[China Glass Network] First, the origin of vacuum glass

Many friends already know that vacuum glass is based on the development of vacuum dewar, which is the principle of our household vacuum glass thermos, then let us first understand the past and present of Dewar.

In 1892, Professor James Dewar of the University of Cambridge invented the Dewar, a double-glazed container with two layers of glass walls covered with silver and then the air between the two layers of glass was removed to create a vacuum. Since the vacuum prevents convection and conduction heat dissipation, the silver coating prevents radiation from dissipating heat, so the temperature of the material in the Dewar is not easily changed. Based on this, he summed up two basic principles of vacuum insulation: eliminating most of the heat convection and conduction through high vacuum; reducing radiation heat transfer through high-reflection coating. This becomes the basic principle of high insulation performance of vacuum glass.

Along the road opened by Dewar, Zaller first proposed the concept of vacuum glass in his patent in 1913. Since then, since the 1980s, the world's research and development of vacuum glass has gradually become active. Since 1985, the Vacuum Glass Research Group led by Professor DDK Benson of the Colorado Solar Energy Research Institute has created many technical theories, ideas and laboratory data worthy of future generations. Based on these findings, the research team led by Professor R.E. Collins of the Department of Applied Physics of the University of Sydney further improved the process and prototyped it in 1989. Then, the world's first 1m×1m flat vacuum glass sample was introduced at the University of Sydney in 1993.

In 1994, Nippon Sheet Glass Co., Ltd. (NSG) purchased the patent right of the University of Sydney and officially produced vacuum glass products in 1997. In 1998, China's vacuum glass began to develop, but it was not until 2008 that China formulated the vacuum glass industry standard JC-T1079-2008 that the vacuum glass “Jiaoshan True Face” was quickly known by the Chinese.

Second, the main performance of vacuum glass

[Three heat transfer in vacuum glass]

Heat transfer is carried out in three ways: conduction, convection, and radiation.

1 heat conduction: heat from the higher part of the object along the object to the lower temperature part, called conduction. In gases, the heat transfer process tends to occur simultaneously with convection.

2 Heat convection: The process of tempering the temperature between the hotter and colder parts of a liquid or gas to make the temperature uniform. Convection is a unique way of heat transfer in liquids and gases, and the convection of gases is more pronounced than in liquids.

â‘¢ thermal radiation: body temperature due to its having emitted energy outwardly fa ability, heat transfer in this way is called heat radiation. Although heat radiation is also a way of heat transfer, it is different from heat conduction and convection. It can transfer heat directly from one system to another without relying on media. Thermal radiation emits energy in the form of electromagnetic radiation. The higher the temperature, the stronger the radiation.

[Insulation of vacuum glass does not dew condensation performance]

The vacuum layer in the middle of the vacuum glass reduces the conduction and convection heat of the gas to a low level so that it is negligible. Therefore, vacuum glass has better thermal insulation properties than insulating glass. The technical parameter for the excellent thermal insulation performance of vacuum glass is the heat transfer coefficient - U value, which means that the heat passes through the center of the glass regardless of the edge effect. Under steady state conditions, when the air temperature difference between the two sides of the glass is exceeded, the unit time passes. The unit of heat per unit area, U is: W / (m2 • K). The vacuum layer of the vacuum glass has no air, no water vapor molecules, the seal is extremely strict, and the thermal resistance is large, and no condensation will occur in the winter.

Remark: 0.8W/(m2•K) refers to general vacuum glass, not specifically V glass 0.4W/(m2•K).

[Insulation and noise reduction performance of vacuum glass]

The transmission of sound requires medium. Whether it is solid, liquid or gas, it can transmit sound. However, in a vacuum environment without medium, the sound cannot be transmitted. Therefore, the vacuum layer of vacuum glass effectively blocks the transmission of sound. Vacuum glass exhibits good sound insulation performance at low and medium frequencies. The weighted sound insulation at 100-5000 Hz (including low, medium and high frequency) is 2 dB higher than that of insulating glass; the weighting at 100-1000 Hz (including low and medium frequency) In the calculation of sound insulation, the vacuum glass weighted sound insulation is 4dB higher than that of hollow glass, and the laminated glass and vacuum glass have similar performance in the middle and low frequency, which are obviously higher than the insulating glass. Vacuum glass has a high sound insulation in the low frequency range. This is mainly because the four sides of the vacuum glass are rigidly connected, so that the glass has stronger deformation resistance and stiffness than other forms of glass. The sound insulation of the low frequency band is affected by the stiffness, and the greater the stiffness, the better the sound insulation performance. In the low frequency band, the sound insulation is slightly reduced as the frequency increases, which is the result of the combination of stiffness and quality.

Third, the U value, K value, R value of the vacuum glass

Vacuum glass has excellent thermal insulation properties and good sound insulation and noise reduction performance, and has been widely used at home and abroad. In contrast to the thermal insulation properties of vacuum glass, domestic and foreign industries use different expressions. China and Europe use K values, the United States uses U values, and some use R values. So what is the difference between the U value, the K value, and the R value?

