Personally, though I've seen improved performance using a proper regenerator, I have some doubts that it is the best option for improving performance.
One, because Robert Stirling noted that the most effective regenerator (just the channel around the displacer, between the displacer and the walls) had extremely tight clearance. So tight, infact, it leads me to conclude there was what amounted to an air bearing or air lock of sorts,around the displacer, which would act more like a complete air seal rather than a regenerator.
Also, for the regenerator to be useful there would need to be "excess" heat for the regenerator to capture. But maybe that "excess" heat could be more usefully employed by using a larger diameter piston to increase the power output in that way.
This is all, of course, in the realm of theoretical ideas or things I'd like to try or experiment with if I ever find the time.
Maybe compare some porous foam glass with steel wool, see which performs better
I've also been wondering if a porous foam glass displacer might perform better if the outer surface were sealed with something heat reflecting/insulating, like maybe a coating of hollow glass microspheres mixed with water glass. That would, presumably, reduce any potential regenerative effect but increase it's insulating properties My theory being that less heat absorbed/conducted by the displacer would result in more heat available for power production
IOW if the engine is running at less than peak performance with excess waste heat, a regenerator can help, but if already at peak performance, it could actually reduce performance.
I suspect that may be why, over the years, I've read instances of both. Some people report improved performance and others report reduced performance with the addition of a regenerator.
High temperature displacer
Re: High temperature displacer
While looking for grill cleaning bricks online, I saw that some smaller white ones were readily available locally at both Lowes and Home Depot.
I was out picking up some gutter pipe this afternoon, so grabbed a couple.
These are very light and permeable. Air can be blown through them, the cell structure is larger and more open, unfortunate, they do not stand up to high temperature very well at all, but fracture and crumble easily after even a slight heating with just an ordinary cigarette lighter.
https://youtu.be/thQSWdlYbf8
I was out picking up some gutter pipe this afternoon, so grabbed a couple.
These are very light and permeable. Air can be blown through them, the cell structure is larger and more open, unfortunate, they do not stand up to high temperature very well at all, but fracture and crumble easily after even a slight heating with just an ordinary cigarette lighter.
https://youtu.be/thQSWdlYbf8
Re: High temperature displacer
Making a small foamed glass displacer for this little model engine, from a gerbil chew toy was very easy and took just a few minutes using only a serrated kitchen knife as a saw to rough out the shape and some sand paper for the finishing touches.
The hardest part was sanding gently enough so as not to remove more material than necessary. Though the stuff is not particularly fragile, it sands down very easily and quickly.
I'll be needing to pick up, or send for some 1/16" stainless steel rod to finish. The original displacer rod is spot welded on and would be difficult to remove. Also it is probably worth saving so the different displacers can be swapped out for comparison. See if the foamed glass really makes a difference.
After running the engine for a while, then taking off the displacer cap, the stainless steel displacer was hot as a pistol. (I checked with a magnet that it was stainless).
The displacer was much too hot to remove from the engine with my bare fingers. I think replacing it with foamed glass could be a big improvement as it does not seem to retain or conduct any heat at all.
These gold colored engines, in general, overheat more easily and do not run nearly as fast or as well as the similar lower profile (often red or gray) metal engines that have aluminium displacers. I'm guessing because the aluminium sheds heat very rapidly, so doesn't conduct the heat as far (?) But replacing the aluminium with wood made a remarkable difference as far as the amount of heat required to keep the engine running, while it also ran just as well at high speed. The wood became charred though.
Still waiting for the big grill scrubbers for the stove fan.
The hardest part was sanding gently enough so as not to remove more material than necessary. Though the stuff is not particularly fragile, it sands down very easily and quickly.
- Resize_20221004_205509_9365.jpg (347.91 KiB) Viewed 3857 times
- Resize_20221004_205508_8536.jpg (260.54 KiB) Viewed 3857 times
After running the engine for a while, then taking off the displacer cap, the stainless steel displacer was hot as a pistol. (I checked with a magnet that it was stainless).
The displacer was much too hot to remove from the engine with my bare fingers. I think replacing it with foamed glass could be a big improvement as it does not seem to retain or conduct any heat at all.
