large lamina flow build

[derwood]

After thinking about a large lamina engine build for over a year now, I finally decided to try it. My goal is to build a large version using off the shelf materials. I started by finding detailed plans for a test tube version and scaling it up. I am using an air cooled vw cylinder. 3.5 in. diameter and a 3 in. stroke. After about two weeks of trial and error I do have a running engine as of last night. My fly wheel is approx 8 to 10 pounds and it is running at about 120 rpm. I will share with you guys what I have learned so far. When building a large version I have found that that results are much easier to measure than with a test tube model. my only weak point is my piston which is made of polyester resin. It is very sensitive to heat and only allows me to test for about 10 minutes at a time. It starts to expand and then gets stuck. That is ok though, It is good enough to test with. I will eventually go to an al. piston with teflon rings. Ok, this is what I have learned so far. The heat tube material is regular emt electrical conduit. it has an ID of 3.25 in. and the wall thickness is is approx. 5/64 in. I thought it might be to thick but it seems to work fine for testing. I thought it had to be stainless steel or very thin steel. although I have some fine tuning to do, I have found that even with an engine of this size the heat tube length has to be within an inch of the correct length to even begin to run on it's own. Volume means everything. The heat tube volume to piston stoke volume ratio has to be very close to get it to show signs of life. You guys that build the test tube models and can't get them to run, just remember that a couple of mm of heat tube length means everything. The tube diameter does not seem to be as important. Although mine is running this ratio still needs to be fine tuned so that the power of the expansion stroke is matched to the power of the contraction stroke. I think that when this balance of power is achieved the engine will accelerate more and the fly wheel weight will not be as important. I have found that the closer I get to this balance of power the fly wheel weight can be lowered to achieve more rpm's. As far as steel wool goes, I stopped using it. The volume of the steel wool is almost impossible to calculate and does not seem to be of any benefit other than a volume fine tuning tool. I am currently using a piece of 3/4 in. pipe 2 in. long to connect the heat tube to the piston cylinder. This is referred to as the ckoke. I have not experimented with choke sizes yet but I will when I feel everything else is fine tuned. I don't know how critical the choke is but it seems to be a way to consolidate the hot gasses into a smaller area so that they can be cooled easier before entering the piston cylinder. I hope this helps some of you and inspires you to build some bigger versions. My engine requires no machining just welding skills. I hope to post some pics and video soon.

[Ian S C]

5/64" sounds OK for a mild steelhot end, if you get it too thin, it will droop when its heated. Stainless is stronger under heat, also it does not suffer from scaling, ordenary steel corrodes, and you end up with flakes of rust in side the motor. With stainless, .030" would proberbly be what I would aim for. Congratulations on getting it running, now the work starts, trying to see how much you can get out of it. Ian S C

[Bumpkin]

Congratulations derwood - it takes commitment to get a bigger engine going. Mine keeps getting covered with layers of other shop projects and dust. Could you be more specific about getting the volume ratio "close" as in what is the overall compression or expansion ratio? Operating temp ratio would be nice to know also, but lacking instrumentation, guesstimates would be useful. Looking forward to any further observations such as from different choke tubes, and thanks for posting what you've done.

[derwood]

I never Thought I could get a larger one running. As far as the ratio goes, Figure the volume of your cylinder diameter and desired stroke. Multiply that by 5.25. The answer should be the total volume of your heat tube and choke. This should get you very close. Make shure to leave a little bit of adjustment each way on your stroke.

[Tom Booth]

derwood,

I am very interested in your project as I think the Lamina Flow engine is one of the most interesting of the Stirling Engines due to its simplicity.

Also the fact that you have one running without the Steel Wool regenerator, which I assumed was an essential aspect of this type of engine.

I don't think that the thermodynamics of this type of engine is completely understood and there are some conflicting theories like some kind of acoustics is involved, which I tend to doubt.

How does the piston ever make a return stroke towards the chamber where air is being heated and presumably should be continually expanding ?

Any video yet ?

Please provide an update!

Thanks.

[Geoff V]

Derwood

I had hoped we would have heard more from you about your Large Thermal Lag engine by now, I can only guess you are suffering from 'pressure of work'.

Some years ago I built a single cylinder TL engine which works very well, but I wanted to investigate whether or not it would respond to being pressurised so I built a 90 deg vee twin version which is designed to be pressurised, various commitments and interests prevented the project being completed until now. My goal is to exploit the TL cycle by increasing the swept volume as you have done, improving the heat exchangers, and by raising the working pressure initially on air and later on He. Currently I am making some minor improvements to my vee twin, adding instrumentation and carefully logging the proportions of the pulse tube before testing begins. Having re-read your thread I noticed you have found that with your engine the pulse tube volume is best at around 5.25 x the swept volume, where as mine (measured today by filling with water from a graduated syringe) is just 1.875 x the swept volume. It may well be that the slotted heater and tubular cooler that I employ dramatically effects the ratio of the volumes?

