Why are the cooling towers on nuclear power plants funny shaped?

It's partially due to engineering practicalities too.<p>Take two rings (imagining they are the top and bottom of the tower) and tie string vertically between them at 20 or so different points (these are the long girders used to build the tower). You now have a straight cylinder.<p>Twist the top ring slightly, and all the 'girders' remain straight, but the cylinder becomes a squashed hourglass, just like a cooling tower. This shape is a lot stronger, but still uses plain straight girders.

I once went on a tour through a nuclear power plant and the cooling tower was the one place where you could really get an idea of how much energy is being produced there. You could feel the draft about 100m away and once you were inside it was overpowering.<p>I mean we saw the turbines, power transformes the spent fuel pool and the reactor hull and everything. But there you did not really get the right impression, as opposed to standing inside a tower which produces clouds which you can see from more than 50km away.

tl;dr: It is called a hyperboloid shape and is very strong compared to other curved surfaces because it can be built or supported by straight beams. <a href="http://en.wikipedia.org/wiki/Hyperboloid_structure" rel="nofollow">http://en.wikipedia.org/wiki/Hyperboloid_structure</a>

I used to work at the stations mentioned, we had big signs on the nearby highway pointing out that the "smoke" coming out of the towers was just water vapour. The actual pollution was generally pretty hard to spot thanks to various ash and particulate collection methods in action, that is unless one of the boilers was being restarted and diesel was being burnt, in which case the smoke was quite black and visible.

OT: the div#dd_ajax_float element (the share buttons) on that page is really annoying. Its fixed location and its style (e.g. it has a drop shadow, making it seem to be physically closer than the content) make it seem 10x more important than the content itself. I have to set it to display:none to read the page.

Minor point of clarification: the article says "pure steam...has no ceiling temperature." Water vapor begins to decompose into oxygen and hydrogen around 2200C(1). Probably well above the threshold of anything capable of generating electricity, but it does have a ceiling.<p><a href="http://en.wikipedia.org/wiki/Water_splitting#Thermal_decomposition_of_water" rel="nofollow">http://en.wikipedia.org/wiki/Water_splitting#Thermal_decompo...</a>

The BBC documentary linked at the end of this article, "Fred Dibnah, Steeplejack", is right up the alley of many here on HN: <a href="http://www.youtube.com/watch?v=xuSW9kOBADo" rel="nofollow">http://www.youtube.com/watch?v=xuSW9kOBADo</a>

I always thought they were built that way to cool the air faster due to the Jules-Thomson effect.

Upvoted for the hidden Wacky Waving Inflatable Arm-Flailing Tubeman link.