These gold colored engines, in general, overheat more easily and do not run nearly as fast or as well as the similar lower profile (often red or gray) metal engines that have aluminium displacers. I'm guessing because the aluminium sheds heat very rapidly, so doesn't conduct the heat as far (?) But replacing the aluminium with wood made a remarkable difference as far as the amount of heat required to keep the engine running, while it also ran just as well at high speed. The wood became charred though.
Still waiting for the big grill scrubbers for the stove fan.
Re: High temperature displacer
Unfortunately the 4" X 4" grill bricks I ordered turned out to actually only be 3 1/2" X 3 3/4".
I was skeptical about the 4x4 in the first place, but I called to see if by some chance I got the wrong item and maybe there actually are some 4X4 ones available. The representative is checking and will call back, but I'm not keeping my fingers crossed.
At a minimum, they need to update the information on the website
I was skeptical about the 4x4 in the first place, but I called to see if by some chance I got the wrong item and maybe there actually are some 4X4 ones available. The representative is checking and will call back, but I'm not keeping my fingers crossed.
At a minimum, they need to update the information on the website
- Resize_20221005_160623_3382.jpg (162.85 KiB) Viewed 3843 times
Re: High temperature displacer
It also, unfortunately, does not stand up to high heat or direct flame as well as I had hoped.
https://youtu.be/XdvSDq_1PPM
The clear winner in that regard is the pet chew toys.
https://youtu.be/0FYNuj-Df7g
After sawing one of these small white chew stones up to shape it for use as a displacer, the resulting powder is very chalk like, and reminds me of the dust that results from cutting gypsum wallboard.
As gypsum is used as a foaming agent in some, but not all foamed glass, I'm wondering if the calcium content has something to do with the very high heat resistance.
Something to experiment with in the microwave kiln when I get the chance.
https://youtu.be/XdvSDq_1PPM
The clear winner in that regard is the pet chew toys.
https://youtu.be/0FYNuj-Df7g
After sawing one of these small white chew stones up to shape it for use as a displacer, the resulting powder is very chalk like, and reminds me of the dust that results from cutting gypsum wallboard.
As gypsum is used as a foaming agent in some, but not all foamed glass, I'm wondering if the calcium content has something to do with the very high heat resistance.
Something to experiment with in the microwave kiln when I get the chance.
Re: High temperature displacer
The rod I needed turned out to be 5/64 in. diameter.
Anyway, here is the foamed glass (made from the rabbit chew stone) displacer in action:
https://youtu.be/WuqTKv0oXn8
I think there is some improvement in power over the stainless. Not as dramatic an improvement as when replacing the aluminium displacer in the other model engine. SS is already OK as far as not conducting a lot of heat.
Incidentally, I'm using the "Superzilla" non-flammable lube on the piston. I also tried some gun oil ("Weapon Shield" brand) which also worked well.
I also tried using a shorter, piston that was a better fit in the cylinder (less of a tight fit) I had from another engine, without my ground down "rings" modification, and that worked just as well with the liquid lubricants. It seems the main culprit preventing the engine running was just the rather ridiculously long, very tight fitting power piston.
No explosions so far.
Overall, IMO, being able to use some fluid lubricants is a big improvement over being stuck with just using graphite.
Anyway, here is the foamed glass (made from the rabbit chew stone) displacer in action:
https://youtu.be/WuqTKv0oXn8
I think there is some improvement in power over the stainless. Not as dramatic an improvement as when replacing the aluminium displacer in the other model engine. SS is already OK as far as not conducting a lot of heat.
Incidentally, I'm using the "Superzilla" non-flammable lube on the piston. I also tried some gun oil ("Weapon Shield" brand) which also worked well.
I also tried using a shorter, piston that was a better fit in the cylinder (less of a tight fit) I had from another engine, without my ground down "rings" modification, and that worked just as well with the liquid lubricants. It seems the main culprit preventing the engine running was just the rather ridiculously long, very tight fitting power piston.
No explosions so far.
Overall, IMO, being able to use some fluid lubricants is a big improvement over being stuck with just using graphite.
Re: High temperature displacer
I was watching this video, as I'm intending to do some experimenting with running Stirling engines on hydrogen fuel (burning hydrogen gas that is)
https://youtu.be/LosIGdwELVU
I was curious about the byproduct of the reaction: a form of sodium aluminate: https://en.m.wikipedia.org/wiki/Sodium_aluminate
Down a ways on that Wikipedia article is mentioned that sodium aluminate is used in the manufacture of refractory bricks.
