At present, there are three series of all-glass vacuum tube solar collectors on the market: ordinary all-glass vacuum tube solar collector, heat-tube all-glass vacuum tube solar collector and U-tube all-glass vacuum tube solar collector. Three series of products. At present, the general type of all-glass vacuum tube solar collector is still mainly used. The structure and characteristics of the three series of products are introduced one by one.
Ordinary all-glass vacuum tube solar collector
1.Composition: vacuum tube, header, tailstock and bracket
There are two types of cross tubes and vertical tubes.Its power is relatively large, you need to reserve 4 square meters of copper core wire to install the water heater. In addition, because of the large power, a large amount of electric energy is consumed during the operation, although the internal components of the electric electric water heater can effectively save electric energy, but compared with the general electric water heater, some electric energy is wasted.
1.1 Vacuum tube construction: The vacuum tube is the core component of the all-glass vacuum tube collector and the engine of the entire solar system. Its performance determines the heating performance and life of the whole system.
Vacuum tube construction diagram
1.2 Vacuum tube material requirements: vacuum tube adopts borosilicate glass 3.3 (iron oxide content less than 5%; good thermal stability; low thermal expansion coefficient is 3.3×10-6/°C; good thermal shock resistance, heat resistant temperature difference is greater than 200°C;has high mechanical strength; good chemical corrosion resistance; has good optical properties, light transmittance ≥ 0.89)
1.3 Vacuum tube technical requirements:
a. material using borosilicate glass 3.3;
b. air drying performance parameters y ≥ 175m2•°C/ kW (when solar irradiance G ≥ 800W / m2, ambient temperature t between 8 ~ 30°C)
c. The sun exposure to the water temperature increased by 35°C
d. required solar radiation exposure ≤ 3.8 MJ / m2 (when the solar irradiance G ≥ 800W / m2, the ambient temperature t between 8 ~ 30°C)
e. average heat loss coefficient ≤0.9W/m2·°C
f. vacuum degree ≤5×10-2Pa;
g. thermal shock resistance should be able to withstand cold water below 25°C and hot water above 90 ° C alternately repeated 3 times without damage;
h. pressure shock should be able to withstand a pressure of 0.6Mp;
Anti-Hail requirements shall not be damaged under the impact of i. i. hail with a radial dimension of not more than 25 mm.
1.4 Vacuum tube coating technology
At present, there are two kinds of coating processes for vacuum tubes: gradient coating process and interference coating process. The interference coating process is a further development of the vacuum tube coating technology, with higher absorption rate and lower heat dissipation rate.
2.all-glass vacuum tube collector features:
the vacuum tube directly heats the water, the highest heat absorption efficiency; long life; the lowest cost . At present, 80% of the solar energy centralized water supply projects on the market use this series of products. This series of products has high requirements on the design, installation and construction of the system. If the design is improper or the installation is poor, the pipe burst will occur.
Heat pipe type vacuum tube type solar collector
The heat pipe type vacuum tube type solar collector is a new product developed on the basis of the ordinary vacuum tube collector. It has been widely used in some special fields.
1. heat pipe type vacuum tube type solar collector features
As shown in the above figure, the heat pipe is inserted into the ordinary vacuum tube, and the heat pipe is wrapped with the aluminum profile fin, and the aluminum profile fin is in contact with the inner wall of the vacuum tube to transmit heat. The heat pipe is a blind pipe that is closed at both ends. The processing technology is: using pure copper tube (pure copper content ≥ 99.99%, commonly known as oxygen-free copper) to inject distilled water, and vacuum separation and plugging. The distilled water has a very low boiling point under vacuum, and the heat transfer is carried out by the evaporation heat absorption and the condensation heat release of distilled water, and the heat transfer efficiency is high. However, since the vacuum degree of the heat pipe has a great influence on the heat transfer efficiency, the exhaust pipe (vacuum) of the heat pipe has strict requirements on materials and processes.
The material must use oxygen-free copper, and the oxygen-free copper core can prevent oxygen ions from penetrating into the pipe. Of course, the price of this material is also quite expensive, resulting in high cost of heat pipe products. Ordinary production processes are difficult to guarantee the quality of the heat pipe. The production environment and production equipment are very strict. Even a little hand stain will cause the vacuum to be difficult to guarantee. Once the vacuum is reduced, the heat transfer efficiency will be greatly reduced.
No leakage, stable system; high thermal efficiency; short life and high cost. The requirements for copper are strict and the production process is strict. The greater the angle between the collector and the ground plane, the higher the efficiency. The degree of vacuum in the copper tube is high, and once the air is leaked, the efficiency drops sharply until it fails.
U-tube type vacuum tube type solar collector
1:vacuum tube; 2:coated film layer; 3:U-shaped copper tube; 4:aluminum profile fin.
As shown in the figure above, the U-shaped copper tube is inserted into the ordinary vacuum tube, and the U-shaped copper tube is surrounded by the aluminum-type fin, and the aluminum-type fin and the inner wall are in contact with the vacuum tube to transfer heat. The U-shaped copper tube and the piping system, as well as the heat exchange coils in the water tank, form a closed loop and exchange heat through forced circulation of the medium.
Indirect heat transfer, pressure operation, no leakage of the explosion tube, high thermal efficiency, and arbitrary installation angle. However, packaging and transportation are inconvenient, need to be installed and transported as a whole, and have no anti-freezing ability.
In summary, the three types of solar collectors have their own characteristics. The common type of solar collectors occupy most of the solar market with its low cost, long life and high efficiency. The heat transfer products have heat conduction effects. Mainly used in some high-speed heat transfer and heat dissipation industrial equipment, U-tube products are mainly used in high-end residential and water-demanding places with high water quality requirements.