The concepts and definitions of U and K values ​​are identical and are the physical quantities that measure the heat transfer performance of a material, ie the heat transfer coefficient. The U value and the K value of the vacuum glass are defined as the heat transferred to the other side per unit area per unit time under a certain temperature difference under the standard conditions. The metric units of U and K values ​​are both W/m2·K.

However, the U and K values ​​are not exactly the same, except that the boundary conditions required by the respective test standards are different. The test value of China's K value is China's GB10294 standard. The European K value is based on the European EN673 standard. The US U value is based on the US ASHRAE standard. The US ASHRAE standard divides the U value test conditions into winter and summer. .

The test conditions for the three heat transfer coefficients are compared as shown in the following table:

Therefore, the same piece of vacuum glass, using different standards of measured heat transfer coefficient, has different results in terms of values.

European and American countries are accustomed to using imperial units, and the English unit of heat transfer coefficient U value (or K value) is BTU/h·ft2·°F.

The conversion relationship between the metric unit and the imperial unit of the heat transfer coefficient (U value or K value) is:

1 BTU/h·ft2·°F=5.678 W/m2·K or 1 W/m2·K=0.176 BTU/h·ft2·°F

European and American countries are accustomed to using the thermal resistance (R value) of glass to compare the thermal insulation properties of different glass materials.

The thermal resistance value R is used to reflect the ability of the insulating material to block heat from passing through. The greater the thermal resistance value R of the material, the stronger its ability to prevent heat from passing through, and the more suitable it is as an insulating material.

The thermal resistance value R and the heat transfer coefficient U value (or K value) are inversely related to each other, namely:

U=1/R or R=1/U

The metric unit of the thermal resistance value R is m2·K/W, and the imperial unit is: ft2·h·°F/BTU.

The following table lists the metric, imperial and corresponding thermal resistance values ​​R (imperial) of several U-value data:

U value and R value of Randy vacuum glass products

Note: T - tempered glass, L - Low-E coating, V - vacuum layer, A - air layer

Fourth, all tempered vacuum glass

With the wide application of vacuum glass, how to give vacuum glass safety performance has become a big problem that has long plagued the glass industry. In response, Luoyang Randy combines vacuum glass and tempering technology, and integrates unique vacuum glass manufacturing technology. Tempered vacuum glass - Randy "V-glass" came into being.

(1) Complete tempering:

V-glass is a truly all-tempered vacuum glass. The unique low temperature sealing technology is used to completely preserve the high strength and impact resistance of tempered glass. The stress distribution on the V-glass surface is uniform, and the stress at any point exceeds 90 MPa, which fully meets the stress requirements of the tempered glass.

(2) Real energy saving:

The thermal insulation performance of V glass is 2-4 times that of insulating glass. With a high vacuum chamber, the gas heat transfer can be neglected. At the same time, high-performance Low-E glass is used to greatly suppress the radiation heat transfer, and the heat transfer coefficient (U value) of V glass is as low as 0.4W/(m2·K). At the same time, V glass insulation performance is 2-4 times that of insulating glass, 6-10 times that of single glass. It can meet the requirements of international passive room for door and window heat transfer coefficient when used independently.

(3) Long life:

V-glass life expectancy can be more than 25 years. The use of flexible sealing material, in the environment with large temperature difference between indoor and outdoor, weakens the shearing force of the sealing area of ​​the glass plate, and overcomes the sealing failure problem of the brittle sealing material under the same conditions. At the same time, it is equipped with a high-efficiency getter, which can maintain the high vacuum of the glass cavity for a long time, and greatly reduces the failure phenomenon such as performance degradation in various harsh environments.

(4) The structure is light and thin:

V glass is lighter and thinner than insulating glass. In the case that the U value is much better than the three-glass two-chamber insulating glass, the thickness of the V-glass is only one quarter of it, and at the same time, the weight of the V-glass per square meter is reduced by more than 12 kg. At the same time, V-glass uses less Low-E glass, and the glass is more transparent, with excellent lighting.

(5) ji to the dew point:

The V-glass mechanism eliminates the internal condensation phenomenon. Compared with the condensation problem caused by the temperature difference between the inside and the outside of the insulating glass, the V-glass in the inner cavity is in a high vacuum state, which eliminates the internal condensation phenomenon. At the same time, the excellent thermal insulation capacity makes it impossible for condensation to appear on the inner surface of the glass even if the outdoor temperature drops to minus 70 °C.

(6) Effective noise reduction:

V-glass has a significant effect on the sound insulation of medium and low frequency noise with strong penetrating power. According to the ratio of professional weighted sound insulation, the noise of 75 decibels outdoors can exceed 36 decibels, which is far superior to the standard of 29 decibels of insulating glass.

(7) Any environment:

V glass is not affected by the area of ​​use, altitude and installation angle. The high vacuum of the V-glass cavity makes it impossible for the lumen to expand or contract even if there is a large difference in altitude between the production site and the place of use. At the same time, when the V-glass is used horizontally or obliquely, the heat transfer coefficient is constant, and it can be installed on the top of the building, the inclined roof, etc., to ensure energy-saving benefits.

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