum glass window".
Fully tempered vacuum glass is an upgraded version of vacuum glass. It not only inherits all the characteristics of vacuum glass, but also has a great improvement in performance. Its main feature is that the glass used is fully tempered safety glass, which can be widely used in buildings, doors and windows of vehicles and ships, thermal insulation cabinets (such as display cabinets, refrigerated cabinets) and other needs to be transparentThermal insulation materialThe domain of.
Development trend
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Upgrading the consumption structure of residents, encouraging independent innovation of enterprises, new rural construction and urbanization process will ensure that the medium and long-term demand growth trend for glass products in the domestic market will remain unchanged.With the development of construction, automobile, decoration, furniture, information industry technology and other industries and the improvement of people's requirements for living space environment, functional processing products such as safety glass, energy-saving insulating glass have been widely used.plate glassThe supply and demand pattern and consumption structure are changing.
The development of the glass industry is connected with many industries of the national economy, and the glass industry plays a positive role in promoting the development of the entire national economy.Therefore, the 11th Five Year Plan also puts forward specific requirements for the development of glass industry.Various laws and regulations have also been promulgated to regulate the healthy development of the glass industry.In the new situation, the glass industry must change its growth mode and effectively adjust its industrial structure in accordance with the requirements of the Scientific Outlook on Development in order to promote the healthy development of the industry.
