The appearance of high-quality vacuum collector tube is:
1. The surface of the vacuum collector tube is smooth and clean, and the tube body has no spots, air lines, scratches and scratches (this phenomenon will affect the thermal efficiency and beauty).
2. The film color of the vacuum collector tube is mainly blue and black, and the overall color difference is small. However, black does not mean that the quality of vacuum collector tubes is good, because some manufacturers often make the film layer pure black to cover up the noise. In fact, there is inevitably a certain error in the color of the vacuum collector tube, which does not affect the thermal efficiency of the vacuum collector tube.
3. The drying mirror of the vacuum collector tube is complete, bright and clean, and there is no blackening phenomenon.
4. At present, there are three best vacuum collector tubes on the market: high temperature tube, high efficiency tube and cold tube. The film layer of high temperature tube is longer than that of ordinary tube (about 1cm from nozzle). This kind of tube has high temperature resistance and strong attenuation resistance. When exposed to air at 400℃, the film will not age, fall off or change color. The film layer of the high efficiency tube is about 2.5cm away from the nozzle. This kind of tube has ultra-high absorption, small heat loss, fast temperature rise and high thermal efficiency. The advantages of high cooling tube are high thermal efficiency, rapid temperature rise, and less heat loss, and hot water is discharged as usual at -30℃. Consumers can choose different vacuum collector tubes according to different regions.
5. With naked eyes, the color of the inner tube of the vacuum collector tube is dark red, indicating that its metal bottom layer is copper. This kind of vacuum collector tube can also work normally under cold conditions, and can also produce hot water as usual at -30℃.
All-glass vacuum solar collector tube (hereinafter referred to as vacuum collector tube) is the core basic component of solar hot water system with the largest output, the widest application and the most prominent energy-saving effect in the solar photothermal field in China. Its performance is directly related to the thermal performance of the water heater. At present, there are many manufacturers and brands of vacuum collector tubes in China, with uneven technical level, large price gap and inconsistent propaganda caliber. So, how to judge the performance of vacuum collector tube?
On May 25th, 2005, the General Administration of Quality Supervision, Inspection and Quarantine and the National Standardization Administration jointly issued a new national standard "All-glass vacuum solar collector tube" (GB/T 17049-2005). The new standard has been implemented since June, 2005 165438+ 10/day, thus replacing the old standard (GB/t 1 7049-1997) Therefore, we can only judge the performance of vacuum collector tubes according to the newly promulgated national standards. Compared with the old and new standards, the main technical changes are as follows:
-Improve the photothermal performance of vacuum collector tubes and their materials.
-Technical regulations for vacuum heat collecting tubes with glass tubes with a diameter of 58 mm have been added.
-Increase the vacuum quality inspection of vacuum collector tubes.
-Increase the use of steel balls in mechanical impact tests.
1。 Solar transmittance
The new national standard stipulates that the solar transmittance of glass tube materials is ≥ 0. 89(AM 1 .5)。 This is for the glass named "borosilicate glass 3". 3 "is a high borosilicate glass material.
"Borosilicate glass 3. Average linear thermal expansion coefficient α (20℃ ~ 300℃) = (3. 3 0。 1) ×10-6k-1.We used to call it borosilicate glass 3. 3"。 Use "borosilicate glass 3. 3 "glass tube, its solar transmittance τ≥0. 89(AM 1 .5)。 "AM 1 .5" means that the air quality is 1. 5。
All manufacturers of vacuum collector tubes will say that the raw material they use is "borosilicate glass 3". 3"。 However, if the glass used for manufacturing the vacuum collector tube is not borosilicate glass 3. 3 ",or it contains too many other elements (such as iron), the color of glass will have other colors (such as green). The solar transmittance of the vacuum collector tube made of this glass material will be much lower than 0. 89(AM 1 .5), which seriously affects the thermal performance of the collector tube.
2。 Solar absorption rate and hemispherical emissivity
Solar energy absorption rate and hemispherical emissivity are the technical requirements of solar energy selective absorption coating.
The new national standard stipulates that the solar absorption rate α of the absorption coating is ≥ 0. 86(AM 1 .5), the same as the old national standard. Hemispheric emission ratio εh≤0. 080 (80℃ 5℃), and the old national standard (0. 09) reduced by 0. 0 1; For vacuum collector tubes, the thermal efficiency of collector tubes can only be improved under the conditions of high solar absorption rate and low emissivity. Therefore, these are two extremely important parameters.
At present, the manufacturing technology of multilayer Al-N/Al solar selective absorption coating is still widely used in the manufacturing of vacuum collector tubes in China. This technology was invented by Professor Yin Zhiqiang of Tsinghua University and his colleagues in 1984, applied for a national patent in 1985, and was approved in 1987 (patent number: ZL85 100 1424+0424).
The basic principle of this technology is to establish a magnetron sputtering system with a single cylindrical aluminum target in the coating machine. Dozens of glass tubes, which are the inner tubes of the collector tube, are loaded into the coating machine at one time, and the glass tubes revolve and rotate under the drive of the "planetary" mechanism. The vertical cylindrical aluminum target was placed in the center, and the aluminum bottom layer was deposited by non-reactive sputtering in argon, and then nitrogen with controllable flow rate was injected to prepare multilayer aluminum-nitrogen composite thin film materials as absorption layers.
This manufacturing technology called gradient Al-N and Al solar selective absorption coating has a solar absorption rate of 0. 93, the emission ratio is about 0. 05(80℃)。 This is the first time in the world that only one metal material is used to prepare the selective absorption coating of metal bottom layer and composite film material at the same time. The Sun Le Zijin series vacuum collector tubes produced by Tsinghua Sunshine Company with this technology have been tested by the National Center for Quality Supervision and Testing of Light Industry Glass Products, and its solar energy absorption rate α=0. 95(AM 1 .5); Hemispheric emissivity εh= 0. 050(80℃ 5℃)。