Sat on top of a lit, showroom log burner was a metal gizmo supporting a small motorised fan.
No electrical connection visible but still moving a fair bit of air.
How? Thermocouple effect?
The metal mount was made up of perhaps 4 strips around 20mm wide and
200mm long. Curious!regards
It could have been a small thermoelectric Generator like this
There is also an explanation on the top link of this page
These have been in production for a few years, but never really made it to the wide open market. Don't know why. They work roughly on the same principal as a heat exchanger in a fridge.
It is the same phenomena, Seebeck effect, where the heat flux through a pair of junctions, one hot one cold, produces a small voltage. When you place a few such junctions in series the voltage is additive but you need many metal to metal junctions to give a Volt (~250 for nickel-iron junctions. Thermocouples use exotic alloys.
Modern Thermo Electric Generators tend to use bismuth and antimony semiconductors in TEGS, these need far less junctions to produce a decent Voltage. Caterpillar are developing a large TEG that runs in the exhaust of a lorry, they say they get a few % conversion but with
500kW(t) dumped out of the exhaust a few % is worth having.The sort of thing I think you saw is a TEG made by running a Peltier effect cooler in reverse. These things have become very cheap as 12V beer coolers and even cpu coolers have come into mass production. I've taken one out of a fridge and it develops 2V at 100C temperature difference. One disadvantage of a TEC used as a TEG is they cannot stand high temperature compared with a normal TEG. The ecofan gets around this by having a bimetal strip to decouple the hot side from the stove heat. We've had a lot of discussion about these recently for small cook stoves where the fan effect is very useful for adding turbulence for good combustion.
AJH
Yeah. What he said. :-)
Forgot to add. It could also have been just the convection of hot air passing the fan that caused it to spin. The bit you thought was a motor housing, could actually have been a housing holding a swivel stud that holds the fan straight.
Thats what I reckon. Very popular in Germany are Xmas decorations that revolve, powered by the heat rising from a candle causing a fan to spin.
Like the old coal effect electric fires with two red bulbs and two little fans above which generated a flicker...
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Tim Lamb saying something like:
Thermo-electric generator powering a small DC motor. Not very powerful but enough to move sufficient air around in a small space to be very effective. I saw one sitting on top of a narrowboat log stove, working very well at its job.
In message , BigWallop writes
Presumably the cold side is room air.
Log splitter home BTW.
regards
In message , Grimly Curmudgeon writes
Sort of mechanical *boot strapping* but interesting nevertheless.
regards
Yes. 60 odd quid, mind you!
Huh! A bit like the boiler prices. I'll bet they are not on 16 week delivery.
regards
Sounds like it is similar to one of these.
G.Harman
In message , snipped-for-privacy@yahoo.co.uk writes
From other replies, I decided I must lead a very sheltered life:-)
regards
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