Closed chamber Stirling engine generator.

[Groundloop]

@All,

Take a look at this video:

http://youtube.com/watch?v=kYKOjnCwmG8&feature=related

Groundloop.

[dutchy1966]

Hi groundloop,

I've been pondering about the same sort of stuff lately. I mainly came to the conclusion that a parabolic trough is too expensive/complicated for an amateur scientist. On the other hand Fresnel lenses are cheap and easily obtainable.
The question then becomes what best to do with the focussed sunlight. It has enormous heat potential. We can either use it through a stirling cycle as you suggested or use solar panels (not so efficient). I'm still looking at oscillating steam engines to use. The oscillations can then be used to generate power by a magnet/coil combo (as in your stirling design).

I have made a little drawing which shows a way to maximize the use of fresnel lenses in a for amateur doable way.

Maybe it is usable for your plans or it will give u some new ideas

btw the picture shows an evacuated solar tube in the center but it could also be the hot side of a stirling engine. The yellow lines are supposed to be the rays from the sun.....



regards

Robert

[tinu]

@Groundloop,

Late reply. I was out for dinner and I?m a bit lazy now so it won?t be a very elaborate answer.

First: I?m not an expert in Stirling engines, neither in thermodynamic ones. So, may views are subject to human errors and surely to various improvements.
Second: Pretty much like most endeavors, the burden rests on the inventor/initiator. This is said to take my views as coming from the side.

I deduce you?re from Norway. First issue would be to decide whether focusing the sun-light or not. It dry or very arid/desert area it seems more advantageous to vote for focus. But there are great disadvantages: tracking the sun (energy and money; good control mechanisms are needed), provide good mirrors often in not common geometrical shape (hard to manufacture and expensive) and keep those mirrors clean; increased risks (birds, fires, burns etc); very narrow window of high efficiency, easily affected by light clouds and other phenomena. I know that for Europe most solar water heaters are not-focused or just lightly focused using small mirrors behind collectors. My option would go into that. But if you decide to focus, well be it. However, on a large body that absorbs heat and transfer it to a sink (like a stirling engine does) 400-600Celsius will require large mirrors. How large? That can be told only after the engine is designed because it will give the amount of heat transferred from the hot to the cold side per each stroke. Also, the hot area of such setup shall be placed in vacuum for minimizing loses and also under some kind of one-way reflexive layer (but these can be bought as they are already manufactured and widely used for various purposes).

For power estimates, I'd go at a maximum of 1.2kW/sqm. It is highly arguable and subject to local conditions. That?s what I used so far. Assume 90% eff for mirrors and you have 1080W (maximum) focused on a given surface. Now a whole bunch of questions arise. Getting to the equilibrium temperature depends on each choice: surface area, color, heat capacity, heat transfer, black-body radiation. I?d go for simple experiments using a 1-2KW heater versus mirrors on a ?Stirling dummy?, starting from Q=C*Delta(T) and drawing a graph. It will go flat toward high temperatures, thus giving a better estimate about 400-600Celsius . My actual guess would be more like 200-300Celsius for a homemade setup.

How big is a 300W Stirling?
It depends on the working pressure. Higher the gas pressure, smaller the engine. It resides in p*V=N*R*T and W=p*Delta(V) as long as p can be approximated as constant.
http://youtube.com/watch?v=BBZDJn6B0cs might actually be around 300W (?) but I don?t think it will suit you.

The only issue I have is that the motor you drew above will not work. Please take a closer look at it. There is nothing to make the piston to move back and forth. You still need to provide a mechanism for that. Also, please have a look on Stirling theory and also at practical devices. There is not a single one that takes power from the displacer. Displacer is always powered (usually by the piston through a flywheel) and it is used to circulate part of the working gas between hot and cold side, thus ensuring the required cycling.  Not only that the displacer (which is not air/gas-tight in respect to the cylinder) is always powered by the main piston, but the main piston is as air-tight as it can be. But in your drawing, if I understand it correctly, the gas will simply pass through the space between the displacer and the cylinder if there is such space. Very little work is transferred by the almost freely passing gas to the displacer and this gas-flow is only temporarily (until thermal equilibrium is reached). No work.
On the other hand, if I misunderstood the drawing and there is not such space and you rightfully put the name ?piston? where it is, the piston will indeed be forced to move by the developing pressure inside the gas due to heating. The piston will indeed be pushed back when you heat the hot side and will do some work in the process but then it will stay there forever, or at least until the heating cease. You need a mechanism either to stop the heating or to increase the cooling, otherwise the piston will not move from that position.
So, either way I really don?t see how it can possibly work. That was the only issue I raised in my first post.

Guess we?ll talk more tomorrow. It?s already late here.

Cheers,
Tinu

[dutchy1966]

Hi groundloop,

You might wanna look at this nasa slide presentation about free piston sterling engines:

http://www.grc.nasa.gov/WWW/tmsb/stirling/intro_stirling/Slidepage.html

hope it is useful

regards

Robert

[AhuraMazda]

@dutchy
Could you please post whatever is there? I am told I need a NASA pass to look at the page.

AM