That got me thinking about my foamed glass, or foamed ceramic, high temperature displacer project(s).
Turns out, sodium hydroxide has been used as a foaming agent for making foamed glass: https://www.sciencedirect.com/science/a ... 9319301048
It is also interesting that the reaction itself produces a tremendous amount of heat while the hydrogen is being released.
My original thought or question was what to do with this left over solution of sodium aluminate.
Could the process be reversed? That is, could the sodium aluminate be somehow converted back into aluminum ?
If that were possible, it seems this could make a very dense method for storing heat energy to operate a Stirling engine. Heat from both the exothermic reaction as well as heat from burning the resulting hydrogen gas. All from a few bits of aluminum and lye solution.
Is this the same lye that can be made from wood ash as in soap making?
https://youtu.be/LosIGdwELVU
I was curious about the byproduct of the reaction: a form of sodium aluminate: https://en.m.wikipedia.org/wiki/Sodium_aluminate
Down a ways on that Wikipedia article is mentioned that sodium aluminate is used in the manufacture of refractory bricks.
That got me thinking about my foamed glass, or foamed ceramic, high temperature displacer project(s).
Turns out, sodium hydroxide has been used as a foaming agent for making foamed glass: https://www.sciencedirect.com/science/a ... 9319301048
It is also interesting that the reaction itself produces a tremendous amount of heat while the hydrogen is being released.
My original thought or question was what to do with this left over solution of sodium aluminate.
Could the process be reversed? That is, could the sodium aluminate be somehow converted back into aluminum ?
If that were possible, it seems this could make a very dense method for storing heat energy to operate a Stirling engine. Heat from both the exothermic reaction as well as heat from burning the resulting hydrogen gas. All from a few bits of aluminum and lye solution.
Is this the same lye that can be made from wood ash as in soap making?
Re: High temperature displacer
There is, it seems, the possibility of separating the sodium aluminate back into sodium hydroxide and aluminum powder by electrolysis:
https://chemistry.stackexchange.com/que ... -hydroxide
However, the result is aluminum dust that may settle to the bottom of the sodium hydroxide solution and this tends to react to form sodium aluminate once again.
Strangely though, this seems like it could actually be an ideal heat battery.
I'm not sure if the alumina will continue to precipitate as long as a current is applied. If so, perhaps it could be filtered out before the current is removed.
Or used as a battery, perhaps this would not be necessary. Just use a charge cycle when current is available, then generate current when it's not.
In other words, in a solar or wind energy storage system. When there is an excess of electricity, use electrolysis to separate out the aluminum. Then when power is needed just allow the reaction to occur producing more heat from the exothermic reaction and release of hydrogen fuel. The heat released, both from the exothermic reaction and the burning of hydrogen to power a Stirling engine generator.
If this is possible, I wonder what the efficiency of the full charge/discharge cycle would be.
I suppose that would depend on if the hot air engine is "wet" or dry.
https://chemistry.stackexchange.com/que ... -hydroxide
However, the result is aluminum dust that may settle to the bottom of the sodium hydroxide solution and this tends to react to form sodium aluminate once again.
Strangely though, this seems like it could actually be an ideal heat battery.
I'm not sure if the alumina will continue to precipitate as long as a current is applied. If so, perhaps it could be filtered out before the current is removed.
Or used as a battery, perhaps this would not be necessary. Just use a charge cycle when current is available, then generate current when it's not.
In other words, in a solar or wind energy storage system. When there is an excess of electricity, use electrolysis to separate out the aluminum. Then when power is needed just allow the reaction to occur producing more heat from the exothermic reaction and release of hydrogen fuel. The heat released, both from the exothermic reaction and the burning of hydrogen to power a Stirling engine generator.
If this is possible, I wonder what the efficiency of the full charge/discharge cycle would be.
I suppose that would depend on if the hot air engine is "wet" or dry.
Re: High temperature displacer
Electrolysis is either endothermic (absorbs heat) or exothermic (releases heat) depending on the voltage.
https://www.sciencedirect.com/topics/en ... 20produced.
https://www.sciencedirect.com/topics/en ... s-of-water
Not sure which link would work best.
