|
|
Solar ABC
Vacuum tube
|
Vacuum tubes are the heat absorber of the solar water heater. They absorb solar energy converting it into heat for use in water heating. Sunpeak most using vacuum tube is the "twin-glass tube". This type of tube is chosen for its high reliability, good performance and low manufacturing cost.
|
|
Each vacuum tube consists of two glass tubes made from extremely strong borosilicate glass. The outer tube is transparent allowing light rays pass through with minimal reflection. The inner tube is coated with a special selective coating (Al-N/Al or ALN/AIN-SS/CU) which features with excellent solar radiation absorption and minimal reflection properties. The room between two layers of tube is evacuated to form vacuum, which is an important factor in the performance of the vacuum tubes.
|
|
In order to maintain the vacuum between the two glass layers, a barium getter is used. During manufacture the bottom of the evacuated tube is coated with a pure layer of barium. This barium layer actively absorbs any CO, CO2, N2, O2, H2O and H2 out-gassed from the evacuated tube during storage and operation, thus helping to maintain the vacuum. The barium layer also provides a clear visual indicator of the vacuum status. The silver colored barium layer will turn white if the vacuum is ever lost. This makes it easy to determine whether or not a tube is in good condition. See picture below. |
 |
 |
 |
 |
|
