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I asked in this question if there was a heat powered fan for residential steam rads, to increase air flow over them since natural flow is pretty weak.

Alas, looks like some wood stoves can use such a device, but in the $300 range and they are pretty bulky.

Looking at parts, I found some cheaper ($40 US) Seebeck effect generators (Reverse of Peltier effect) and I am wondering if I can build one myself that is worthwhile.

Found a Seebeck generator here that looks to be about the right size, attach to my rad right where the steam comes in, stick a computer style heat sink on the back (bum one from work), and then run the power into a small fan.

Now to find a small fan I can fit under the rad, and needs low DC power.

I am tempted to experiment, since for $40 this should be simple enough.

I know my rad is not hot enough at 100C max, but I wonder if I can get enough power out to run a small battery powered fan styled motor...

Am I going to fail? Or is there a chance this might succeed?

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How much circulation are you expecting out of a 5V fan? –  Tester101 Jan 16 '12 at 21:34
    
@Tester101 Not a whole heck of a lot. Basically anything better than natural airflow due to convection is a win. So whatever I can get out of it. The natural airflow is just barely enough to make the toilet paper (from the roll in our washroom) flutter or lift one square. –  geoffc Jan 16 '12 at 22:18
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I have a feeling their data sheet is optimistic, but let's go with that.

I've got right here a computer fan, moving a stream of air which is miniscule compared to most home radiators I've ever seen. It is consuming 1.6W of power to accomplish this feat.

Let's say you're already actually doing a really good job of moving air away from this radiator, and so its immediate environment is 25C. You stick a giant whopping block of copper on the back side of this generator, and end up with just a 5C rise over ambient on the cool side of the generator. (After, of course, coming up with a very thermally conductive connection between your round pipe and this flat object.) The chart says you need your steam pipe to be about 150C to get 1.6W out.

As I understand it, steam in homes isn't that hot. So you're not going to get the power you want, even under the above generous assumptions. And I don't think the air circulation you'll get from 1.6W of fan would even be worth it.

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Thanks! I appreciate the answer. Steam pipe should be closer to 100C probably at most. But I do have a clean flat square surface to mount it on. I think even a computer fans output would make a big difference. Be nicer to get more, but for $40 I am tempted to experiment still... –  geoffc Jan 17 '12 at 1:56
    
You might want to, instead of taking a random DC fan, hit up DigiKey, and use their fancy search to try and find the highest CFM fan which consumes less power than the data sheet predicts your seebeck generator will produce in these circumstances. No sense fiddling around with heat transfer systems when you're wasting your collected energy on an inefficient fan. Not sure how the generator will interact with a BLDC fan, but stuffing a big electrolytic cap between the two almost certainly can't hurt. If the fan doesn't want to start, or stutters, definitely try a cap. –  Jay Kominek Jan 17 '12 at 4:01
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