large lamina flow build

Discussion on Stirling or "hot air" engines (all types)
Geoff V
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Joined: Thu Apr 12, 2012 11:49 am

Re: large lamina flow build

Post by Geoff V » Mon Mar 11, 2013 11:10 pm

Derwood

For the purpose of measurement and comparison, the capacity of your TLE is, bore area x stroke (swept volume), Hot air engine derivitives are normally categorised this way with a few exceptions such as, the vee twin alpha. Because the working volume in a vee twin alpha cannot be equal to the sum of the swept volumes (one piston is descending whilst the other is still rising) it is necessary to measure the maximum internal volume and the minimum internal volume and subtract one from the other.

Your engine is unquestionably about 420cc.

GeoffV

derwood
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Joined: Sat Dec 11, 2010 10:15 pm

Re: large lamina flow build

Post by derwood » Sat Apr 06, 2013 5:12 pm

I am reposting the free piston version of my lamina flow engine.

[youtube][/youtube]

DavesPlanet
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Joined: Thu Mar 14, 2013 9:38 pm

Re: large lamina flow build

Post by DavesPlanet » Fri Apr 12, 2013 11:06 am

Your youtube video of the free piston lamina flow engine is awe inspiring, thank you.

Forgive my ignorance, I scanned through the posts on this subject and I don't quite understand why you are heating the far end of a lamina flow engine. Everything I've read suggests it must be heated just at the edge of the regenerator on the side with the piston.

Do you have any numbers for the power possible from a Lamina flow engine vs a beta Stirling?

I am interested in using a heavy sealed membrane instead of a piston. This design just screams to be fully enclosed and run maintenance free with a linear alternator. I've been looking at different methods for sealing a beta Stirling with low maintenance parts but if the power is anywhere in the same ballpark then maybe this is the way to go. Your video certainly suggested some real power output.

I am not finding many resources available for designing a Lamina flow engine, and I have certainly not found a good animation describing the pressure waves and how this thing works. I'll dig through this thread in closer detail to see what nuggets of wisdom might be found.

Thanks again!
Dave

Ian S C
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Location: New Zealand

Re: large lamina flow build

Post by Ian S C » Sat Apr 13, 2013 2:36 am

Dave, theres two ways of making the hot end of a lamina flow engine, the one you are thinking of where the gap is between the steel wool, and the power piston, and thats where its heated. The other type, the steel wool is next to the power piston, and there is a tube through the steel wool to a space at the far end, and this is where it is heated. I have one of the latter type, its advantage is that more effective cooling may be applyed at the piston end of the motor, and I think this is the idea behind Derwoods motor--Wellone of the ideas. Ian S C

DavesPlanet
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Re: large lamina flow build

Post by DavesPlanet » Sun Apr 14, 2013 11:49 am

Concerning the far end heating, does the tube double as the constrictor ring? Still looking for google images of such a critter.

Where could I find design info for cylinder diameter, resonance chamber length and diameter, and constriction ring sizing?

Thanks.
Dave

derwood
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Re: large lamina flow build

Post by derwood » Sun Apr 14, 2013 1:29 pm

Sorry I have not posted sooner but I have been very busy lately. I am still making changes to the heat tube. I have had better success with other designs but if I hade the proper materials available I think this design, with some small changes would be the best. I would like to add that this design was inspired by Geoff's design. He posted some pics of his thermo lag engine somewhere on this thread.
Last edited by derwood on Sun Aug 11, 2013 2:18 am, edited 1 time in total.

DavesPlanet
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Re: large lamina flow build

Post by DavesPlanet » Sun Apr 14, 2013 2:14 pm

In an early post in this thread Geoff discussed experimenting with a pressurized version. It occurred to me that changing the pressure and composition of the working fluid in a Lamina would change the speed of sound and I would postulate that a working engine could stop resonating as the pressure was modified. Further, I would guess that an engine designed to work at a particular pressure could be fine tuned for maximum efficiency by adjusting the pressure up or down. Obviously this point is moot for your design as there is no counter-balance pressure short of sealing the reciprocating shaft.

derwood
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Re: large lamina flow build

Post by derwood » Sun Apr 14, 2013 3:47 pm

Dave,

I think that a diaphragm version would work well. The cylinder would probably have to be a large diameter and not very deep. The cylinder would need to taper quite quickly like a funnel. This would eliminate dead space in the cylinder and allow for a short but powerful stroke. The engine will find it's optimum stoke. if the compression ratio is in the right range and the air volume between the heat source and the cylinder head is not to great or small, you should get good results.

