Vacuum tubes assimilate the advanced 12 layers of spattering deposition of trivalent elements, high borosilicate glass, gradual change of SS-AL/CU selective complex absorptive coating and these make vacuum tubes have high performance of absorptance and low reflection ratio. Through the interlayer, vacuum has a unique effect of thermo, with its temperature up to 380 degrees of idle sunning, performing a strong heating function. Evacuated tubes are the absorber of the solar water heater. They absorb solar energy converting it into heat for use in water heating. Evacuated tubes have already been used for years in Germany, Canada, China and the UK. There are several types of evacuated tubes in use in the solar industry.
Our tubes are the “twin-glass” tube. This type of tube is chosen for its reliability, performance and low manufacturing cost. Each evacuated tube consists of two glass tubes made from extremely strong borosilicate glass. The outer tube is transparent allowing light rays to pass through with minimal reflection. The inner tube is coated with a special selective coating (AL-N-AL or AL-N-CU) which features excellent solar radiation absorption and minimal reflection properties. The top of the two tubes are fused together and the air contained in the space between the two layers of glass is pumped out while exposing the tube to high temperatures. This “evacuation” of the glasses forms a vacuum, which is an important factor in the performance of the evacuated tubes.
Why a vacuum? As you would know if you have used a glass lined thermos flask, a vacuum is an excellent insulator. This is important because once the evacuated tube absorbs the radiation from the sun and converts it to heat, we don’t want to lose it!! The vacuum helps to achieve this. The insulation properties are so good that while the inside of the tube may be 150℃/304℉, the outer tube is cold to touch. This means that evacuated tube water heaters can perform well even in cold weather.
