It was suggested, after I posted this video on a science forum, that because it is just a video, the information is unreliable.
https://youtu.be/GFfMruoRMGo
The video was produced by Phillips Cryogenics. It seems to me nothing less than authoritative.
Nevertheless, what I posted the video for was the couple times near the start of the video where it is mentioned that a Stirling engine and a Stirling cooler rotate in the same direction.
I don't have much experience with using a Stirling engine as a cooler by driving it with a motor, but I always had the idea from somewhere that it was not necessary to drive the engine in reverse, but rather, to work as a cooler, it is turned in the same direction as it runs as an engine.
I've never tried running a Stirling engine as a cooler myself, but I believe I read a few posts in the past where others have.
So I would like to ask, from anyone who has experience with this, is this video accurate when it states that a Stirling engine AND cooler both turn in the same direction?
Also, I was wondering, do the hot and cold sides of the engine stay the same? That is, when driven by a motor and used as a cooler, is the cold side of the engine also the cold side of the cooler and the hot side the hot side, or are the roles reversed?
Thanks in advance, if anyone can confirm or clarify these points.
I know some Stirling engines will run in either direction, so, I'm not sure how that might factor in. I assume these types of engines will also work as coolers if driven by a motor in either direction?
Stirling engine and cooler?
Re: Stirling engine and cooler?
"Also, I was wondering, do the hot and cold sides of the engine stay the same? That is, when driven by a motor and used as a cooler, is the cold side of the engine also the cold side of the cooler and the hot side the hot side, or are the roles reversed?"
Watching the video, I'm not entirely sure what it says is 100% applicable to my little LTD engines.
In these little engines there are not really separate and distinct compression and expansion spaces
When applying heat to top of the engine (in the video) the opposite side (bottom).is the cold side. As a cooler, though, heat is drawn in from the top also, but rather than the bottom being colder, the video states that "heat does develop" to be cooled by a water jacket
I don't think there is exactly separate expansion and compression spaces in the video engine either as it appears what are being called such are joined by tubes through the regenerator.
There is rather a compression phase when heating occurs and an expansion phase when cooling occurs, and the majority of the gas is at either one end or the other but not such a clear cut division.
There is also, what is doing work on what at which phase?
The gas does work on the piston or vice versa. In the LTD engine this is somewhat complicated in that it is not hermetically sealed, so there is also the factor of the outside atmospheric pressure doing work, or being worked on.
It was after imagining an engine running, and trying to visualize precisely what was going on throughout the cycle that I came to the conclusion that insulating the cold side might just allow the engine to run cooler and more efficiently. This, apparently, by experiment, has turned out to be true. Though until I get some temperature probes, that internal cooling of the sink is taking place is not proven, though I don't really see any other explanation for why an engine would run at a higher RPM with the sink covered by insulation.
Watching the video, I'm not entirely sure what it says is 100% applicable to my little LTD engines.
In these little engines there are not really separate and distinct compression and expansion spaces
When applying heat to top of the engine (in the video) the opposite side (bottom).is the cold side. As a cooler, though, heat is drawn in from the top also, but rather than the bottom being colder, the video states that "heat does develop" to be cooled by a water jacket
I don't think there is exactly separate expansion and compression spaces in the video engine either as it appears what are being called such are joined by tubes through the regenerator.
There is rather a compression phase when heating occurs and an expansion phase when cooling occurs, and the majority of the gas is at either one end or the other but not such a clear cut division.
There is also, what is doing work on what at which phase?
The gas does work on the piston or vice versa. In the LTD engine this is somewhat complicated in that it is not hermetically sealed, so there is also the factor of the outside atmospheric pressure doing work, or being worked on.
It was after imagining an engine running, and trying to visualize precisely what was going on throughout the cycle that I came to the conclusion that insulating the cold side might just allow the engine to run cooler and more efficiently. This, apparently, by experiment, has turned out to be true. Though until I get some temperature probes, that internal cooling of the sink is taking place is not proven, though I don't really see any other explanation for why an engine would run at a higher RPM with the sink covered by insulation.
