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'[OT] Heat Powered Fans'
2005\02\17@123915 by Aaron

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How do these fans work?

http://www.lehmans.com/shopping/product/detailmain.jsp?itemID=306&itemType=PRODUCT&RS=1&keyword=fan

"Reduce hot and cold spots in your room. Fan powered by the heat of your
stove circulates air away from stove and throughout the room.
Ingeniously designed fan converts thermal energy into electrical energy.
Blade automatically increases speed as the stove gets hotter and is
specially designed to gently move a broad section of air. Unobtrusive
and virtually silent. Will amaze and intrigue guests - a great
conversation starter! No maintenance required. Aluminum body and
anodized brass blades, one-year warranty, made in Canada."

Neat idea, but way too expensive for my budget!  Would like to try to
make one though... :)

Aaron

2005\02\17@125854 by Alex Harford

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On Thu, 17 Feb 2005 12:40:44 -0500, Aaron <spam_OUTpiclistTakeThisOuTspambright.net> wrote:
> How do these fans work?

I saw one of those when I was picking up some wood stove parts for my
parents' cabin.

I think it's either a Peltier device or dissimilar metals generating
the electricity, but I can't say for sure.

http://www.mne.psu.edu/me415/spring04/mega/

http://www.study-center.com/femp/content/demo/basics/bdheat.htm

I'd like to make one too, one obstacle I can see is how to get wire
insulation that can stand up to a wood stove. :)

2005\02\17@130630 by Peter Johansson

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Aaron writes:

> How do these fans work?
>
> http://www.lehmans.com/shopping/product/detailmain.jsp?itemID=306&itemType=PRODUCT&RS=1&keyword=fan

Peltier junction would be my guess.

-p.

2005\02\17@131134 by Harold Hallikainen

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Along a similar idea, I've always wanted to adapt gas refrigerator
technology to make a solar powered air conditioner. The hotter it is, the
better it works! Should be great for Fresno, CA.

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\02\17@140708 by James Newtons Massmind

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www.massmind.org/other/spac
http://www.atsfry.com/Passenger/pass_ac.htm

---
James.



> {Original Message removed}

2005\02\17@144531 by Mike Hord

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> How do these fans work?

Stirling engine?  Looks a little small for a Peltier-motor combo.

The massive fins on top would certainly help to create a good
temperature differential to drive it.

Mike H.

2005\02\17@162450 by Russell McMahon

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O, for a *REAL* one

       http://www.visionengineer.com/env/solar_flue.shtml

               RM



> http://www.massmind.org/other/spac
> http://www.atsfry.com/Passenger/pass_ac.htm

2005\02\17@162453 by Russell McMahon

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>> How do these fans work?

> Stirling engine?  Looks a little small for a Peltier-motor combo.
>
> The massive fins on top would certainly help to create a good
> temperature differential to drive it.

It's almost certainly a single Peltier module sandwiched horizontally
between the hot and cold portions.
A Peltier module that requires 50 watts odd for heating/cooling will
provide power typically in the 1 to 5 watt range, when heated and
cooled optimally - which would be enough for this application.

Free analysis software here

       http://www.melcor.com/software.html



       RM

2005\02\18@032640 by Michael Rigby-Jones

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>-----Original Message-----
>From: .....piclist-bouncesKILLspamspam@spam@mit.edu [piclist-bouncesspamKILLspammit.edu]
>Sent: 17 February 2005 19:46
>To: Microcontroller discussion list - Public.
>Subject: Re: [OT] Heat Powered Fans
>
>
>> How do these fans work?
>
>Stirling engine?  Looks a little small for a Peltier-motor combo.
>
>The massive fins on top would certainly help to create a good
>temperature differential to drive it.
>

It mentions conversion of thermal energy into electrical energy so it's
almost certainly a thermo-electric device.  I doubt they would be able
to manufacture and sell a stirling engine/generator combination for that
price.

