Has anyone seen one of these? (thermoacoustic Stirling)

Moderator: stan.hornbaker

Forum rules
Be nice!

Has anyone seen one of these? (thermoacoustic Stirling)

Postby ozzu » Thu Dec 14, 2006 6:03 am

http://www.stirlingengine.co.uk/productskta18.html

Anyone know how this works? Their explanation sounds cheesy...

here's another one of these stirlings:
http://www.geocities.com/mgmlab04/
ozzu
 
Posts: 2
Joined: Thu Dec 14, 2006 5:58 am
First Name: Hi
Last Name: There

Response to Has anyone seen one of these? (thermoacoustic Stirling)

Postby Brent » Mon Jan 01, 2007 11:45 am

I don't think that their explanation of how the engine works, is necessarily correct or complete, but these engines do work! One of our previous users built one and got it running as described here:
http://www.stirlingengine.com/bboard/q-and-a-fetch-msg.tcl?msg_id=00002M&topic_id=Model%20Stirling%20engines&topic=

I think these engines may be important. There are several examples of these running You tube. You may want to search for Lamina engines or thermoacoustic Stirling engines.

The name lamina is not descriptive and probably should not be used. I think someone meant to say that these engines also laminar flow engines and the person who heard this didn't hear the r at the end of the word.

All piston engines ever built of all types have various mechanisms to create a power pulse on the piston. That's what steam engines do, that's what gasoline engines do, and that's what Stirling engines do. Making a power pulse is the important part of any "prime mover".

The interesting and perhaps useful thing about these new types of Stirling engines (and they are Stirling engines) is that they create their power pulse without any moving parts. The engines that are described above do have a moving piston, connecting rod, and crankshaft, but that's all! They don't have any mechanical displacer inside them to move the air from the hot side to the cold side thus creating a power pulse. These engines create their power pulse without using moving parts and that's why they are interesting.

You can search for thermoacoustic Stirling engines, lamina engines, and pulse combustion for more information. Most of the interesting work on this subject has been done by Los Alimos National Laboratories.

Any time someone comes up with a method for creating a power pulse with fewer moving parts we should consider the possibility that this may become a useful type of engine.

Brent Van Arsdell
American Stirling company
-------------------------------
Brent Van Arsdell
American Stirling Company
Brent
 
Posts: 16
Joined: Fri Mar 10, 2006 2:03 am
First Name: Brent
Last Name: Van Arsdell

Response to Has anyone seen one of these? (thermoacoustic Stirling)

Postby Brent » Sat Jan 20, 2007 12:49 pm

There is an important Stirling engine book that you definitely need to buy and read. It's titled Thermoacoustics by G.W. Swift.




Buy a copy here Thermoacoustics by Swift.




Or read a review under the power producing forum. Review of Thermoacoustics by Swift.
-------------------------------
Brent Van Arsdell
American Stirling Company
Brent
 
Posts: 16
Joined: Fri Mar 10, 2006 2:03 am
First Name: Brent
Last Name: Van Arsdell

Response to Has anyone seen one of these? (thermoacoustic Stirling)

Postby spacifique1 » Wed Mar 07, 2007 8:43 am

A possible explanation of how a Thermoacoustic Stirling works.

WOW!

I learnt so much in so little time!

Indeed, I also think that Laminar-flow (can't be Lamina, must be a mistake) Stirling engines may be very important. It might be the most efficient Stirling engine because moving the displacer requires energy, and using energy means less energy at the output, therefore less efficiency.

I think that I have an explanation as to how they work.

Take a look at http://www.youtube.com/watch?v=p08_KlTKP50. It is a great visual of what Laminar flow is about.

You will notice that at the beginning of the experiment, the colours start to mix and that at the end of the eperiment, the colours are back to their original, unmixed condition.

Similarly, I think that the "air sections" inside a Thermoacoustic / Laminar-Flow Stirling do not mix and work side by side in a spring-type arrangement.

Please refer to http://www.stirlingengines.org.uk/thermo/fig2.gif to get a clear picture of what I'm trying to explain.

If you take a look at the test-tube in the laminar-flow engine, the regenerator (or reformer) is placed at the closed end of the test-tube. The heat source is then placed at about the middle of the test-tube where the regenerator ends. Therefore, a part of the regenerator is heated and the end of it is "cold". As in other Stirlings, the regenerator will be used as an "thermal accumulator", a bit like a capacitor is an "electrical accumulator" in an electronic circuit.

Now, take a look at the piston and the crankshaft. I will refer to the position of the crankshaft as 0,90,180,270 in degrees to indicate their position.

When the engine is not running, the piston is at the 0 position or 180 positon. Once heat has been applied, you start the engine and give it a small push. Assume that you turn the flywheel clockwise and that the piston is at the 0 position.

