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 and is implemented because a vacuum space is a good heat insulator and once the radiation is absorbed through the evacuated tubes the heat that is generated will not escape into the atmosphere.
Creating a vacuum space between the glass layers is an efficient method to absorb solar radiation, converting it into heat and preventing the heat from dissipating. This method also assures that the outside layer of the evacuated tubes does not heat and thus does not cause any harm to occur if the tube was to be touched.
With the vacuum layer 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 an evacuated tube. The evacuated tube is tightly sealed to prevent any water, dust or air from entering and affecting the performance of the heat pipe.
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 where it vaporizes and condenses to transfer heat. Usually aluminum or copper heat pipes are used in order to maximize the heat transfer rate.
The condensing zone is inserted into a copper manifold where the heat from the heat pipe is transferred into the water passing through the manifold. A manifold is a copper pipe with a set of sleeves distributed along its length. Each sleeve receives the condensing end of a heat pipe. At this intersection the water flowing through the manifold absorbs all the heat from the condenser and continues along the manifold.
Manifold
Once the heat pipe is heated the thermal conducting 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 vapor to condense and flow back down the heat pipe where the process is once again repeated.
With this technology, heat is very efficiently transferred from the heat pipe to the water. Heat pipes are widely used in many applications including air conditioning and computers as they provide reliable long-term performance.