Regards

Mike

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2005\02\18@091601 by Mike Hord

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> It mentions conversion of thermal energy into electrical energy so it's
> almost certainly a thermo-electric device.  I doubt they would be able
> to manufacture and sell a stirling engine/generator combination for that
> price.

Ah.  I missed that bit.

Correct me if I'm wrong (and I may well be), but isn't this the kind of
situation for which a Stirling engine would be pretty good?  Far simpler
design, much more durable, and probably a higher efficiency?

Mike H.

2005\02\18@100335 by Michael Rigby-Jones

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{Quote hidden}

Yep, and stirling powered stove top fans were used ~100 years ago.  The
only reason not to use a stirling engine is cost.

Regards

Mike

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This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
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not make any use of this information, or copy or show it to any
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2005\02\18@102910 by Russell McMahon

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>> It mentions conversion of thermal energy into electrical energy so
>> it's
>> almost certainly a thermo-electric device.  I doubt they would be
>> able
>> to manufacture and sell a stirling engine/generator combination for
>> that
>> price.

> Correct me if I'm wrong (and I may well be), but isn't this the kind
> of
> situation for which a Stirling engine would be pretty good?  Far
> simpler
> design, much more durable, and probably a higher efficiency?

A Stirling engine could indeed be used in that application. You can
buy Stirling engine fans which run off a hot source which could
include a stove - the ones I have seen are made in India. They are
intended for moving cooling air and using, AFAIR, an oil lamp flame or
similar. The maximum theoretical efficiency achievable is the "Carnot
efficiency" = (Thot-Tcold)/Thot (temperatures in degrees absolute). In
practice Stirling engine s typically achieve 20% to 50% of Carnot.

Peltier modules, being semiconductor based devices, generally don't
like to exceed 200 C and some would prefer less. At 200C and say Tcold
= 50C Carnot efficiency is (200+273 - (50+273) / (200+273) = 150/473 =
32%. A Peltier module will typically get 2% to 6% when used as a
thermoelectrixc generator or about 5% to 20% of Carnot. I used 50C as
you have to cool the cold side and unless the heatsink has an
excellently low C/Watt drop you get a large temperature differential
between cold side and air temperature. In their case the "cold" side
is cooled by the air above a wood stove so it won't be overly cool.
Note that they specify an upper limit for the stove top. This is no
doubt to keep the Peltier hot side below 200C. There will be some
temperature drop between stove top and Peltier module. Fail to follow
their instruction just once and your fan may die.

A reasonably done Stirling engine in the same environment could run at
hotter temperatures and achieve a greater efficiency. Many small model
Stirling engines are exceedingly inefficient. To get decent
efficiencies you MUST have a regenerator (despite what some will tell
you*) and to get decent power densities you need to pressurise and/or
use a better working gas than air - typically Helium.  Hydrogen is
even better but has a nasty habit of diffusing out through anything -
even through steel walls given enough temperature and pressure.

* The regenerator may not LOOK like a normal regenerator as long as it
functionally IS one. It's job is to store heat energy or "coolth" as
gas transits between hot and cold sides. Without this the transferred
energy is "destroyed" (dissipated) on each half cycle and wasted.

Compared to a Peltier a Stirling solution is liable to be more
expensive to implement but potentially far more durable.


       Russell McMahon




2005\02\18@141409 by Peter L. Peres

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On Thu, 17 Feb 2005, Aaron wrote:

> How do these fans work?

I haven't seen those but there is a simple trick to make such a thing
using hollow pressurized blades with a little water or other volatile
liquid in each. the heat source is applied to one of the lower quadrants
of the fan wheel and the liquid in the blade that presents itself there
evaporates (under pressure!). This changes the center of gravity of the
wheel and it moves a 'blade' upwards (the hot blade moves up - the wheel
axis is horizontal). After setting up right (enough of the liquid must
stay a gas until the relevant blade is past the TDC of the wheel), it
will work probably not at amazing speed. Some damping is required to
prevent oscillations due to the liquid in the blades. I suppose that a
larger fan supplies its own damping. If you try to build such a thing
pay attention to pressurisation. The pressure in the hot blade can
become very large (use very little liquid if possible).