I also came upon a very interesting report on TL engine theory which you may well find of value.

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

Looking forward to hearing of your progress

Geoff V

[Tom Booth]

I've been thinking lately that the critical element in this type of heat engine is not so much the volume of the chambers but rather the relationship between heat delivery to the engine and heat utilization by the engine.

To a great extent this would manifest as a ratio between the sizes of the heat delivery chamber and the heat utilization or dissipation chamber.

The reason I was thinking this is that from your description, your cylinders are made of steel right? (EMT Electrical Steel Conduit)

Steel conducts heat about 40X better than glass.

http://www.engineeringtoolbox.com/therm ... d_429.html

In a test tube (glass) engine, the steel wool "regenerator" would serve to transfer heat from the glass more rapidly and increase surface area for heat exchange with the air in the chamber.

A steel pipe is already conducting heat much better than glass, so this this extra heat conductor in the form of a steel mesh in the chamber is not essential.

For the engine to utilize the heat delivered, the sweep or throw of the piston must be long enough for the gas in the chamber to fully expand so that the kinetic energy in the gas is exhausted sufficiently to allow the gas to cool and contract (or be compressed). If all the heat delivered is not utilized then the piston will be stopped and forced back by the momentum of the flywheel due to too short a throw. The piston will come up against the gas which has not yet expended all its energy and so is still trying to expand.

In other words, the regenerator material may still be of benefit so as to speed up heat delivery and increase the rate of heat exchange but the throw of the piston would have to be adjusted (lengthened) accordingly so that the engine could utilize this additional heat. Alternatively the load on the engine might be increased. (The greater the load, the more work the gas does while expanding, the quicker its energy is expended).

So although this LOOKS LIKE there is a VOLUME ratio involved, I think that this is only coincidental. By adjusting the volume of one chamber or the other you are also adjusting the effective heat delivery (when adjusting the heat chamber volume) and heat utilization ( when adjusting the cold chamber volume, or length, presumably by adjusting the throw of the piston).

In other words, to maximize efficiency I think the length of the cold chamber (power cylinder containing the piston) as well as the throw of the piston, and possibly the load on the engine (if any) should be adjusted so that the piston will travel as far or slightly farther than its natural stopping point if it were not attached to anything (free piston).

Put another way, the distance the piston travels on the "power stroke" must be of sufficient length for the gas pushing the piston to fully expend or use up all its energy so that on the return stroke the piston is not working against the gas that has not used up its energy and so is still expanding.

[derwood]

After more testing I agree with your conclusions. Although I have found that the choke size is very important to achieve the proper lag/delay in pressure change between the two chambers. I am thinking about placing a large diameter valve (light weight) where the choke would be. The valve would have a stem that extends half way into the cold chamber. the piston would start to open the valve half way on the down stroke and would completely close half way on the up stroke. pressure on the hot side and contraction in the piston/cold side should keep the valve closed but a light spring might be needed. also if the engine is positioned vertical with the hot end up, gravity would keep the valve closed. I think this would increase power on the contraction stroke. I recently bought a lathe so I will now be able to try some of my ideas in the near future.

Darren Booth

[Ian S C]

Tom, with regard to heat conduction of steel over glass. With glass test tubes, the shape and thickness are what you get, theres not much that you can modify, where as with steel you can slow the lengthwise heat conduction by thinning the section between the hot and cold end thus causing a thermal resistance with the reduced cross sectional area. The thickness, as long as it is kept reasonably thin, matters little on the material as far as heat transfer goes, its just got to be able to withstand the temperature that is used on that engine. Ian S C

[Tom Booth]

... I have found that the choke size is very important to achieve the proper lag/delay in pressure change between the two chambers. I am thinking about placing a large diameter valve (light weight) where the choke would be.

This got me thinking about something you said earlier

The heat tube volume to piston stoke volume ratio has to be very close to get it to show signs of life.... The tube diameter does not seem to be as important. Although mine is running this ratio still needs to be fine tuned so that the power of the expansion stroke is matched to the power of the contraction stroke. I think that when this balance of power is achieved the engine will accelerate more and the fly wheel weight will not be as important. I have found that the closer I get to this balance of power the fly wheel weight can be lowered to achieve more rpm's.

As far as achieving a balance of power, the flywheel, the choke,...

I'm in favor of trying as many different things as possible so don't let me discourage you in any way, you should try it anyway, but the idea of adding a valve... I get the feeling this might disrupt the natural flow somehow. I'm wondering if you have seen this guys videos on You tube. His user name is "mower of doom". Not sure if he visits here or not but he has a very interesting series of videos of some Lamina Flow engines he built after he made the discovery, by accident, that it is possible to run a Lamina Flow Engine without a flywheel. Free Piston.

