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Heat powered stove fan
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Nick



Joined: 02 Nov 2004
Posts: 33762
Location: Hereford
PostPosted: Wed Jan 31, 18 9:31 am    Post subject:  Reply with quote    

Hairyloon wrote:
Nick wrote:
Yeah. I’ll recheck the figures next time it’s on.

Don't go to any much trouble: the critical temperature would be the top of the stand, which would be all but impossible to measure.
Probably just a bit too hot for the 150°C cells...


I’ve a laser pointer thermometer. It’s easy to measure with that. As long as it’s below about 600C it’s pretty accurate.

Hairyloon



Joined: 20 Nov 2008
Posts: 14871
Location: Today I are mostly being in Yorkshire.
PostPosted: Wed Jan 31, 18 10:16 am    Post subject: Reply with quote    

Nick wrote:
Hairyloon wrote:
Nick wrote:
Yeah. I’ll recheck the figures next time it’s on.

Don't go to any much trouble: the critical temperature would be the top of the stand, which would be all but impossible to measure.
Probably just a bit too hot for the 150°C cells...


I’ve a laser pointer thermometer. It’s easy to measure with that. As long as it’s below about 600C it’s pretty accurate.

Well if you're going to be like that about it, can you do me a thermal image of a fan in operation?

Slim



Joined: 05 Mar 2006
Posts: 4922
Location: New England (In the US of A)
PostPosted: Wed Jan 31, 18 12:48 pm    Post subject: Reply with quote    

I thought those fans used Stirling engines?

Edit: nevermind, quick google showed that most are thermoelectric but there are stirling engine options

Nick



Joined: 02 Nov 2004
Posts: 33762
Location: Hereford
PostPosted: Thu Feb 01, 18 6:37 pm    Post subject: Reply with quote    

Hairyloon wrote:
Nick wrote:
Hairyloon wrote:
Nick wrote:
Yeah. I’ll recheck the figures next time it’s on.

Don't go to any much trouble: the critical temperature would be the top of the stand, which would be all but impossible to measure.
Probably just a bit too hot for the 150°C cells...


I’ve a laser pointer thermometer. It’s easy to measure with that. As long as it’s below about 600C it’s pretty accurate.

Well if you're going to be like that about it, can you do me a thermal image of a fan in operation?


No.

But I can paint a thermal picture with numbers, if that helps.

Fire is on. Fan started turning when the cowl it sits on got to about 100. Base of the fan is that. Body of be fan, the rotating parts and the blades for heat transfer were about 45.

Fires running well now, on a reasonably low heat and the cowl is 180, fan base is around 145 and the other parts about 70.

All values in degrees C.

Hairyloon



Joined: 20 Nov 2008
Posts: 14871
Location: Today I are mostly being in Yorkshire.
PostPosted: Fri Feb 02, 18 12:07 pm    Post subject: Reply with quote    

Thank you. Very helpful. Looks like the 150°C cells will probably cope, which is handy 'cos I have one here (somewhere).
I don't suppose you are able to measure the top of the stand? Effectively the hot side of the cell. I imagine it's a bit tricky to do so don't go to trouble, but I'm curious about the rate of heat transfer up the stem compared to the heat lost from the stem, if that makes sense.

Nick



Joined: 02 Nov 2004
Posts: 33762
Location: Hereford
PostPosted: Fri Feb 02, 18 1:58 pm    Post subject: Reply with quote    

I’ll try and remember next time it gets cold and I’m here.

Hairyloon



Joined: 20 Nov 2008
Posts: 14871
Location: Today I are mostly being in Yorkshire.
PostPosted: Fri Feb 02, 18 8:51 pm    Post subject: Reply with quote    

As I said, don't go to trouble: is just curiosity now.

