With the increasingly strong implementation of energy-saving policies around the world, building energy-saving requirements are gradually increasing. In addition to the low-emissivity coated insulated glass that is being promoted continuously, a new type of inert gas filled with argon, helium, and other inert gases have appeared in the middle layer. insulated glass. Compared with air, inert gas has high density and low thermal conductivity, so it can slow down the heat convection of the intermediate layer and reduce the thermal conductivity of the gas, thereby reducing the heat transfer coefficient of the insulated glass and helping to improve the thermal insulation performance of the insulated glass. energy saving effect.
Filling the inert gas into the intermediate layer is beneficial to improve the thermal insulation performance of the insulated glass, but the type of inert gas filled, gas concentration, concentration retention rate, etc. have an impact on the improvement of the thermal insulation performance. LIJIANG Glass researches the application and quality control of inert gas in insulated glass from the aspects of performance comparison of different inert gases, the relationship between gas concentration and thermal insulation performance, and test of inert gas concentration and concentration retention rate.
1. The application of inert gas of insulated glass
Inert gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), which are colorless, odorless, non-toxic, gaseous single atoms Molecules, in the zero groups of the periodic table, the outer electrons are saturated and the activity is very small.
1.1 Performance comparison of different types of gases
Inert gases used for insulated glass are argon, krypton, and xenon. Their common features are stable performance, inactivity, higher density than air, and lower thermal conductivity. The densities of these three inert gases are 1.78 kg/m³, 2.86 kg/m³, and 4.56 kg/m³ (the air density is 1.29 kg/m³ under the same conditions) at 0°C and 101.325 kPa, respectively, and the thermal conductivity is 0.0163 W/(m·K), 0.0087 W/(m·K), 0.0052 W/(m·K) respectively. (the thermal conductivity of air is 0.0241 W/(m·K) under the same conditions.
Among the three gases, argon is the most abundant in the air. Argon accounts for about 0.93% of air by volume fraction, making it one of the most widely used and one of the cheapest inert gases on the market. The argon-filled insulated glass is UV resistant without affecting the light in the room. The content of krypton in the air is 1.14×10-4%, its stability and reactivity are similar to argon, and its thermal efficiency is 1/3 higher than that of argon, but it is more expensive. Xenon is the least content of the five rare gases in the air, with a content of only 0.09×10-4%. The stability and reactivity of xenon gas are also similar to argon gas, and the thermal efficiency is 1/2 higher than that of argon gas, but xenon gas in the natural state is very rare and the purification price is high.
The comparison of the physical properties of the three gases relative to the air, as well as the influence on the heat transfer coefficient of the insulated glass with the same configuration under the same inflation content, are shown in Table 1.
Table 1 The comparison between properties of different noble gases
|Gas type||Content in the air/ %||Density/kg*m-3||Thermal Conductivity|
|Heat transfer coefficient/W（m*K）-1 (6mm white glass+12mm+6mm white glass) insulated glass|
From the above comparison, the following conclusions can be drawn:
(1) The density of argon, krypton, and xenon is higher than that of air, and the thermal conductivity is lower than that of air, which is beneficial to greatly improve the heat transfer performance of insulated glass.
(2) The thermal efficiency of krypton and xenon is 1/3 and 1/2 higher than that of argon respectively, that is, to achieve the same heat transfer coefficient requirements under the same gas content, the insulated glass interlayer filled with krypton and xenon can only be 2/3 to 1/2 of the thickness of the argon-filled insulated glass interlayer.
(3) When the intermediate layer of insulated glass is filled with argon, the heat transfer coefficient is reduced by 5.96% compared with the case where the intermediate layer is air, the effect of filling with krypton and xenon is more obvious, and the heat transfer coefficient is reduced by 7.99 compared with the case where the intermediate layer is air. % and 9.26%.
The above three kinds of inert gases can significantly improve the heat transfer performance of insulated glass. Among them, argon has a high content in the air, and the inflation cost is low. With the advantage of the high-cost performance, it has become the most widely used gas for insulated glass inflation; krypton gas The extraction cost is relatively expensive compared with argon, and it is not widely used in the architectural glass industry. It is only used when the thickness of the insulated glass interlayer is small but the heat transfer performance is high; the content of xenon in the natural state is very rare, and the price of purification It is very high, so even if the heat transfer performance of insulated glass is better than that of argon and krypton, it is rarely used in the production of insulated glass.
