Absolute Newbissimo question.

[Mr.Zeph]

Hi all!

I'm considering creating a stirling engine for (at the moment) the single purpose of driving a fan in a solar heater as seen in this youtube video

http://www.youtube.com/watch?v=bRZvAAqzXIw

My understanding is that the Stirling operates by temperature differentials: one side hot, the other side cool, the larger the discrepancy, the faster the engine runs (more or less).

I live in a very cold climate, and so, with a solar heater easily running above 100 degrees F (37C+), my question is whether I can "embed" this stirling engine into the casing of the solar heater, if I were to have some sort of heat-sink that protrudes from the back of the box. Hot inside, bloody cold outside should allow for the temp differential.

The questions really boil down to:

* Is this feasable?
* Would the high internal temperature likely destroy my little engine? I'm not a machinst, so I'd most likely be working with tin cans and such.
* Would the engine generate enough power to either draw in cool air, or push out the hot air? (I haven't calculated the volume of air yet (let us assume that 48 inches, by 36 inches by 10 inches deep will yield 17280 cubic inches, more or less).

If this is reasonably do-able, I think I'll start over the weekend, if not, you're saving me a lot of time, the fun can wait until a bit later :)

Thanks

[PKM]

Hi Zeph,

I think the answers to your questions boil down to yes, no, probably not much. A stirling engine runs on a temperature difference- the bigger that difference, the more power the engine can get. Simple tin-can engines are inefficient and need a high temperature difference, and it's a lot easier to raise the temp of the hot end 100 degrees with a flame than cool the cold end that much.

Low temperature differential engines only need a difference of a few degrees or tens of degrees, so can easily run on ice at room temperature. If we assume your "bloody cold" outside temperature is below freezing, that gives you a difference of about 40-50 celsius- easily enough to run a well made tin can LTD engine. You'll probably need low-friction seals, a wide cylinder and a light displacer, but that temperature difference should be usable.

37C is not a high temperature, even for a simple can engine. Remember most people's first tin can engines run off flame power, so over 100 degrees C, and some will even run over a gas burner with one whole end glowing red hot. In this case high temperature epoxy (JB Weld or similar) and automotive silicone are your friends, but if your "hot side" will be at body temperature, you needn't worry.

Power-wise, the friction in your engine will determine how much you get out of it. A simple can engine will easily run a computer CPU fan, but dont expect it to drive a 15 inch box fan.

[jimlarsen]

You could get a little air to move, but those are big panels. I small LTD engine would only give you a little bit of a boost beyond what you probably get with the natural effect of letting the hot air rise.

Another thing to consider is that most Stirling engines will not start themselves. A Ringbom design will. But most others need a push to get started.

[Mr.Zeph]

<begin Wrath of Khan shot>Noooooooo!</end shot, hide sobbing actor>

Well, there goes a very cool idea! Oh well, I'm still fascinated by these little devices, and eventually, I'm sure I'll get to making some, but for now, then, I guess it's the old high-tech method, probably solar. The whole point of this for me is to avoid using grid energy. If only I had a practical use for the Stirlings, I'd have a great excuse :)

[Mr.Zeph]

A Ringbom design will. But most others need a push to get started.

Doesn't this:

http://www.youtube.com/watch?v=0Dbc8_aFXw0

violate some "limitations on cool" law, somewhere?

I must take a machinist course.

[Mr.Zeph]

Additional question: Would the sterling work if it were inversed? That is, machine at the bottom, heat at the bottom, cold on top (assuming that it is suspended).

[jimlarsen]

Many Stirling engine designs are reversible. Some are not.

[Ian S C]

Hi Mr Zeph,I saw the Ringbom engine mentioned, that can be quite a simple engine, but unless you get it spot on (I have'nt yet), it can be quite noisy, the most famous engine of this type is 'TAPPER', I'v built 3 of them, but would really like to know the correct ratio between the displacer and the displacer shaft.
Another reversable engine is the 'One piston"-Thermo Acoustic-Laminar Flow, or Lag Engine, I think every one has a different name for it, you can't get anything much simpler. these two are the only ones I,v come across so far that are simply reversable. Ian S C