Air circulating fan- no energy cost Solved

[iann]

You can buy solar powered fans, which would be the best solution for obvious reasons, but they aren't cheap (at the power levels you need) and they aren't the sort of thing that's easy to cobble together from stuff you find in the attic

[Ernie]

Chris. The size of the fan blade and the prop to drive it will be determined by experiment. The real key to achieving efficiency is the spindle/ bearings friction losses.

The cost of an electric fan and the power it consumes are I agree not really significant; I just want to see if I can achieve the same result using no power other than what he upstairs provides for us!

I had some success with a similar idea. Used a biycle dynamo fitted with a wind driven prop to drive it, free illumination in my workshop.That did not last long due to the variable amount of power it generated.

Hey one day we may all have to turn the clock back 100 yards and come up with energy producing gadgets !

[iann]

Surely ultimate efficiency is not necessary? You just make the outside rotors larger than the inside fan so that it rotates. Although obviously you don't want a giant windmill grinding away at a rusty spindle! Seems like you want want it geared up significantly to move the internal air even with a gentle breeze, but the gearing would certainly lead to losses. If you use a bicycle chain for your power transmission, you could pick from any one of 18 different fan speeds

[Ernie]

Perhaps I did not make it clear when I mentioned efficiency- I was referring to the ability of the external fan to turn the spindle even in a very light breeze. Any reduction in friction will help. As for gearboxes I have at least a dozen precision gearboxes used in my fast model boats. Friction losses in these is very small.
Having an engineers lathe in my workshop makes things easy for me.I can always make what I dont have to hand.

It may not work but the fun is in the trying!

[tony_lb]

Years ago I worked in a school chemistry lab that had a fume cupboard with an extractor that had no actual fan at all. Two wide pipes making a T, with a slight funnel on one, and the air was pulled through from the fume cupboard whenever there was a breeze. Might be something worth thinking about. Same principle as the one that keeps planes in the air.

They weren't trying to be environmentally sound, the local electric supply was unreliable.

Tony

[Phil_SK]

Like a simple aspirator pump?

[iann]

My aspirations are still for ventilation that works harder on hot still days

[Julie]

Ernie, I would like to see photos of your gadgetry when complete!

Btw, eccentrics are needed.. society would never advance otherwise.

[Hob]

Julie Wrote:
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> Btw, eccentrics are needed.. society would never
> advance otherwise.

some consider me eccentric .............others just think i'm mad as a hatter

[tony_lb]

Phil_SK Wrote:
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> Like a simple aspirator pump?

It was based on Bernoulli's Principle. The inlet (as far as I can recall) narrowed down to increase air speed, which dropped the pressure in the pipe which met it just in front so air flowed up the joining pipe. Same idea as in a perfume spray which just uses an air bulb.

Mind you, initially they built it back to front and it blew air in instead, blowing fumes into the lab!

Tony