I would have thought that without a flywheel the piston would just shoot out of the cylinder. But apparently not.

What I found especially interesting is that he found that the piston came back on its own on the return stroke with such force that he found it necessary to install a rubber washer to prevent the piston from banging into the choke orifice.

In a later model, again free piston with no flywheel, he installed a spring for the same reason.

Talk about lowering the flywheel weight and increasing the power on the return stroke...

Anyway, here is the first video he made where he describes how he discovered this by accident. That he could run the engine with no flywheel. I'm kind of amazed that this is even possible.

[youtube]http://www.youtube.com/watch?v=DyPxNNJQo9M[/youtube]

[Ian S C]

Hi Tom, I like it, I wounder what would happen if the nut in the piston was replaced by a magnet, and a coil wound around the cylinder. You would need to make sure that the metal work was non magnetic. Ian S C

[Tom Booth]

Hi Tom, I like it, I wounder what would happen if the nut in the piston was replaced by a magnet, and a coil wound around the cylinder. You would need to make sure that the metal work was non magnetic. Ian S C

Look at his other videos. He's gone through several more incarnations of this engine. There are a few he runs with linear generators, again with no flywheel.

[youtube]http://www.youtube.com/watch?v=cAyw_dOioMU[/youtube]


He calls this one a Thermal Lag engine. I'm not sure what the difference is between this and a Lamina Flow. Is there a difference ? Anyway he runs the same engine with a flywheel, without a flywheel and with a linear generator

[youtube]http://www.youtube.com/watch?v=J9ILlx3XPZ4[/youtube]

[Ian S C]

Thanks Tom, thats quite interesting, I thought he'd have to put a load of some sort on it, It is only then that it becomes a motor, running free it is not generating any power except that to over come friction. Thats about the most simple little generator that could be built, I wounder how big it could be built, perhaps an inch bore, worth thinking of. I think Geoff may confirm my idea that this is actually a form of the TMG (Thermo-mechanical -generator), but using a piston instead of a metal diaphram. Ian S C

[derwood]

After several attempts to construct a large lamina flow engine (mostly failures), I have come to some intersting conclusions. Although mostly failures I have learned a few things. I have tried many different compression ratios, stroke lengths, choke sizes, piston cylinder cooling, etc....... Nothing seems to make much difference at all. One thing I have noticed is that with all of my attempts the engines did show signs of running but only after the entire engine got extremely hot (piston cylinder too). I have been using all steel construction making sure to use very thin steel for the heat chamber. I now realize that material selction is very important. pyrex tube or ss is for the heat chamber is recomended because it does not conduct heat very good. Many people say this is true because heat is not conducted lengthwise to the piston cylinder. If this was true then thin mild steel should also work. It takes quite a while for the heat to conduct to the piston cylinder when using thin mild steel but it just does not want to work. many people report that when using pyrex and ss the piston cylinder heats up very quickly but with steel it takes a very long time. I think that pyrex and ss work good because like all materials that conduct heat poorly, they are a very good insulator as well. Even though the thin steel does not cunduct heat down it's length very well it is not a good insulator. It could be that the air (shock wave) inside the engine needs stay very hot, right up until the point of entering the piston cylinder. The thin steel does not allow this, It cools the air prematurely. The temperature difference is very low by the time it reaches the cylinder. You might say it diffuses the shock wave. With the pyrex and ss the hot air is insulated and maintains a much higher temperature. The temp difference will be higher. This might explain why the piston cylinder heats up quicker with the pyrex. This also may explain why one of my engines actually ran. It was the only one that used a cast iron cylinder, perhaps this cylinder cooled the air a little better than the steel cylinders, just enough to keep a higher temp difference but barely enough to run. Although these conclusions may not be correct, my many hours of reading and testing do give them support.

[Geoff V]

Derwood

I have published the following link before but if you missed it, it's well worth reading.

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

I spent some time testing my vee twin pressurised TL engine and although I failed to detect any power rise when I raised the working pressure, I do get about 0.1w/cc at the crankshaft, which by my recconing, is very similar to the power density of a simple hot air engine.

The main lesson learnt, which is agreement with the attached article, is that the cylinder is the cooler and benefits from being shrouded by the piston for much of the working cycle. Unfortunately I incorporated my tubular cooler as a 'cylinder head' which cools the working gas too early in the cycle. This was confirmed when I ran the engine with the coolant pump off until the cooler temperature rose significantly and watched the power drop when the pump was switched on.

I've tried to publish some pictures of this engine but am yet again frustrated by the very limiting file size accepted by this forum, if any one is interested in some pictures, drop me a line with your email address.

GeoffV

p.s. I've uploaded some low resolution pictures in the Machined Engines gallery