1.2 Relationship between gas concentration and thermal insulation performance
It can be seen from the above discussion that argon has become the most widely used gas for insulated glass due to its outstanding cost-effectiveness. The following will discuss the influence of the gas concentration on the performance of the insulated glass through the comparison of the heat transfer coefficient in the case of different contents of argon gas inflated by three different configurations of the insulated glass. The different configurations of insulated glass are (4 mm white glass + 12 mm gas layer + 4 mm white glass), (4 mm online Low-E Glass+ 12 mm gas layer + 4 mm white glass) and (4 mm offline Low-E +12 mm gas layer+4 mm white glass). The heat transfer coefficient of each glass was calculated under the condition that the concentration of argon gas was increased from 0 to 100% and every 5%. The results are shown in Figure 1.
Figure 1 The influence of Inflating Concentration on Heat Transfer Coefficient of Insulating Glass
From the above results we can get:
(1) The higher the argon concentration, the smaller the heat transfer coefficient of the insulated glass and the better the thermal insulation performance.
(2) Under the same argon concentration, the improvement of the heat transfer coefficient of the coated glass is more obvious than that of the ordinary insulated glass.
At present, in the architectural glass industry, it is generally considered that the initial inert gas content of the gas-filled insulated glass should not be less than 90%, considering the effect of aeration to improve the thermal insulation performance of the insulated glass and the service life of the gas-filled insulated glass.
2.The quality evaluation method of gas-filled insulated glass
Filling the intermediate layer of insulated glass with inert gas helps to improve the energy-saving effect. The higher the concentration of the inert gas, the better the improvement effect. Whether the gas-filled insulated glass is filled with inert gas, the gas concentration, and the gas retention rate are the keys to evaluating the quality of the gas-filled insulated glass. Inert gas is colorless and odorless. How to determine the quality of gas-filled insulated glass through relevant detection methods is the focus of the required research. At present, there are three methods for the analysis and detection of noble gases: high-pressure electric spark method, oxygen paramagnetic method, and gas chromatography.
2.1 High voltage spark method
2.1.1 Detection principle
The high-voltage spark method is to penetrate the glass and the intermediate gas layer through the high-voltage spark generated by the equipment and activates the plasma of the noble gas molecules to emit radiation waves. Through emission spectroscopy, the instrument collects photons for analysis. The spectrum thus measured is compared with the data of the internal standard of the instrument to determine the inert gas concentration inside the glass.
2.1.2 Application of the method
This method is a non-destructive testing method, which can repeatedly detect the content of argon and krypton in the insulated glass, and will not cause any damage to the insulated glass, nor will it affect the subsequent use of the glass. It is suitable for laboratories and automated insulated glass. Inflatable plate press processing production line and engineering site inspection. At present, the equipment is mainly a Gasglass Handheld type instrument of Finland Sparklec Co., Ltd. The instrument is easy to carry, simple and fast to operate, as shown in Figure 2.
Figure 2 The gasglass Handhel instrument to test the initial concentration of argon gas filling 1
Based on the principle of the high-voltage spark method, it also has certain limitations. Electric sparks cannot pass through thicker laminated glass and low-E coated glass, so this method is useless for products such as double low-E coated insulated glass and thicker double-laminated insulated glass. And this method is more sensitive to the influence of background light, so it has higher requirements on the background environment during the test.
At present, the high-voltage electric spark method is adopted by the American standard ASTM E 2649—2009 "Standard Test Method for Determining Argon Concentration in Sealed insulated glass Units Using Spark Emission Spectroscopy", but based on the limitations of the test principle and method, the standard is only for the content of argon. The insulated glass of less than 70% is tested, and only the initial gas content of argon in the insulated glass is detected.
2.2 Oxygen paramagnetic method
2.2.1 Detection principle
The magnetic susceptibility of oxygen is hundreds of times higher than that of ordinary gases, and the magnetic susceptibility of mixed gases depends almost entirely on the amount of oxygen contained. The method utilizes the paramagnetic properties of oxygen to determine the oxygen content according to the magnetic susceptibility of the mixed gas, thereby calculating the content of the inert gas in the mixed gas. The relative magnetic susceptibility of some gases is shown in Table 2.
Table 2 The Relative Magnetic Susceptibility of Partial Gas
|The relative magnetic susceptibility||+100||+43.8||+6.2||-0.42||-0.61||-0.12||-0.59||-0.37||-0.57||-0.4|
2.2.2 Method application
This method is destructive. The test sample is the gas in the middle layer. When sampling, it is necessary to remove the outer layer of sealant, and then use a syringe to pass through the aluminum strip and enter the middle layer to extract the gas sample. The method is only suitable for quality inspection in laboratories and production lines, and not suitable for an engineering field test. This method is simple and convenient to operate, but the test accuracy is slightly worse than the other two methods, and it can only measure the content of inert gas in the gas of the intermediate layer of insulated glass, and the type of inert gas cannot be determined. This method is currently adopted by the international industry standard "insulated glass", which is used to test the initial gas content and gas sealing durability of insulated glass. Before the test, the inert gas analyzer is calibrated using dry air with a determined oxygen concentration and argon or krypton with a purity of more than 99.99%. Initial gas content To test 3 pieces of insulated glass, insert the syringe into the middle layer of insulated glass, push and suck twice, and inject 20 mL of gas sample into the equipment for testing. The initial gas concentration of the 3 samples should not be less than 85 %. The object of the gas sealing durability test is 3 pieces of insulated glass that have undergone the accelerated durability test. The test method is the same as the initial gas concentration. After the accelerated durability test, the inert gas content of the insulated glass shall not be less than 80%.
2.3 Gas chromatography
2.3.1 Detection principle
Due to the differences in properties and structures of the tested substances, the distribution coefficients of their components between the two phases are different. When the sample is brought into the chromatographic column by the carrier gas, the components are repeatedly distributed between the two phases. Although the flow rate of the carrier gas is the same, the adsorption or dissolving capacity of each component is different in the stationary phase, resulting in the running speed of each component on the chromatographic column. different. After a certain time of flow, they will be separated from each other, to achieve the effect of separation, and flow out of the chromatographic column into the detector in sequence. After the amplification of the electronic signal, the chromatographic peaks of each component are depicted on the recorder or chromatographic data processor. . According to the different retention times and peak area of each chromatographic peak, qualitative and quantitative analysis of each component of the sample can be made.
2.3.2 Method application
The test sensitivity and precision of this method are higher than the other two methods, and it can analyze nanogram-level samples, but it is only suitable for laboratory testing, not suitable for production quality control and field testing. This method requires a large investment in equipment and complicated operations and requires a tester with a professional background to perform the test. This method is currently adopted by the EU standard EN1279-3:2002 to test the gas concentration and gas leakage rate of insulated glass. The test of gas leakage rate requires extremely high precision, and the gas loss is calculated in milligrams, so only gas chromatography can meet the test requirements.
The whole process of gas leak rate testing of insulated glass is very complicated. After the accelerated durability test, the test sample is put into a sealed system of an "annular container". The internal size of the system is only slightly larger than that of the insulated glass, leaving a certain amount of residual gas around the glass. The whole system is placed at a constant temperature. in the measurement environment. During the test, there is always a working gas (helium) flowing in the system. When the insulated glass leaks out of the insulated glass due to the thermomechanical stress generated by the accelerated durability test, it can be captured and collected by the working gas. And transfer it to a gas chromatograph for accurate analysis and testing of inert gas content.
(1) insulated glass filled with inert gas has attracted more and more attention as a new product of building energy saving and environmental protection. At present, argon has become the most widely used inert gas due to its high-cost performance. Filling the insulated glass with a certain content of argon can improve the thermal insulation performance and sound insulation performance of the insulated glass.
(2) Among the three testing methods for the performance testing of inert gases in insulated glass, gas chromatography has the highest testing accuracy and can meet the testing requirements of gas leakage rate, but it is only suitable for laboratory testing; high-voltage electrical spark method equipment It is easy to operate, can meet the requirements of production quality control and engineering field testing and can be non-destructively tested, but the scope of application is limited, and it cannot meet the needs of high-end products such as double-coated hollow and double-layer hollow, as well as gas leakage rate testing requirements; oxygen paramagnetic The test process of the method is relatively simple and is suitable for production quality control and laboratory testing, but the test accuracy is low and cannot be used to characterize the type of inert gas.
(3) At present, the application of inflatable insulated glass in some developing countries is still in its infancy, and there are no published relevant product standards and method standards for the performance of inflatable insulated glass. Developed countries in Europe and the United States have formulated relevant standards for gas chromatography, such as the American standard ASTM E2269-2005 and the European standard EN 1279-3-2002, which respectively stipulate the gas chromatography method for the detection of inert gas concentration and inert gas leakage rate. The gas leakage rate is one of the most important properties of gas-filled insulated glass. Only gas chromatography can meet its test requirements. Therefore, LIJIANG Glass believes that the establishment of gas chromatography for inert gas analysis will play a very positive role in the popularization and application of gas-filled insulated glass.