The Glass tubes are a major component in such systems. Every single evacuated tube has two glass tubes. The tube on the outside is made of extremely strong and transparent borosilicate glass. This tube can withstand impact of up to 25mm hail stones. Now That’s truly durable!
The Inner tube is also made from borosilicate glass and is given a special coating which exhibits excellent properties of sunlight absorption and minimal heat reflection properties. Air is removed from the space between the two glass tubes thereby creating vacuum between them. This Vacuum acts like an insulator and also helps in reducing the radiant heat losses.
What happens inside?
Inside the evacuated glass tube a copper heat pipe is installed. This heat pipe acts as a medium of heat transfer to its tip. This tip is connected to the collector’s heat exchange system. As water passes through this heat gets transferred to the water. The Heat transfer system is securely insulated in an aluminum enclosure.
How does the Heat get transferred to the water?
The arrangement for heat transfer is rather simple. The copper heat pipe is hollow and is filled with acetone. The hollow centre of the heat pipe is vacuum and hence even at temperatures as low as 40°C the acetone vaporizes (i.e. it boils). This vapor then rises to the tip of the heat pipe where the heat is transferred to the water in the heat exchange system.
Now as the heat transfer process continues the vaporized acetone condenses and simply flows back down the heat pipe and the process keeps on repeating.
The process of heat transfer is more efficient to that of conventional flat-plate collectors and solid copper rods. Thus heat transfer takes place more effectively from the evacuated glass tube to water.
Now that you know the benefits of an evacuated tube collector, you may decide to buy your own. Go for It!