The solar tower with depression: scientific and technical aspects by François MAUGIS, Energy Environment Association. (from the evidence provided by the SUMATEL company)
The operating principle of the French professor's vacuum tower Edgard Nazare which he had baptized “vortex tower” or “aerothermal power station” (to be compared to the “Atmospheric Vortex Engine” of the Canadian engineer Louis MICHAUD), can be approached from two different angles: the “thermodynamic” approach or the “fluid mechanics” approach.
1.1. The thermodynamic approach (Carnot principle)
We start from the fact that the temperature difference between the upper and lower layers of the atmosphere, induces a cycle efficiency (a few%) which is applied to a quantity of heat evacuated by the tower as a function of its size and of the speed. rising air. Overall, this gives the recoverable mechanical power. Of course, series of parameters modify these calculations, but the guideline is there. NAZARE therefore concludes by saying that if the Archimedean equilibrium is at a given altitude, there is a state temperature.
The difference between the air temperature at ground level (at the entrance to the tower) and the air temperature at altitude, at the equilibrium level (at the top of the swirling phenomenon) therefore constitutes the Carnot cycle. .
1.2. The "fluid mechanics" approach (Bernoulli's equation)
We start from the fact that the atmosphere from the ground has a state curve (temperature and humidity) which induces or not a convective cell (cloud). The tower is only present to transform the convective cell into a vortex phenomenon. In nature, this vortex can only be established under specific conditions. If these precise conditions are not met, we only have disorderly “convective bubbles”. It is the Bernoulli equation associated with the calculations of "pressure drop and boundary layers" which gives the mechanical power of the system as a function of the state curve of the atmosphere.
1.3. Results of these two approaches
The SUMATEL company (evoked in this document) worked with Professor NAZARE on the “Carnot” approach for years. She then worked on the “fluid mechanics” approach with the state curve of the atmosphere. In both cases it obtained very similar mechanical power results. By confirming the reality of the first hypotheses, this consistency of results has reinforced the SUMATEL company in the pursuit of the project and of research and development efforts.
Prototype of Vortex solar tower made by Sumatel
2. Operating mode
It is the temperature difference between the air at altitude (top of the atmospheric snorkel) and the air at the base of the tower that operates the system. It is not, as has sometimes been mistakenly said, the temperature difference between the base and the top of the actual tower.
The vortex tower exploits "a natural thermal bubble" and therefore the difference between the density of the air entering at the base of the tower and the density of the air at the top of the snorkel. The rotation of this mass of air makes it possible to constitute a "fictitious" chimney (the tuba or column of rotating air) of height much greater than that of the tower (real chimney), which isolates the phenomenon from the law. “Altitude-pressure-temperature” and therefore induces an equilibrium altitude.
The power of the tower (mechanics of Bernoulli fludies) depends only on the product: "density difference per height of the tuba".
It is the temperature difference between the air on the ground and the air at the top of the snorkel that determines the rate of rise of the air.
The calculations of NAZARE, those of SUMATEL, as well as those entrusted to "XJunior" and "Mathematics Partner", confirm that the general rules mentioned above are respected. The vortex tower works like a natural atmospheric phenomenon and follows the same rules and the same mathematical laws as those applied to these phenomena.
To date, here is what has been demonstrated:
- the phenomenon can start alone or artificially
- the phenomenon can be self-sustaining
- the phenomenon goes up in the atmosphere
- the direction of rotation does not matter (almost zero Coriolis)
- A large air mass allows the stability and power of the phenomenon and the height of the snorkel
- Only the state curve of the atmosphere (temperature-humidity) and the adiabatic and pseudo-adiabatic curves regulate the phenomenon.
- The phenomenon produces a significant mechanical power of which only part can be exploited (under pain of suffocation)
- the phenomenon produces condensation water in the tower, but in small quantities (two-phase flow)
- the phenomenon produces cold in large quantities (less than 0 ° C in the vortex inside the tower)
- the phenomenon creates altitude clouds (function of the state curve of the atmosphere) and, under certain conditions, rain
The evolutions compared to the initial project of Professor Nazare
The observations indicated above led SUMATEL to modify the geometry of the tower by modifying the ratio between the two air passage sections (at the base of the tower and at the venturi neck).
For Nazare, we had to have an air intake section ten times larger than the section of the venturi neck, SUMATEL brought this ratio back to 7.
For a tower of 300m that would be the size of a first operational and truly demonstrative prototype, the air flow would be 130 tons / second for a delta of temperature (temperature difference between the air intake at the base of the tower and top of the swirling phenomenon) of 30 ° C and a moisture content of 85%. In this case, the exploitable mechanical power would be 250MW, the air velocity would be 4m / s at the entry of the tower at ground level, and 200 m / s (note: more than 700 km / h !!) at the venturi pass (diameter 50 m instead of 30 calculated by Nazare) for an inertia of 100 t / s.
Given the size of these towers and atmospheric disturbances generated locally (cloud, rain or drizzle, cooling the air on 2 3 km around the tower) it goes without saying, as Nazare said, that they will be located far from built-up areas and, of course, in hot regions.
- Information about SUMATEL's work
- Download reports and files on solar towers
- Contact details of the Energy Environment Association:
Association Energy Environment
7 Fontaine Chaalis road