Vacuum glass is a new type of deep-processed glass product, developed based on the principle of thermos flasks. The structure of vacuum glass is similar to that of insulating glass, but the difference lies in that the gas in the cavity of vacuum glass is extremely thin, almost approaching a vacuum.
Vacuum glass is made by sealing the edges of two flat pieces of glass, evacuating the gap between them and sealing the exhaust holes. The gap between the two pieces of glass is 0.3mm. Generally, at least one of the two pieces of vacuum glass is low-emissivity glass, which minimizes the heat loss through conduction, convection and radiation of the vacuum glass. Its working principle is the same as that of heat preservation and insulation of glass thermos flasks. Vacuum glass is the fruit of the collaborative efforts of multiple disciplines, technologies and processes, including glass technology and materials science, vacuum technology, physical measurement technology, industrial automation and architectural science.
Principle
In principle, vacuum glass can be compared to a flat-shaped thermos flask. The similarity between the two is that the interlayer of the two layers of glass is a vacuum with a pressure lower than 10-1pa, making gas heat transfer negligible. Both have low-emissivity films coated on their inner walls to minimize radiative heat transfer as much as possible. The differences between the two are as follows: First, vacuum glass used for doors and Windows must be transparent or light-transmitting. It cannot be coated with an opaque silver film like a thermos flask. Instead, it is coated with a different type of transparent low-emissivity film. Second, to transform a cylindrical or spherical thermos flask that can withstand balanced pressure into a flat plate, a "support" array must be set up between the two layers of glass to withstand approximately 10 tons of atmospheric pressure per square meter, maintaining a gap between the glasses and forming a vacuum layer. The spacing of the "support" array is designed based on the thickness and mechanical parameters of the glass plate, ranging from 20mm to 40mm. To reduce heat transfer caused 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 and 0.5mm, and the height is between 0.1mm and 0.2mm. Vacuum glass also has an even better function, which is sound insulation. Due to the vacuum layer, it cannot conduct noise, so vacuum glass can block out 90% of the noise.
Folding
Heat transfer mechanism
Due to their different structures, the heat transfer mechanisms of vacuum glass and insulating glass are also different. Figure 2 shows a simplified heat transfer schematic diagram. The heat transfer at the center of the vacuum glass is composed of radiative heat transfer and support heat transfer, in which the heat transfer of residual gas is ignored. Insulating glass, on the other hand, is composed of gas heat transfer (including conduction and convection) and radiation heat transfer.
It can be seen from this that to reduce heat transfer caused by temperature differences, both vacuum glass and insulating glass need to reduce radiative heat transfer. An effective method is to use glass coated with a low-emissivity film (LOW-E glass). Under the condition of taking into account other optical performance requirements, the lower its emissivity (also known as emissivity), the better. The difference between the two is that vacuum glass also needs to minimize the heat transfer of the lattice support as much as possible
The thermal insulation performance of vacuum glass is based on the principle of vacuum thermos flasks. The heat insulation effect of tempered vacuum glass V glass products exceeds that of a 1-meter-thick brick wall and is 4 to 6 times that of ordinary insulating glass. The U value (also known as the heat transfer coefficient or K value) is as low as 0.4 W/m ² ·K (reported by the European IFT laboratory).
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 decibels (reported by CTC National Inspection Group), while the weighted sound insulation of general insulating glass is around 28 decibels.
Using tempered vacuum glass V glass, even in airports, on elevated Bridges or beside main roads, the interior is as quiet as a library.
Note: The higher the weighted sound insulation quantity, the better the sound insulation effect. If the outdoor noise is 75 decibels, after using tempered vacuum glass V glass, the indoor sound will be 36 decibels (75-39=36), and in libraries, it is generally below 40 decibels.
The expected service life of tempered vacuum glass V glass can reach over 25 years. It features a high vacuum inner cavity, which makes gas heat transfer negligible. Meanwhile, it uses high-performance LOW-E glass to significantly suppress radiative heat transfer, ensuring that the heat transfer coefficient (U value) of V glass is as Low as 0.4W/(m ² ·K). Meanwhile, the thermal insulation performance of V-glass is 2 to 4 times that of double-glazed glass and 6 to 10 times that of single-pane glass. When used independently, it can meet the international passive house requirements for the heat transfer coefficient of doors and Windows.
