Vacuum tube technology is currently one of the most effective in terms of solar thermal collectors, the qualities of this useful element allow optimal energy absorption, so let’s dig a little deeper into them.
Although for a long time the system based on vacuum tubes was quite expensive and difficult to access, today it is already present in a considerable number of equipment and devices such as solar thermosyphons or solar water heaters, ideal for obtaining hot water. sanitary from solar thermal energy, and they have invaded the market.
First of all, to understand the reason for the effectiveness of this vacuum tube technology, it is necessary to know the process in which heat energy passes from one body to another, and where a greater or lesser optimization of a collector is determined with respect to to another.
Let’s learn to identify the 3 forms of heat transmission from one body to another.
1 – Driving:
It is the transmission of heat that occurs between two bodies at different temperatures and that are in permanent direct physical contact or it could be two areas of the same body, also at different temperatures. The flow of heat transmission will largely depend on the size of the contact surface between the two areas of different temperatures and the thermal instability that exists between them. Here we can check this transmission by coming into contact with the hot body or simply by holding a metallic element that at the other end is subjected to fire.
2 – Convection:
It is a heat transfer between fluids and not between solids. This occurs because when the temperature of a fluid rises, it loses density and rises over the coldest and densest channel, transferring all its heat to the latter. We can check its operation by touching the radiator or stove and we will notice a slight current of warm air that is rising.
3 – Radiation:
Here it is not necessary for the bodies to be in contact to transmit heat, in fact sometimes there may be voids between them. Let us remember that every body, due to being at a temperature higher than absolute zero, emits thermal electromagnetic radiation and the higher the temperature, the broader the radiation it emits. This transmission can be easily verified by being near a stove or some very hot object, and we will easily notice the radiation that it gives off. If we get too close to the hot object, what we will notice the most is the heat transfer by convection.
In the case of solar thermal energy collectors, their operation occurs from the incidence of the sun on the collector so that it rises in temperature, which seeks to heat a certain fluid, which is generally water. Hence the importance of having very efficient collectors in capturing energy.
It is at this point where the importance of good vacuum tubes lies, which allow us not only to make a correct conversion of solar radiation into heat, but also to reduce the losses by conduction and convection that the collector has by the simple fact of being in contact with the outside environment. In vacuum tubes, conduction and convection losses are eliminated because, as its name indicates, a vacuum is created between the two concentric tubes that make up the tube, and the vacuum only allows the transmission of heat by radiation.