The official SD chimney (power generator)

Factual Questions
1

I am truely impressed on how the hot-coffee-mug thread (“Hot” coffee cup) turned out debate-wise (like in the best of days of SD) … so here we go again … with a different topic to throw your engineering punches into:

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We all know the chimney effect (a tall, very long vertical tube, where air starts to flow up magically, thus possibly spinning a helice/impeller/propeller in the chimney, connected to a generator, hencely producing energy).

Say, I want to get into “free-energy-for-windstarved-remote -places w/ little sun” business to make more money than Bill Gates… help the ones in need, and serve my local community …

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What would be a good design for my electric chimney?

  • any thoughts on diameter vs height ratio?
  • is a cylinder optimal or would some kind of a flared cyl. be better (think: trumpet standing on floor - progressively smaller diameter = higher flowspeed?)
  • any ratio for air ingress on the lower side? … I assume you could choke the full effect with too small an air-ingress, but could you also oversupply air and stall performance?
  • optimal height? (probably: the higher the better, but also the-higher-the-more-static-problems → problems would be “runaway” with height)
  • how much energy could be harvested from an industrial sized chimney (say 3m across (ID) x 50 m tall)? … back of the envelope calc. is OK.
  • could there be any engineering features to increase its performance (vortex shaped inner tube, smaller diameter where you put the helice to get faster flow? …etc…)
  • would that really work 24/7/365.25??? (maintainance aside)

any thoughts?

I accept junior-partners for my endeavour: Ronald Wayne - Wikipedia :wink:

2

My first thought is that you’re a little late to the party. The earliest design I know of for generating (mechanical) power from a chimney was created by Leonardo Da Vinci. As far as I am aware though, he never actually built one. He just described one in his notes.

There are a lot of folks experimenting with the idea of solar power to heat the air that goes up the chimney. Wikipedia is probably a good place to start, though the Wikipedia article doesn’t have any engineering type data in it. But you can probably follow its links to get more technical data.

ETA: You also may need to be careful you don’t infringe on this patent, which still has a few years before it expires:

3

neither will I …

but there is good information here:

lots of small and not so small project, that had pretty much all in common - they all failed (but often for quite trivial reasons)

4

step aside!

here comes my shiny simulation of the chimney …

a couple of surprises:

  • chimney height is not too relevant
  • chimney diameter is more relevmant (but again, less than I’d thought (friction on the sidewalls))
  • outside temp. is pretty irrelevant, too … so the system works pretty much the same at 15C as 30C
  • the main performance driver is the surface of the umbrella, the stack sits on and which prewarms the air?..
5

I’m reminded of an article that (with googling) turns out to be Defeating the Son of Andrew by Leon O. Billig from the February 1994 Analog. He proposed lining the southeast coast of the US with giant solar towers to sap the energy out of approaching hurricanes. And as a secondary effect provide water and hydroelectricity. I haven’t tracked down a version of the article online.

6

I remember reading some article that mentioned this effect was used in architecture in the Midlle East for many centuries to create air flow in buildings, since it was before air conditioning…

7

yes, solar cooling …

you suck in air and channel the flow below ground in pipelines, where the air is cooled down and replaces the warm/hot air within the building while streaming up…

here’s a good synthesis: