Evacuated Tube
Evacuated Tube
Evacuated tubes are made up of two layers of borosilicate glass. Borosilicate glass is a strong glass that can withstand high internal pressure and external force. The outer tube is transparent allowing UV rays to pass through with minimal reflection. The inner tube is coated with a thermal radiation absorbing film, aluminum nitride (AlN). The film also reduces reflection in order to increase absorption. The two tubes are sealed at one end and the air in the gap between them is evacuated while the glass is heated thus creating a vacuum. This is achieved through a very delicate process.
The Vacuum Space
The reason for the vacuum space is because it forms a heat insulating barrier and once the radiation is absorbed through the evacuated tubes the heat that is generated will not escape into the atmosphere. This is similar to a flask or a double glazed window.
Evacuated Tube Layout
With the vacuum space in place the evacuated tubes can work well even in cold weather as apposed to flat plat collectors which have poor performance under cold weather conditions.
Heat Pipe
A heat pipe is situated within each evacuated tube engulfed by an aluminum heat fin. The tube is tightly sealed to prevent any water, dust or air from entering and affecting the performance of the heat pipe and the aluminum heat fin.
Heat Pipe
A heat pipe is an extremely efficient thermal conductor that transfers large quantities of heat via a thermal conducting fluid. A small amount of this fluid is sealed inside the heat pipe. Once the heat pipe is heated due to the absorbed solar energy the fluid inside it vaporizes and rises to the condensing zone where the heat is transferred to the water flowing through the manifold. The loss of heat causes the vapour to condense and flow back down the heat pipe where the process is once again repeated. The heat pipe is made of copper in order to maximize the heat transfer rate.
With this technology, heat is very efficiently transferred from the tube to the water. Heat pipes are widely used in many applications including air conditioning and computers as they provide reliable long-term performance.
Learn more about the evacuated tube solar collector.