Thermal wheels

[JamesThomas]

Thank you, Helioechidna, for posting your work.

I'm certain your way, way ahead of me on this, so I'm mentioning it only for my own entertainment that I can see how two or three of the very same wheels mounted on the same axes, with tanks offset could result in smooth rotation.

Remember seeing your video, or a similar video, some time ago, and for some reason was not so impressed as seeing it now. There seems great promise here, and it is not so high-tech that it would inhibit us only-basic-science-knowledge folks from experimenting with it.

It's very interesting, and will check out the yahoo group you mentioned. However, please keep us informed here as well if you can.

Thanks again.
j

[hansvonlieven]

G'day gearhead and all,

The use of gases instead of air may not be as good idea as one might think. In all the years of experimentation with Stirling engines many gases have been tried in an effort to increase the power of the engine. Air has proved to be superior to everything else. With your suggestion you have a similar application, I am certain the same applies here.

Hans von Lieven

[Helioechidna]

Hi again,

Thanks for your comments.
Yes this technology is simple enough for high school science to be applied and you'll get it to work.
You'll need to understand a few principles first.
Firstly, don't be fooled, this is not a Stirling engine.
Secondly, the idea that a low boiling liquid will respond to small temperature difference as a way of generating pressure will trick you into thinking along the lines that most have had about how this works.

A Stirling uses gas to expand and contract with temperature difference.
The fluid used inside one of these devices is chosen to be nearly ready to boil at a very specific temperature range.
At just above the boiling point the pressure shoots up quite quickly to nearly one atmosphere, at just below the boiling point the pressure drops to about a tenth of an atmosphere. The pressure change is much larger than simply heating and cooling a gas.

If you try this with any other gas in the system, the energy used to boil the fluid in the bottom chamber is almost cancelled out by the energy used to compress the gas in the top chamber.

The system is under reduced pressure and the only gas in the system is the vapour from the fluid alone.

Choosing a suitable fluid is critical.

Too high a vapour pressure and all you have is gas in the top chamber that is going to need compressing and waste energy. Also you are going to need thick walls to contain that pressure which is another waste of energy; getting heat to flow into and out of the system through such a large thermal mass.

The wheel in the video is an early attempt and some of it's flaws highlighted the sensitivity of the system to tiny heat losses. I went for a sausage shaped tank which has been tried by just about every experimenter, the problem with that is just as the fluid is about to be pushed up to the top tank, the tip of the tank begins to emerge from the bath and cool down stalling or slowing the engine.

It highlighted two things, the need for the fluid to be fully transfered before any of the tank emerges from the bath, and how sensitive the system is to heat flow. (and why I say heating with solar radiation alone is going to be difficult to get working well, small desk top models will turn with solar energy alone but large scale devices won't be efficient enough to justify their cost.)

Those priciples in the first post are there because of experience and my Chemistry background.
Any attempts at using bellows or radiators has been dreamt up before and only add complexity at no gain to efficiency.

I hope many of you build something similar and share your findings.

[hansvonlieven]

Gday Helioechidna and all,

I understand that this is not a Stirling engine, however what Gearhead proposed is to put a flexible barrier between the fluid and the gas and relying on the gas to push the liquid around as it were. This does make it the same principle as a Stirling motor. It is irrelevant here whether the gas pushes a liquid via a membrane or a piston.

My comment was purely in response to Gearhead's idea, which I incidentally think has merit, not to the original wheel per se.

Hans von Lieven

[Helioechidna]

I've uploaded a video to you-tube:

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

it's the small wheel running under load and an bit of it's evolution in design.
More food for thought.