Construction of all-glass vacuum tubes:
The structure of all glass vacuum tube consists of inner glass tube, solar selective absorption coating, vacuum sandwich, cover glass tube, support (spring clip), getter and so on.
1. Inner glass tubes are used as flow pipes for water.
2. Solar selective absorbing coatings such as copper oxide, black nickel, black chromium, black zinc and black copper are uniformly coated on the outer surface of inner glass tubes by vacuum deposition, sputtering and electrochemical treatment to absorb solar radiation energy.
3. The inner glass tube coated with selective coating is sealed in the cover glass, and then vacuum is pumped between the inner and outer glass tubes to form a vacuum sandwich with a vacuum of 0.05 Pa to reduce the heat loss caused by air convection and conduction, which is similar to the principle of hot water bottles.
4. All-glass vacuum collector tubes are designed with single-ended opening and sealed by annular melting of inner and outer tubes at one end. The other end of the inner tube is a closed hemispherical round head. The spring clip is used to support the round head on the inner end of the cover glass tube, so that when the inner glass tube absorbs solar radiation and the temperature rises, the glass round head forms a free end of thermal expansion, thus buffering the water heater working. The thermal stress at the end of the opening of the vacuum collector tube is induced.
5. After the vacuum tube is heated, the trace gases (mainly water vapor) originally adsorbed on the tube wall will be released, affecting the vacuum. The getter and the getter film are used to absorb the released gases to maintain the high vacuum in the collector tube.