Re: Stirling engine and cooler?
Thanks, that helps.Bumpkin wrote: ↑Wed Aug 12, 2020 11:25 am There was this from Ian some years back:
viewtopic.php?f=1&t=1014&p=3861#p3861
Bumpkin
It confirms what the video was saying, from someone who has some actual experience.
It doesn't really explain my observations, or experiment, insulating the sink, increasing RPM. I don't think. Or does it?
What I was thinking is that when being heated and the air is expanding, the heat/kinetic energy, is transferred to the piston/crank/flywheel, then for a moment, the engine operates by being driven by the momentum of the flywheel, as if driven by a motor, like a Stirling cooler.
It seemed easier to imagine this ten years ago. Now my brain seems to be getting a bit fuzzy on the subject.
A Stirling cooler, though, still produces heat that needs to be gotten rid of at the "sink", or water jacket.
What I thought, ten years ago had to do with converting heat into work. (so the absence of the heat converted to work, leaves "cold")
I think that if my little engine is running as cool as it seems, then perhaps it could run even cooler with some type of external load. That was part of my brainstorm ten years ago anyway. I think it still makes sense.
Re: Stirling engine and cooler?
I created this diagram of the Stirling engine cycle - reinterpreted somewhat, according to my theories and observations regarding how a Stirling engine ACTUALLY operates.
Or, rather, how I've personally decided that I think it operates.
I've done an enormous amount of reading, and have also engaged in long drawn out debates on various Science forums, none of which actually proves anything, but I needed to have this diagram in order to explain my idea about what I think, or theorize, is how a Stirling engine must actually work, In my opinion, for a recent discussion on a Science forum.
Having gone to all the trouble of producing it, I thought I might just as well share it here, and this seems to be as good a thread as any, though I've considered also posting this to my Thermodynamics, and/or Tesla discussions here.
Anyway, please feel free to comment, criticize, refute, offer alternative explanations, point out problems, inconsistencies, errors etc. I won't be offended. Not too much anyway, I've been getting some very harsh criticism on this theory for over a decade already, and have pretty thick skin anyway.
Of course cheers and adulation are welcome as well.
Sorry this is not a high quality graphics or full animated 3D CAD image or something, just a sketch using Microsoft Paint program but its a start.
I am reserving copyright, or maybe call it copy left, Creative Commons, just because if this turns out to be significant, or experimentally verifiable, it would be nice if I received some recognition for it.
Without further ado;
Or, rather, how I've personally decided that I think it operates.
I've done an enormous amount of reading, and have also engaged in long drawn out debates on various Science forums, none of which actually proves anything, but I needed to have this diagram in order to explain my idea about what I think, or theorize, is how a Stirling engine must actually work, In my opinion, for a recent discussion on a Science forum.
Having gone to all the trouble of producing it, I thought I might just as well share it here, and this seems to be as good a thread as any, though I've considered also posting this to my Thermodynamics, and/or Tesla discussions here.
Anyway, please feel free to comment, criticize, refute, offer alternative explanations, point out problems, inconsistencies, errors etc. I won't be offended. Not too much anyway, I've been getting some very harsh criticism on this theory for over a decade already, and have pretty thick skin anyway.
Of course cheers and adulation are welcome as well.
Sorry this is not a high quality graphics or full animated 3D CAD image or something, just a sketch using Microsoft Paint program but its a start.
I am reserving copyright, or maybe call it copy left, Creative Commons, just because if this turns out to be significant, or experimentally verifiable, it would be nice if I received some recognition for it.
Without further ado;
- Stirling_engine-cooler_by_Tom_Booth_CC.png (55.61 KiB) Viewed 9167 times
Re: Stirling engine and cooler?
My contention here, which I've been speculating on for some time, on this thread for example: viewtopic.php?f=1&t=478 back in 2010, is that there is more to how a Stirling engine operates than just taking heat in on one side and getting rid of it on the other. Instead there is what is referred to as "adiabatic expansion" and/or "adiabatic cooling", when a gas does work to drive a piston in an engine at a speed that is too fast for what might be called the "normal" heat transfer to the sink.
Heat added to the gas inside the engine, in other words, is transformed into the mechanical motion of the engine itself.
A transfer of the gaseous molecular motion of the air particles (one form of kinetic energy) takes place, resulting in the kinetic motion of the engine.
Some, I am informed, consider this idea to be entirely contrary to the second law of thermodynamics. be that as it may, I find this conclusion inescapable, that is, I cannot come up with any better explanation for certain observations.
It is also quite in accord with the first law of thermodynamics regarding conservation of energy.
Heat added to the gas inside the engine, in other words, is transformed into the mechanical motion of the engine itself.
A transfer of the gaseous molecular motion of the air particles (one form of kinetic energy) takes place, resulting in the kinetic motion of the engine.
Some, I am informed, consider this idea to be entirely contrary to the second law of thermodynamics. be that as it may, I find this conclusion inescapable, that is, I cannot come up with any better explanation for certain observations.
It is also quite in accord with the first law of thermodynamics regarding conservation of energy.
Re: Stirling engine and cooler?
I think you are getting overly caught up with the theory of work. Yes, doing work converts heat-energy into kinetic-energy, however generally speaking such processes live in the 20% - 50% efficiency range, so the remaining heat-energy must be removed from the system, or it will become impossible for the heater end to add any energy to the system. Personally, I believe that you are correct in saying that a heat sink at the cold end isn't strictly necessary, but the kicker is that it IS ultimately necessary if your system is less than 100% efficient, even by 0.1%
Re: Stirling engine and cooler?
If you have to remove heat to make room so you can add heat, the problem is Improper load balancing.MikeB wrote: ↑Mon Jun 21, 2021 9:05 am I think you are getting overly caught up with the theory of work. Yes, doing work converts heat-energy into kinetic-energy, however generally speaking such processes live in the 20% - 50% efficiency range, so the remaining heat-energy must be removed from the system, or it will become impossible for the heater end to add any energy to the system. Personally, I believe that you are correct in saying that a heat sink at the cold end isn't strictly necessary, but the kicker is that it IS ultimately necessary if your system is less than 100% efficient, even by 0.1%
Re: Stirling engine and cooler?
Maybe I didn't explain that well - the basic operation of any Stirling involves repeatedly changing the temperature of the working fluid. That cannot happen if the temp of the working fluid reaches the temp of the hot end. Unless the energy removed through work is 100% then either the fluid will eventually reach infinity, or it must be removed from the cold end.
Re: Stirling engine and cooler?
Personally I don't believe in the whatever so-called law that supposedly requires heat to pass through a Stirling engine to the cold side.MikeB wrote: ↑Thu Jul 08, 2021 5:05 amMaybe I didn't explain that well - the basic operation of any Stirling involves repeatedly changing the temperature of the working fluid. That cannot happen if the temp of the working fluid reaches the temp of the hot end. Unless the energy removed through work is 100% then either the fluid will eventually reach infinity, or it must be removed from the cold end.
Heat enters the engine and is either utilized or returned to the hot side or regenerator.
The only reason, IMO for heat to be eliminated to the cold side is more heat being supplied than is needed for whatever given amount of work the engine is doing.
Heat being added to expand the air, followed by heat being removed to contract, or allow the air to be more easily compressed, is not actually how a Stirling engine works. That is 1800's theory based on observation of how water wheels operated and really only applies to water wheels, not heat engines.
Heat engines do not work by allowing heat to pass through the engine, they work by converting heat into other forms of energy. That it is a requirement for SOME heat to pass through the engine is just a lingering misconception. There is no such necessity.