A solar powered device using a 5" concave mirror and acetone as working
fluid was planned by yours truly for last summer but postponed ;-) I
also think that a device based on phase change could be made using wax
or even solder as working fluid.

Peter

2005\02\18@151933 by Mike Hord

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> I haven't seen those but there is a simple trick to make such a thing
> using hollow pressurized blades with a little water or other volatile
> liquid in each. the heat source is applied to one of the lower quadrants
> of the fan wheel and the liquid in the blade that presents itself there
> evaporates (under pressure!). This changes the center of gravity of the
> wheel and it moves a 'blade' upwards (the hot blade moves up - the wheel
> axis is horizontal). After setting up right (enough of the liquid must
> stay a gas until the relevant blade is past the TDC of the wheel), it
> will work probably not at amazing speed. Some damping is required to
> prevent oscillations due to the liquid in the blades. I suppose that a
> larger fan supplies its own damping. If you try to build such a thing
> pay attention to pressurisation. The pressure in the hot blade can
> become very large (use very little liquid if possible).
>
> A solar powered device using a 5" concave mirror and acetone as working
> fluid was planned by yours truly for last summer but postponed ;-) I
> also think that a device based on phase change could be made using wax
> or even solder as working fluid.

Such designs a frequently found on "free energy" websites, usually with
the "blades" designed as old propane tanks.

Their efficiency is such that you would be better off using the solar energy
to grow food, eating it, and riding a stationary bike with the calories from
the digested food.  They are a cute trick, though.

Mike H.

2005\02\18@160354 by Peter L. Peres

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On Thu, 17 Feb 2005, Harold Hallikainen wrote:

> Along a similar idea, I've always wanted to adapt gas refrigerator
> technology to make a solar powered air conditioner. The hotter it is, the
> better it works! Should be great for Fresno, CA.

There would be this process:

http://homepower.com/files/solarice.pdf

not continuous, but I have references for its use on railway cars
(bottled gas flame powered for meat and produce refrigeration in
transit). This is one of those technologies that have been around for a
*long* time and were partially forgotten. The railway car references are
from an ancient Marks Handbook (of mech. eng.) and predate WW2 at least.

The homepower article has a single action system, the railcar coolers
had automatic switchover (two circuits, one was regenerating while the
other was cooling).

The cycle uses CaCl2 and Ammonia in a closed system (no pumps, no
compressor, no valves).

By the way, what is the refrigerent in the 'heat pipes' used in laptops
and power amplifiers etc. Is it a freon or something else ? They seem to
be under high pressure judging from the heavy duty tube construction.
References:

http://www.thermacore.com/pdfs/mini.pdf

an example product, for PC cpu cooling:

http://www2.technobabble.com.au/article211.html

This year is said to be the hottest that was ever recorded. I think that
there will be a lot of interest in solar equipment.

Peter

2005\02\18@174406 by Peter L. Peres

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On Sat, 19 Feb 2005, Russell McMahon wrote:

> Peltier modules, being semiconductor based devices, generally don't like to
> exceed 200 C and some would prefer less. At 200C and say Tcold = 50C Carnot

There are several thermoelectric semiconductor junctions that work at
higher than 200C:

http://www.nanothermel.org/public_main.htm

(excellent link with nice graphs and real life numbers)

Peter

2005\02\18@185013 by David Minkler

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Fluorinert from 3M.

Dave

Peter L. Peres wrote:

>
> By the way, what is the refrigerent in the 'heat pipes' used in
> laptops and power amplifiers etc. Is it a freon or something else ?
> They seem to be under high pressure judging from the heavy duty tube
> construction. References:
>
> Peter



2005\02\19@125305 by Peter L. Peres

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On Fri, 18 Feb 2005, Mike Hord wrote:

> Such designs a frequently found on "free energy" websites, usually with
> the "blades" designed as old propane tanks.
>
> Their efficiency is such that you would be better off using the solar energy
> to grow food, eating it, and riding a stationary bike with the calories from
> the digested food.  They are a cute trick, though.

