Heat pipe vacuum tube

Vacuum tube technology adopts building architecture that greatly limits heat loss and enhances the capacity to capture solar radiation. This results in increased thermal energy storage in adverse environmental conditions with significantly higher overall efficiency. The use of vacuum tubes allows a substantial simplification from the manufacturing point of view by eliminating many structural components that are sources of heat loss.

By concentrating in one element the main functions for capturing solar radiation and transmitting the same to elements for transporting heat, better thermal efficiency is obtained; it also improves the mechanical strength, because less surface is subjected to wind forces. The tubular shape, with respect to the flat one, ensures that the sun affects the surface of the tube almost always at right angles, thus minimizing losses due to reflection and maximizing the amount of heat absorbed.

Each vacuum tube consists of two coaxial glass tubes; The outer tube is transparent borosilicate glass, which is extremely resistant, while the inner tube, also made of borosilicate glass, is coated with a special selective coating (AI-NAI) with excellent absorption properties and low emission in the infrared spectrum. In the hollow space between the two tubes, the air is removed to form a vacuum that produces a thermos effect, eliminating heat loss to the outside even at low temperatures.

The heat pipe is found between them; a typical heat pipe is a tube (hollow cylinder) of closed copper, containing a small amount of liquid with a low boiling point; the rest of the tube is filled with the liquid’s vapour, so that there are no other gases. A heat pipe is used to transfer heat from one end of the pipe (hot) to the other (cold), through evaporation and condensation of the coolant. The hot end, in contact with a heat source, releases heat to the liquid coolant, which vaporizes and therefore increases the vapour pressure in the tube. In addition, the latent heat of vaporization absorbed by the liquid decreases the temperature at the hot end of the cylinder; the vapour pressure near the hot end is higher than the balance at the cold end. This difference in pressure causes a very fast transfer of steam towards the cold end, where the excess vapour with respect to the balance condenses, giving off heat at the cold end. An interesting property of heat pipes is the temperature at which they are efficient: in a pipe in which a vacuum has been created and a very small amount of water has been inserted, the boiling temperature approaches 0°C. For this the heat transfer will begin when the hot end is at a temperature just slightly higher than the cold end. For the same reason, a heat pipe containing water will work at temperatures above 100°C, because the increase of the pressure inside proportionally raises the boiling temperature of the water contained.

Nearly all the energy is transferred quickly to the cold end when the fluid condenses, creating a very efficient heat transfer system with no moving parts. Last but not least, heat pipes contain no moving parts and therefore do not require maintenance.