A Stirling engine can use more than the supplied heat per cycle, which can result in a gradual cooling of the engine.
Re: Stirling engine and cooler?
As can be seen here; all the way back in 2006, my first post to this forum, I had already done a lot of reading through the forum and other information on Stirling engines, and had FULLY ACCEPTED that a Stirling engine worked by simply heating and cooling a gas in a canister as rapidly as possible and that that was all there was to it.
viewtopic.php?f=1&t=77
It was only after a great deal more effort at building engines, reading and observing and figuring and experimenting that I began noticing various anomalies that made the conventional explanation, not only incomplete but literally impossible.
Mostly, conductive heating and cooling is a gradual, slow process. Even a very lumbering low RPM Stirling runs too fast for simple conductive heating to be much of a factor in getting rid of all the heat being added.
There are many other clues to what's really going on, but cooling by transforming heat into work is the essential means through which a heat engine operates.
viewtopic.php?f=1&t=77
It was only after a great deal more effort at building engines, reading and observing and figuring and experimenting that I began noticing various anomalies that made the conventional explanation, not only incomplete but literally impossible.
Mostly, conductive heating and cooling is a gradual, slow process. Even a very lumbering low RPM Stirling runs too fast for simple conductive heating to be much of a factor in getting rid of all the heat being added.
There are many other clues to what's really going on, but cooling by transforming heat into work is the essential means through which a heat engine operates.
Re: Stirling engine and cooler?
When the piston moves out, the gas is expanded and cooling results. But simple expansion cooling is only part of the equation.
https://youtu.be/PMKPZuCj9a0
https://youtu.be/PMKPZuCj9a0
Re: Stirling engine and cooler?
To liquefy air requires extremely cold temperatures. Air liquifies at negative 318°F
There are various processes used to get air to such cold temperature, one being the Linde process, which involves simple expansion, as in the previous video
https://youtu.be/HmGDnaKZxxU
The air is first compressed, then allowed to expand. Very high compression is used around 100 atmospheres which is far higher than can be reached in a Stirling engine, but the process is the same. A Stirling engine simply alternately compresses air, then allows it to expand.
In the above air liquefaction process it was found that compression and expansion alone was not enough to produce the cold temperatures necessary to liquefy certain gases. Much colder temperatures were needed.
This lead to the Claude process of gas liquefaction.
It is essentially the same as the Lind process except that in the Claude process the gas is allowed to expend in a cylinder with a piston so that heat is converted to work.
In doing work, the gas loses much more energy than by simple expansion alone. The result is much colder temperatures can be reached, making it possible to liquefy much more difficult to liquefy gases.
https://youtu.be/f7E6N_R1q_4
Notice, the only difference between this and the previous video is the addition of a piston and cylinder for the compressed gas to expand and perform work pushing the piston thus losing energy and growing cold in the process.
The same process is happening in a Stirling engine. The heated and expanding air is first compressed, then allowed to expand and perform work driving the piston.
This is the most effective cooling method known for reaching extremely cold cryogenic temperatures.
The compression and expansion in a Stirling engine, and conversion of heat into work is not on this scale of 100 atmospheres of pressure, but the air in a Stirling engine undergoes the same basic adiabatic cooling process used to reach cryogenic temperatures.
A Stirling engine is going through the same motions as a Stirling cryo-cooler.
It is not impossible, IMO for a Stirling engine to act simultaneously as both a work producing engine and a cooler.
There are various processes used to get air to such cold temperature, one being the Linde process, which involves simple expansion, as in the previous video
https://youtu.be/HmGDnaKZxxU
The air is first compressed, then allowed to expand. Very high compression is used around 100 atmospheres which is far higher than can be reached in a Stirling engine, but the process is the same. A Stirling engine simply alternately compresses air, then allows it to expand.
In the above air liquefaction process it was found that compression and expansion alone was not enough to produce the cold temperatures necessary to liquefy certain gases. Much colder temperatures were needed.