What happens next is very interesting. The piston moves out of the cylinder, towards position 90 and the volume inside the test-tube expands. The air at the closed end of the test-tube get colder due to expansion, and a vacuum is created. The flywheel goes back anticlockwise because the momentum is not enough to counteract the vacuum created inside the tube.You notice that when starting the engine, you never know what way it will end up turning.

When the piston is returning towards the position 0 anticlockwise, the air moves back towards the back of the test-tube. The cold vacuum is recompressed and takes back its original pressure. The air on the right-hand side of the heat source is also moving towards the back of the test-tube. This air is already hot and it goes through the regenerator. Going through the regenerator, it get even hotter. The pressure starts to build up at the end of the test-tube as a column of superhot air is pushing against a column of ambient temperature air(or cold air which is in the cold part of the regenerator). The cold air acts as a spring and pushes the hot air in the opposite direction, i.e towards the piston.

Meanwhile, the piston has been moving anticlockwise until it reaches position 270, or the innermost part of the cylinder. The pressure is now at its maximum inside the tube. The path of least resistance is towards the piston and the air column starts to push against it. The piston changes direction and now moves clockwise.

The piston moves under the effect of pressure until it reaches the 0 position, work is therefore done during this part of the revolution. The pressure stabilizes again inside the test-tube at that point.

The momentum of the flywheel now drives the piston further out of the cylinder. The air is now in its vacuum phase in the test-tube. I f the momentum is big enough, the piston will continue its movement clockwise and overcome the vacuum. Once the crankshaft goes past position 90, the piston is sucked back in by the vacuum.

The piston continues to be pulled towards the test-tube until it reaches position 180. From that point, the flywheel again drives the piston and the hot air in the test-tube again becomes superhot by passing through the regenerator. The piston is, again, compressing the air.

When the piston arrives at position 270, the compressed air starts acting on the piston and the cycle starts over.

You can verify this easily if you record the first milliseconds when the engine is starting, and then play it in slow-motion. The crankshaft swings back and forth until it finally goes past the horizontal axis.

Another thing to consider here is that for all this to happen, it takes some time. At the start, all the forces in the engine are in equilibrium. Nothing moves. When heat is applied, the air contained inside the test-tube becomes "hot", energy levels start to increase. But for the engine to start, there has to be that first impulse.

The impulse is very important because it starts the movement of the "air sections" in the test-tube. The engine is referred to as Thermoacoustic engine because it works exactly following acoustic principles. The energy in the test-tube can be thought of as a wave, or even better, as a spring.

Imagine the same engine, but instead of the test-tube and all its air, steel wool and air sections, etc...just think that the piston is connected to a spring. When the piston moves out, it pulls on the spring. When the piston moves in, it pushes on the spring.

The spring is in it relaxed state and the piston is in position 0.Nothing is happening.

Now give a small impulse to the flywheel. The spring starts to contract and expand. Eventually, it will stop moving.

Why?! Because a spring is good at absorbing energy. It has no energy to give out unless it has been compressed or expanded. Energy is lost in the metal, in the form of heat,etc... (You know what I mean...it's 2.00a.m here and i've got to work at 8.00a.m tomorrow morning! I don't want to get into more details about why springs are not perpetual motion machines...)

Therefore, the gases in the test-tube can be summarized as being a spring. It will push when it is compressed and pull when it is expanded.

The most important difference in this "improved spring", that the person who first made it does not/ did not understand, is that there is a way to add ENERGY to the system in the form of heat.

When the heat is first applied to the test-tube, the air inside starts to expand, just like the spring expands. Pull on the spring and it will pull you back, just like when the first impulse is given, the vacuum pulls back the piston in.

Now compress the spring, and it gathers energy, just like the air in the test-tube. The difference here is that the air will always have enough energy to push back, because it gathers energy from the heated regenerator.

The regenerator is exactly where the magic happens! It is the key to the system and makes it work.

Enough for me tonight...
If you need any more info, or maybe have some info about my comments, please let me know.

Stephane Pacifique
8.03.2007
Australia.

spacifique1@iprimus.com.au

These ideas are only my personnal understanding and should not be considered exact whatsoever. Please contribute to the idea, as to my knowledge, to this date, there are no explanations of how exactly this Laminar-flow Stirling works. Please do not use this explanation officially until proven correct!

P.S: If by any chance one of you, readers, have a job a MIT or some similar institutions, I would not decline an offer. thanks.





spacifique1
 
Posts: 2
Joined: Wed Mar 07, 2007 6:25 am
First Name: stephane
Last Name: pacifique


Return to Model Stirling Engines

Who is online

Users browsing this forum: Google [Bot] and 2 guests