Slim



Joined: 05 Mar 2006
Posts: 4922
Location: New England (In the US of A)
PostPosted: Mon Feb 05, 18 9:35 pm    Post subject: Reply with quote    

Google must have remembered that I looked up stirling vs. thermoelectric stove fans. They've just suggested this scrapheap challenge DIY stove fan video to me (seems to be one of many out there): https://youtu.be/1u7POtVxtMI

Hairyloon



Joined: 20 Nov 2008
Posts: 14871
Location: Today I are mostly being in Yorkshire.
PostPosted: Tue Feb 06, 18 2:52 pm    Post subject: Reply with quote    

Slim wrote:
Google must have remembered that I looked up stirling vs. thermoelectric stove fans. They've just suggested this scrapheap challenge DIY stove fan video to me (seems to be one of many out there): https://youtu.be/1u7POtVxtMI


I thought it was a really clever Stirling engine when I saw the chainsaw cylinder. Disappointed to find it was just being a cooling device.

Did like his explanation of how the thermoelectric cell works.

Slim



Joined: 05 Mar 2006
Posts: 4922
Location: New England (In the US of A)
PostPosted: Tue Feb 06, 18 5:33 pm    Post subject: Reply with quote    

I was hoping he would use the pipe fitting that held the fan as a "chimney" with fan assist to draw air directly over the thermoelectric cell for better cooling the cool side. The fan still basically did that, I just wanted to see some extra flourishes I guess.

I also thought it was going to be stirling at first

dpack



Joined: 02 Jul 2005
Posts: 33288
Location: yes
PostPosted: Tue Feb 06, 18 8:06 pm    Post subject: Reply with quote    

a stirling that small might be a bit beyond scrapheap challenge.

scale matters when it comes to coefficients of friction, longevity of tolerences, etc etc.

my point is small and moving requires supergood engineering in general as well as in relation to energy harvest by mechanical means.
solid state stuff making leccy works well for small machines

pop a fan on the drive of a chainsaw and cut out most of the faff?

Mistress Rose



Joined: 21 Jul 2011
Posts: 9204

PostPosted: Wed Feb 07, 18 8:08 am    Post subject: Reply with quote    

I would agree with you Dpack. Having been fighting tolerances and coefficients of expansion most of my working life in microelectronics I understand the problem.

dpack



Joined: 02 Jul 2005
Posts: 33288
Location: yes
PostPosted: Wed Feb 07, 18 10:50 am    Post subject: Reply with quote    

rolex and t34 demonstrate the different approaches depending on scale. both are complex machines but one can be mended in a barn with a gas torch, half a dozen stout tools and a big hammer, the other needs a microscope, a cleanroom and a very steady hand.

Hairyloon



Joined: 20 Nov 2008
Posts: 14871
Location: Today I are mostly being in Yorkshire.
PostPosted: Wed Feb 07, 18 5:42 pm    Post subject: Reply with quote    

dpack wrote:
a stirling that small might be a bit beyond scrapheap challenge.

I don't know. I've got one here where the transfer cylinder is made from a coke can, and the power cylinder is made from a milk bottle top.
It wouldn't work as a stove top fan because it's largely made of cardboard...

dpack



Joined: 02 Jul 2005
Posts: 33288
Location: yes
PostPosted: Thu Feb 08, 18 10:57 pm    Post subject: Reply with quote    

umm. i still recon a stirling to power a tiny fan is watchmaking

however i see no reason a stirling could not pull a kva (hp ) or two off a domestic woodburner giving more than enough power to drive any hvac fans required. add one of elon's battery packs and the lights n pooter work.

heat and power on a household scale from wood is an attractive option for some situations.

as a scrap heap challenge creating a practical woodburner x stirling hybrid seems plausible at the 5 to 10 kg of logs, ie heart of a house, size.

proof of concept should be fairly easy but making it work in a way that isn't extreme steam punk in the middle of the house might need a bit of thought .
a nice bonus is the "waste" heat is right where you might need some low temp heat.

30 odd years ago i came across a scandinavian system of wood fuel open fire with powered hvac and heat exchanger built into a whole house system. it was very good at warming a house efficiently on a few sticks.
adding in the power side (with an excess of leccy and still using all the heat) would be the next gen.

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