You may have seen these, around the world or in some film or TV series huge objects built near one thermoelectric or nuclear power plant. To give an example, the iconic structures present near the Springfield nuclear power plant in the world of the Simpsons are very famous. These objects are called cooling towers and the reason why these structures have this strange hyperboloid shape, in these specific application cases, is not to be found in architectural intentions, but rather in technical features which guarantee aoptimization of the cooling process and of quantity of material with which they are built.
What are cooling towers and how do they work
Also calls evaporative towerscooling towers are real heat exchangers. A heat exchanger is a system in which one occurs exchange of thermal energy from a fluid at high temperatures with other fluids at lower temperatures. In the specific case, the high temperature fluid that you want to cool is waterfallwhich undergoes a heating process upstream due to the heat production of the machinery used in the power plants. To be reintroduced into the cycle and ensure new dissipation of heat produced by the machinery, the water must be re-introduced cooled. This is where the need for this system arises, although the use of this type of tower is required when dealing with large volumes of water in play.
In a very simplified way, inside this large tower structure we find a water distribution system (at high temperatures) which maximizes the heat exchange surface of the volume of water distributed. Falling by gravity, the generic drop of water exchanges heat with the surface it is in contact with and accumulates at the bottom at a lower temperature. The heat exchange also happens with theair present inside the structure: from the bottom (which is open to the environment) the air present in the atmosphere enters and increases its temperature, moving naturally upwards. In this phase heat exchange, therefore, can be generated water vaporwith the visible result of the release of fumes, which are none other than the vapor produced by this energy transfer.
Optimization through geometry
To ensure this cooling process, you need to large heat exchange surfaceswhich is why these towers always have significant diameters in plan. Furthermore, to make the most of the convection process, it is also necessary to have important heights. To obtain an efficient system of these important dimensions, therefore, we resort to this particular construction form, called single-layered hyperboloidor even hyperbolic hyperboloid.
The advantage on air movement
Thanks to the shape obtained through this well-known geometric figure, the cooling tower has a series of advantages. First of all, the possibility of confiscating large quantities of incoming airin the lower area. Furthermore, the narrowing in the central area allows for speed up the outgoing air flow which naturally moves upwards having reduced its density.
The advantages from a structural point of view
While optimizing air movement is important, the real benefit associated with using this shape is structural type. In fact, given the geometric constraint on the heights and diameters involved, a structure of this type becomes daring to achievealso in terms of costs. Suffice it to say that you can reach heights of up to 200m. However, the particular shape of the structure allows it to be optimized thickness of the tower. Indeed, unlike for example a simple cylindera one-sheet hyperboloid has a distribution of internal forces due to their own weight which are always compressive. Since weight is an important stress component in this type of structure, this result guarantees the construction of towers reinforced concreteof reduced thickness with limited quantities of steel reinforcement. One could compare the structural optimization obtained through this shape with that guaranteed by the thickness of the egg shell, obviously with the necessary proportions between the two structures!