Anyway I was just curious if any heat could be reclaimed from the electrolysis process as well, but generally heat is absorbed during electrolysis, which makes sense. (unless the voltage is kept low and carefully maintained at about 1.4 volts apparently, then some additional heat could be absorbed from the environment as described in the article)
Now that is super interesting. About 1.4 volts It looks like ?If the reaction would take place in the orange-shaded area (Fig. 1), the efficiency would be 100%, and water splitting would take place by absorbing heat from the environment.
https://www.sciencedirect.com/topics/en ... 20produced.
https://www.sciencedirect.com/topics/en ... s-of-water
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Not sure which link would work best.
Anyway I was just curious if any heat could be reclaimed from the electrolysis process as well, but generally heat is absorbed during electrolysis, which makes sense. (unless the voltage is kept low and carefully maintained at about 1.4 volts apparently, then some additional heat could be absorbed from the environment as described in the article)
Re: High temperature displacer
I'm thinking about using a vacuum chamber as a means for creating a super-lightweight high temperature (or normal as well) displacer.
Could a small vacuum chamber be set up INSIDE a microwave? The displacer fabricated in a microwave kiln inside a vacuum chamber inside a microwave.
Seems potentially possible, if the vacuum chamber and air lines could be made of suitable material to go inside a microwave.
The general idea could be applicable to a setting material like foam concrete, plaster, refractory cement as well without the kiln/microwave, just using a vacuum.
It would be necessary to avoid "overinflation" and the vacuum would need to be maintained expanded in a steady state until whatever material fully set.
https://youtu.be/qxWqAgliMmY
Could a small vacuum chamber be set up INSIDE a microwave? The displacer fabricated in a microwave kiln inside a vacuum chamber inside a microwave.
Seems potentially possible, if the vacuum chamber and air lines could be made of suitable material to go inside a microwave.
The general idea could be applicable to a setting material like foam concrete, plaster, refractory cement as well without the kiln/microwave, just using a vacuum.
It would be necessary to avoid "overinflation" and the vacuum would need to be maintained expanded in a steady state until whatever material fully set.
https://youtu.be/qxWqAgliMmY
Re: High temperature displacer
Not an entirely new idea apparently, in regard to foamed concrete at least.
https://www.sciencedirect.com/science/a ... 1821001719
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https://www.sciencedirect.com/science/a ... 1821001719
Re: High temperature displacer
I'm finally getting around to attempting to make my first king size microwave kiln.
None of the microwave kilns available to order were quite big enough for the displacer for the Van Arsdell engine restoration project.
Hopefully, if it hold together, I'll also be able to use it for making ceramic parts, or even entire engine bodies for small model ceramic and/or glass engines.
It is possible to mold or cast glass or possibly even metal in a microwave.
Flower pot coated with silicon carbide and water glass as DIY microwave kiln.
None of the microwave kilns available to order were quite big enough for the displacer for the Van Arsdell engine restoration project.
Hopefully, if it hold together, I'll also be able to use it for making ceramic parts, or even entire engine bodies for small model ceramic and/or glass engines.
It is possible to mold or cast glass or possibly even metal in a microwave.
- Resize_20230323_203147_7993.jpg (196.75 KiB) Viewed 3224 times
Re: High temperature displacer
I wanted to do a simple test to see how just a small pile of silicon carbide heated up in the microwave. The microwave kept shutting down. Apparently due to some safety feature.
Putting a cup of water in with the silicon carbide kept the microwave on, but then the silicon carbide would not get above about 350°F
This was resolved finally by making the pile of silicon carbide much bigger to absorb more of the microwaves, and this prevented the safety from tripping without the cup of water in the oven.
But then the plastic rotisserie melted down and had to be removed.
At that point the silicon carbide got up to 800°F but would get no hotter because the microwave kept cycling on and off.
To resolve this, I set the microwave to the popcorn setting, which kept it on continuously for 1 minute and 50 seconds. however with repeated heatings on "popcorn" one after the other the silicon carbide would still not get above about 800°F, but the glass on the bottom of the oven got just as hot, or hotter, and the bottom of the oven was glowing red hot, but not the silicon carbide itself.
