This is actually a difficult engineering question. The superiority of a hyperboloidal shell over conical or cylindrical isn’t clear cut, especially over a conical shell. But the chief difference is that at all surface points of both the cone and the cylinder have at least one principal curvature of zero, meaning that both can be “rolled out flat”, or formed from a sheet of paper. The hyperboloid cannot be, so it resists local deformations everywhere on its surface, and hence it’s “stiffer”. Technically speaking, a hyperboloidal has a negative Gaussian curvature everywhere, while the other two have 0 Gaussian curvature everywhere.

A real hyperboloidal cooling tower is actually a compromise, because air accelerates as it rises inside the tower, and the cross section has to be reduced with height for efficient non-turbulent flow. Yet, a slight flaring at the top is found to be more efficient for dispersal of warm air. So, hyperboloidal cooling towers are generally wider at the bottom than at the top, and bottom part closely approximates a conical surface.

What the public isn’t generally aware of is that hyperboloidal cooling towers are mostly empty space. All the cooling coils and surfaces are located at the bottom of the tower. The tower itself is designed to maximize air draft that would naturally occur with air rising after contact with heated surfaces. Via Yahoo

Nice article, however it’s “towers” and definitely not “tower’s”

Is apostrophe placement _really_ so difficult, or have we gone back to pre-Johnsonian times, when you could use grammar and spell any way you liked?

We consider ourselves admonished. Title updated.

Now that you have sorted out your punctuation, you might consider another amendment. The shape of the cooling towers is actually called a hyperboloid.

As you might expect, Wikipedia has an article which can be found below:

Hyperboloid:

A hyperboloid is a 3 dimensional solid or surface that is formed by rotating a hyperbola through 360 degrees. The title asks why a cooling tower is hyperbolic in section. This is correct, as a section through a cooling tower, would be 2 dimensional and hyperbolic in shape. However, I actually thought that cooling towers were formed from a catenoid so as to have a minimal surface of revolution. If you get a handful of dried spaghetti and twist it so that the top and bottom have larger diameters than the middle you should achieve this shape which is made entirely from straight lines. A circle, ellipse, hyperbola and parabola are all conic sections; I don’t believe that a catenoid can be formed from any section through a cone?

I don’t know if it’s my imagination but in the photo above the bottom third of the cooling tower looks to be linear (a straight line). Surely that can’t be possible if it’s a curve, hyperbolic or not?

The Wikipedia entry re Hyperboloids shows this quite well, I think. When you look at the photo of the wireframe model, the structure suggests that this point will be approaching a straight line.

They are called, ‘asymptotes’, which are straight lines that a curve tends to but never reaches.

Thank you Fred and Phil. All seems pretty clear know.