Solar Evacuated Glass Tube
Descriptions of Solar Evacuated Glass Tube
A evacuated tube or vacuum tube, known as a main component of evacuated tube solar collector, is mainly made of double-walled glass, namely inner tube, outer tube.
Two glass tubes are closed on one side and sealed with each other on the other side so that an evacuated space is formed.
The inner tube is coated with aluminium nitrite, a special selective material, which serves to absorb radiation falling on it.
To maintain the vacuum between the two glass tubes during manufacture, a barium getter (see below) is used at the bottom of the glass tube. High temperature produced during manufacture will cause tube bottom to be coated with a barium layer, which provides a visual indicator of the vacuum status. The silver coloured barium layer will turn white if the vacuum is lost. Based upon this, we can easily determine whether or not a tube is operating correctly. See right picture below.
Model | Glass vacuum tubes |
Glass Material | High-quality borosilicate glass 33 |
Thermal Expansion | 3.3x10-6 ℃ |
Glass Tube Diameter | ¢47mm / 58mm |
Inner Glass tube diameter | 37mm / 47mm |
Thickness of Vacuum | ¢5mm |
Length | 1500mm ,1800 mm |
Glass Wall thickness | 1.6 mm / 1.8mm |
Single Tube weight | 1.35kg ; 2.0kg |
High Vacuum, long-term stability | 5×10-3 Pa |
Absorber Material | Aluminum |
Absorptive Coating | Aluminum Nitride |
Absorption Coefficient | α 0.90-0.93 |
Wind Resistance | 30m/s |
Emittance | <8% (80℃) |
Heat Loss | <0.8W/ ( m2℃ ) |
Maximum Strength | 0.8MPa |
Freezing Tolerance | -30 ℃ |
Hail Resistance | ¢ 30mm hail |
Insolation Temperature | 250 ℃ |
Start-up Temperature | ≤25 ℃ |
Life Time (years) | 15 years |