About Evacuated Collector Tube

The evacuated tube is the key component to all the thermal heaters and systems. It’s similar to a conventional Dewar flask and consists of two borosilicate glass tubes, resistant to high chemical and thermal shock. The outer side of the inner tube is coated with a sputtered solar selective surface. This coated inner tube is closed at one end and sealed at the other end to the outer tube. The annular space between the outer tube and inner tube is evacuated to avoid heat loss in conduction and convection.

The key element determines that the function of tube is the technology of the film coating, and Gaia Solar uses the Patent of the University of Sydney to produce tubes and our tube is the best efficient tube you can find in China, with the highest absorption rate of near 97% compared with common rate of 94% and lowest emission rate near 3% compared with common rate of 5%. At this efficiency, it has been very hard to improve the function any more, even very little extent. And the film can be divided into bellowed four layers:

The four layers are metal infrared reflector layer, HMVF cermet, LMVF cermet and anti reflection layer. When the tube is placed into the coating machine, pumps draw the air outside and form a vacuum at about 1x10-3. Later, some nitrogen is sent into the coating machine and form a film of Al/N-Al. At this stage, the main percentage of the film is AL since there is only very few Nitrogen entering the coating machine. So this stage film is called High Metal Value Film (HMVF). And little by little, more and more nitrogen is released into the coating machine, and form Al/N-AL film, but at the stage, the percentage of Nitrogen increases and forms Low Metal Value Film (LMVF). At last, an anti-reflection layer is made on tube to reduce the emission rate of the film. Thus the coating procession is finished.

During the whole process, with continuous inputting of nitrogen, films with different content of AL/N-AL form. Some companies thus said their tubes have many layers and even ten thousands layers. But it is not the number of layers and the thickness of layers that affect the efficiency of the tubes, the production technology, design and even the quality of the materials make the final difference.

Bellow is the efficiency curve of Gaia Solar vacuum tube and technical datasheet on tubes. .