DavesPlanet
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Re: large lamina flow build

Post by DavesPlanet » Sun Apr 14, 2013 8:20 pm

Smaller bore heat tube increased power possibly due to better heat transfer? Yet regenerator does not help? Very interesting. From there the next steps might be heat fins on the inner surface of the heat tube or bundling seven very small heat tubes and seven restrictors in a nice round bundle driving one piston.

Has anyone ever released a gas simulator that would describe temperature and pressure waves? If it hasn't been done yet then I might have some interest in tackling it.

Dave

Geoff V
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Re: large lamina flow build

Post by Geoff V » Sun Apr 14, 2013 11:29 pm

Gentlemen

I must reiterate my dislike of the term 'Lamina Flow', these engines function due to a Thermal Lag, which is also present in the Stirling cycle but detrimental to the performance, and the gas flow within the engine is certainly turbulent, NOT lamina. The Thermal Lag can be demonstrated, as I have done, by changing the working gas from Air to Helium which having five times the thermal conductivity of Air, prevented the engine from functioning at all by reducing the Thermal Lag. I also believe I have demonstrated that there is very little Acoustic component, if any, as it would suggest a very small power producing speed range, yet my test engines will run from a few hundred rpm to 3150rpm off load and produce a fairly flat power curve.

Regarding the use of a diaphragm instead of a piston, it may well work, but I would anticipate a significant loss of performance for several reasons. Firstly, if the academics are correct,

https://biblio.ugent.be/input/download? ... OId=851101

the cylinder walls are the best location for the cooling surfaces because the are shrouded by the piston for much of the cycle. Secondly the pressure pulse would be diluted as much of the available energy would be consumed in deforming the diaphragm material.

I have no doubts, from past tests, that the slotted heat exchanger in my pulse tubes, are the main reason for their willingness to run so fast and produce some measurable power. Yet other details contribute, not least of all, the very thin walled outer tube (0.15mm) which reduces heat conduction along the pulse tube.

Regarding the use of multiple tubes, I have tried this with no success at all.

GeoffV

p.s A gas simulation would be very interesting, but way above my pay grade, so go for it!

Ian S C
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Location: New Zealand

Re: large lamina flow build

Post by Ian S C » Mon Apr 15, 2013 4:15 am

The way I see a diaphram working is for it to be a large diameter, and oscillating say 2 or 3mm at the most, maybe similar to the amount of movement in the TMG.
Roy Darlington had a name for the motor, he called it the "Whatisit" engine in a Model Engineer artical, andTed Warbrook wrote a little book, and I think he sold kits, and called his the "One Piston Engine", I just call mine number 9. Ian S C

DavesPlanet
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Re: large lamina flow build

Post by DavesPlanet » Mon Apr 15, 2013 11:51 am

Geoff,
regarding your helium experiment you suggest the reason a working engine could not be converted to helium is that helium overcomes thermal lag, but could it not be just as plausible that the engine ceased working because the speed of sound in helium is 3 x that of air?
Dave

Geoff V
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Re: large lamina flow build

Post by Geoff V » Mon Apr 15, 2013 10:25 pm

DavesPlanet wrote: could it not be just as plausible that the engine ceased working because the speed of sound in helium is 3 x that of air?
Having discussed this matter at length with a very close friend, Allan Organ, and with reference to the article from the University of Gent, I do not believe there is any significant acoustic component in the Thermo Lag cycle.

I say again, would there not be a limited speed range if there were an acoustic aspect? yet my TL engines have a wider speed range than my Stirling cycle engines.

GeoffV

vamoose
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Location: Australia

Re: large lamina flow build

Post by vamoose » Tue Apr 16, 2013 4:06 am

Hey Chaps,
I have been enjoying reading this thread allot, although I’m only just keeping up with what you guys have been discussing..
I am interested in hearing your opinion regarding this particular engine made by barumman,

He says it operates at an optimal oscilation frequency of 87 herts, and runs a linear alternater for its electrical output.

In your opinions, would you designate its design, a thermo acoustic, thermal lag, or lamina flow engine. Or are they all potentially/comparably the same?? If not, or if so, can one discern the reasons, why or why not??

From availiable information, Its designation is a 'Thermomechanical generator' originaly designed by E. H. Cooke-Yarborough 
http://en.wikipedia.org/wiki/Thermomechanical_generator

vamoose

Geoff V
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Joined: Thu Apr 12, 2012 11:49 am

Re: large lamina flow build

Post by Geoff V » Tue Apr 16, 2013 5:46 am

Derwood

Apologies for the diversion.

Vamoose

The Thermomechanical Generator is simply a very short stroke Beta Stirling cycle engine, short stroke because the displacer is held by a flat spring which limits its travel and very similar in operation to the Free Piston Beta engines developed by SunPower.

Therefore it is neither Thermal Lag, Lamina flow or Thermo acoustic.

GeoffV

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