Why are you saying that ? Remember the dipping bird trick that dips for
half a day into a small vessel with 2 ounces of lukewarm water (the
water cooling faster from heat loss to the environment than to the
bird) ?

Peter

2005\02\19@131506 by Bob Blick

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On 19 Feb 2005 at 19:54, Peter L. Peres wrote:

> Why are you saying that ? Remember the dipping bird trick that dips for
> half a day into a small vessel with 2 ounces of lukewarm water (the
> water cooling faster from heat loss to the environment than to the
> bird) ?

Actually the dipping bird has a fuzzy nose and head, the water clings
to it and cools through evaporation - the "engine" runs on the
temperature difference between the head and the butt.

Cheerful regards,

Bob

2005\02\20@121730 by Mike Hord

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> Why are you saying that ? Remember the dipping bird trick that dips for
> half a day into a small vessel with 2 ounces of lukewarm water (the
> water cooling faster from heat loss to the environment than to the
> bird) ?

Try hooking a load up to it.

The mechanical losses in such a system will completely overwhelm
the power you generate.  Most of those shifting-liquid-wheel systems
will never get above a couple of RPM.  Efficiency and driving a large
load demands higher speeds than such a device will provide.

Look, don't get me wrong.  I'm not opposed to "thinking outside the
box" in search of new energy sources, but the bottom line is that
TANSTAAFL.  Thermodynamics is a harsh mistress.

http://www.tinaja.com

Again, Don Lancaster has a lot of "good" things about
pseudoscience.  And if that doesn't work out for you, ask yourself
how much surface area your contraption has, and how much
power in the form of sunlight is delivered to the surface at your
location.  The product of the two is the MAXIMUM you'll ever get
out of the thing.  Again, chances are you're better eating and
pedaling, or at least making a windmill.  After all, the generating
mechanism would be the same as for a windmill, but a windmill
will probably capture more energy.

Mike H.

2005\02\20@163346 by Peter L. Peres

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On Sat, 19 Feb 2005, Bob Blick wrote:

> On 19 Feb 2005 at 19:54, Peter L. Peres wrote:
>
>> Why are you saying that ? Remember the dipping bird trick that dips for
>> half a day into a small vessel with 2 ounces of lukewarm water (the
>> water cooling faster from heat loss to the environment than to the
>> bird) ?
>
> Actually the dipping bird has a fuzzy nose and head, the water clings
> to it and cools through evaporation - the "engine" runs on the
> temperature difference between the head and the butt.

That's right but it runs better here if the water is lukewarm (very
humid summers). Also for it to work 'right' (depending on how it is set
up) the water should be slightly warmer than the air and the wet bulb
temperature slightly colder than the air, All three conditions are
fulfilled if the water is lukewarm (exposing the water pot - painted of
not transparent - to the sun is a good way to achieve that. That would
be a solar dipping bird (the dipping bird should be in the shade).

Peter

2005\02\22@025853 by Peter L. Peres

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On Sun, 20 Feb 2005, Mike Hord wrote:

> Again, Don Lancaster has a lot of "good" things about
> pseudoscience.  And if that doesn't work out for you, ask yourself
> how much surface area your contraption has, and how much
> power in the form of sunlight is delivered to the surface at your
> location.  The product of the two is the MAXIMUM you'll ever get
> out of the thing.  Again, chances are you're better eating and

Assuming I can make something 1% overall efficient It would produce
about 10W from 1 m^2 of collector (mirror or something else). The tiny
amount of energy is not so tiny and small gas expansion and turbine
engines exist, which make use of unusual work fluids to use the low hot
source temperature in solar devices. I was thinking of it as a
demonstration object and a tech toy.

Peter

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