Vacuum Tube

About Vacuum Tube

How it works?

Glass heat pipe evacuated tube also consists of a two layers of glass with a vacuum in between the layers like conventional solar vacuum tubes. On the other hand, its difference from conventional vacuum tubes is that the open end of the tube is closed using a special geometry like a dome shape to increase resistant to axial loads in pressurized reservoir systems. This enclosed area, which is inside the inner tube, is vacuumed and a heat transfer fluid is injected into it. The special selective coating on the outer surface of the inner tube changes solar radiation into heat then absorbed solar radiation is transferred to a heat transfer fluid within the tube. This liquid quickly heats up, changes its form to gas and rises to the top. It reaches the dome shaped condenser in the usage water reservoir. Since the outer surface of the condenser is in contact with the relatively colder usage water in the reservoir, the heat transfer fluid in the form of gas condenses on the inner surface of the condenser. The condensing chemical returns back in droplets to the sun-exposed base of the tube. As long as the system is heated by the sun, the circulation continues.


Contrary to conventional vacuum tubes, there is no water circulation inside the tube, so calcification problem due to water is prevented. Due to no water circulation, there is no risk of freezing or breaking the tube in winter.

Property Value & Unit
Length 1930 mm
Outer tube diameter 47 mm
Inner tube diameter 37 mm
Glass Thickness 1.6 mm
Thermal expansion 3.3x10-6 oC-1
Material Borosilicate glass 3.3 
Surface coating material AL-N\AL selective
Light absorption rate 90% Avarage 40 kcal/h
Emission rate 4-5 %
Vacuum P<0.005 Pa
Empty tube temperature >200oC
Heat loss coefficient <0.8 W/m2 .K 
Reflection ratio 7 % (100 oC )