I took out the glass part of the rotisserie plate as well and finally the silicon carbide heated up fully, somewhere above 1100°F as high as my infrared thermometer could go. The kiln needs to reach about 2500°F to melt glass or fire ceramics.
Apparently the microwave has two popcorn settings, low and high. I used the high setting and the silicon carbide got a good white hot easily in less than 2 minutes and I'm sure over 2000°F after 3 minutes (twice on the popcorn setting).
https://youtu.be/NVIjGw_7UyY
I'm testing now to see if the big kiln itself will get as hot.
After a few minutes the flowerpot made some noise and developed a few cracks but still holding together so far.
2:00 in the morning and the wife just got up asking what the smell was and if I was burning something.
The smell is apparently coming from the microwave oven itself, I think. it seems it was not designed to withstand the kind of heat being generated.
Putting a cup of water in with the silicon carbide kept the microwave on, but then the silicon carbide would not get above about 350°F
This was resolved finally by making the pile of silicon carbide much bigger to absorb more of the microwaves, and this prevented the safety from tripping without the cup of water in the oven.
But then the plastic rotisserie melted down and had to be removed.
- Resize_20230324_001837_7716.jpg (156.47 KiB) Viewed 3218 times
To resolve this, I set the microwave to the popcorn setting, which kept it on continuously for 1 minute and 50 seconds. however with repeated heatings on "popcorn" one after the other the silicon carbide would still not get above about 800°F, but the glass on the bottom of the oven got just as hot, or hotter, and the bottom of the oven was glowing red hot, but not the silicon carbide itself.
I took out the glass part of the rotisserie plate as well and finally the silicon carbide heated up fully, somewhere above 1100°F as high as my infrared thermometer could go. The kiln needs to reach about 2500°F to melt glass or fire ceramics.
Apparently the microwave has two popcorn settings, low and high. I used the high setting and the silicon carbide got a good white hot easily in less than 2 minutes and I'm sure over 2000°F after 3 minutes (twice on the popcorn setting).
https://youtu.be/NVIjGw_7UyY
I'm testing now to see if the big kiln itself will get as hot.
After a few minutes the flowerpot made some noise and developed a few cracks but still holding together so far.
2:00 in the morning and the wife just got up asking what the smell was and if I was burning something.
The smell is apparently coming from the microwave oven itself, I think. it seems it was not designed to withstand the kind of heat being generated.
Re: High temperature displacer
I'm afraid the TNT guys flowerpot kiln idea is not going to work. Not this size or type of pot anyway
The pot itself is getting roasting hot on the outside, absorbing more of the microwaves than the silicon carbide on the inside.
This is a thermal image of the pot sitting on the basement floor after I gave up and took it out of the oven.
At best it got up to about 600°F both inside and outside after more than 15 minutes. It went up that high after five minutes but then would go no higher. The big clay pot is just soaking up all the microwaves with little if any getting through to the silicon carbide.
Looks like I'll have to try something else.
The pot itself is getting roasting hot on the outside, absorbing more of the microwaves than the silicon carbide on the inside.
This is a thermal image of the pot sitting on the basement floor after I gave up and took it out of the oven.
- Resize_20230324_021836_6044.jpg (175.99 KiB) Viewed 3215 times
Looks like I'll have to try something else.
Re: High temperature displacer
Interestingly, after the would be kiln cooled down, some large portions of the silicon carbide and water glass interior broke away from the clay, almost in tact., but not quite.
I tried super glueing the pieces back together so maybe I could then use some more water glass to fuse it back together, but it's probably too far gone, and would be too irregular to be very useful.
The pieces do seem nice and solid though and easy to handle. It gives me confidence that the method used in that other video should work better
If he can handle it with bare hands, obviously it doesn't have to issue of soaking up the microwaves on the outside like the flowerpot.
https://youtu.be/rAIyLWEKt8U
- Resize_20230324_031745_5538.jpg (199.08 KiB) Viewed 3211 times
The pieces do seem nice and solid though and easy to handle. It gives me confidence that the method used in that other video should work better
If he can handle it with bare hands, obviously it doesn't have to issue of soaking up the microwaves on the outside like the flowerpot.
https://youtu.be/rAIyLWEKt8U