This lead to the Claude process of gas liquefaction.
It is essentially the same as the Lind process except that in the Claude process the gas is allowed to expend in a cylinder with a piston so that heat is converted to work.
In doing work, the gas loses much more energy than by simple expansion alone. The result is much colder temperatures can be reached, making it possible to liquefy much more difficult to liquefy gases.
https://youtu.be/f7E6N_R1q_4
Notice, the only difference between this and the previous video is the addition of a piston and cylinder for the compressed gas to expand and perform work pushing the piston thus losing energy and growing cold in the process.
The same process is happening in a Stirling engine. The heated and expanding air is first compressed, then allowed to expand and perform work driving the piston.
This is the most effective cooling method known for reaching extremely cold cryogenic temperatures.
The compression and expansion in a Stirling engine, and conversion of heat into work is not on this scale of 100 atmospheres of pressure, but the air in a Stirling engine undergoes the same basic adiabatic cooling process used to reach cryogenic temperatures.
A Stirling engine is going through the same motions as a Stirling cryo-cooler.
It is not impossible, IMO for a Stirling engine to act simultaneously as both a work producing engine and a cooler.
Re: Stirling engine and cooler?
Another thing to keep in mind, I think, about Adiabatic expansion and contraction is that a Stirling engine is an Oscillator.
To some extent, the piston can go back and forth or up and down without any flywheel, even without any added heat.
During compression, the heat and pressure build until the piston is pushed out, then energy is stored as momentum, after which the air cools and contracts and the piston is "pulled" back in, or down, and the temperature and pressure builds up again, the piston is pushed back out. If not for loses due to friction, this free oscillation could continue indefinitely.
If a Stirling engine is operating without a load, the only heat that is required to keep it running, then, is just enough to make up for friction loses.
https://youtu.be/vLtU7_AofrM
https://youtu.be/vT6n7VVBvqw
To some extent, the piston can go back and forth or up and down without any flywheel, even without any added heat.
During compression, the heat and pressure build until the piston is pushed out, then energy is stored as momentum, after which the air cools and contracts and the piston is "pulled" back in, or down, and the temperature and pressure builds up again, the piston is pushed back out. If not for loses due to friction, this free oscillation could continue indefinitely.
If a Stirling engine is operating without a load, the only heat that is required to keep it running, then, is just enough to make up for friction loses.
https://youtu.be/vLtU7_AofrM
https://youtu.be/vT6n7VVBvqw
Re: Stirling engine and cooler?
More on the Claude process:
https://chemistry-desk.blogspot.com/201 ... s.html?m=1
Is there any reason why this physics principle should stop working just because the "piston in an engine" is intended for power production rather than air liquefaction?
Yes, the pressure is much lower, so the temperature reduction is less, but how much less?
As noted previously, air liquefies at -318°F
How much cooling then, might be expected from a model LTD engine with a compression ratio of 1:1.2 ?
What actually matters, compression ratio or actual work output? In theory, there could be work output with no real compression whatsoever, where the work output is closely matches with heat input. The gas can expand doing work pushing out the piston with little if any actual rise in internal pressure.
.when a gas expands adiabatically against a piston in an engine, it does some external work, hence its internal energy falls and consequently the temperature of the gas falls
https://chemistry-desk.blogspot.com/201 ... s.html?m=1
Is there any reason why this physics principle should stop working just because the "piston in an engine" is intended for power production rather than air liquefaction?
Yes, the pressure is much lower, so the temperature reduction is less, but how much less?
As noted previously, air liquefies at -318°F
How much cooling then, might be expected from a model LTD engine with a compression ratio of 1:1.2 ?
What actually matters, compression ratio or actual work output? In theory, there could be work output with no real compression whatsoever, where the work output is closely matches with heat input. The gas can expand doing work pushing out the piston with little if any actual rise in internal pressure.