Stirling engine and cooler?

[Tom Booth]

As a couple practical examples of my previous assertion:

Heat enters the engine and is either utilized or returned to the hot side or regenerator.

https://youtu.be/pVZVnxrcosc?t=912

According to the information in this video, (@ 15:15 on, relating to data center cooling) there is a very real practical problem with using Stirling engines to cool data centers A Stirling engine operates by RETAINING heat.

This can also be seen in the infrared imagery.

Two cups of hot water. One with an operating Stirling engine, and one with an inoperative dummy engine.

I think it can be clearly seen from the infrared imagery that the running engine acts to retain heat The top of the engine remains cold while the cup of hot water stays hot, compared with the dummy.

stirling2.png (172.15 KiB) Viewed 5796 times

https://concord.org/blog/an-infrared-in ... ng-engine/

This seems quite contrary to the prevailing "scientific" view that a Stirling type heat engine somehow operates by the heat passing through it to the sink, or "lower level" like a water wheel.

[MikeB]

I quite agree that that video is surprising, but too much so. The exact nature of heat transfer processes & sequences within the engine are certainly complex, but every motor in existence works by converting one form of energy into another, so any suggestion that running a stirling on top of a cup of tea could somehow keep that cup warmer than a dummy has clearly got something spectacularly wrong.

This looks at first glance like a good side-by-side comparison, but it isn't.

[Tom Booth]

I quite agree that that video is surprising, but too much so. The exact nature of heat transfer processes & sequences within the engine are certainly complex, but every motor in existence works by converting one form of energy into another, so any suggestion that running a stirling on top of a cup of tea could somehow keep that cup warmer than a dummy has clearly got something spectacularly wrong.

This looks at first glance like a good side-by-side comparison, but it isn't.

Needless to say, I completely disagree. When it comes to a discrepancy between theory or belief and experimental results, it is more likely that there is something "spectacularly wrong" with our preconceived assumptions.

I agree that at first glance, it makes no sense that a heat engine should reduce the heat loss from the heat source it is running on, but my own experiments would seem to confirm this.

Running on ice, for example, my experiments demonstrated that the ice remains frozen longer when it is used to run a Stirling engine.

https://youtu.be/dQVRVL1OUBg

This engine ran for 33 hours on a cup of ice. With a non-running identical engine under the same conditions the ice melted completely in just 28 hours.

https://youtu.be/NLog-G4XRU0

The experiment was repeated several times using single ice cubes to reduce the time involved with similar results.

I'm not jumping to any conclusions but I'm not just dismissing fairly clear experimental results off-hand either.

Some long held assumptions about how Stirling engines work, could be in error.

[Nobody]

To Tom Booth: You've done some experiments, studies, and come to several conclusions, or perhaps questions. I can't answer them all at once, so please be patient with me. I am trying to help you and understand this better myself.

First answering the opening post. No a Stirling engine can't cool the cold side at the same time it is running. If an engine is driven, in the same direction as it drives, the hot side will cool, as demonstrated in the Philip's video.

There are four functions mentioned in the video:
1. Heat engine running forward, hot head, head cooling
2. Heat pump driven backwards, heating head, until hot.

3. Cold pump, refrigerator, driven forwards, cooling head, until cold.
4. Cold engine running backwards, cold head. Head warming.

In other words, to heat the head it needs to be driven the opposite of how it drives.
To cool the head it also needs to go the opposite way of work direction.

This all says nothing of the base where the base is kept close to the water bath temperature. The opposing thermal sink.

[Nobody]

1 and 3, from above, rotating forward, will both tend to cool the head and warm the water bath base.

2 and 4, from above, rotating backwards, will both tend to heat the head and cool the water bath base.

Just straight answers to the opening post from an accepted thermodynamic viewpoint, and the Phillip's video you provided.

[Nobody]

Your comment that you think, more is going on than the engine pumping heat through it, I tend to agree. It is a little bit like saying infinity is a really big number. Although that is acceptable for a child or even a beginning math student, we both know infinity isn't technically a number. It's more a direction.

Stirling Engines rely on a cycle. That means they go through several processes or states before returning to the original state.

Ideal Stirling:
Compressed cold fluid. Initial state.
1. Displacer moves, regenerator reheats fluid, now highest pressure and temperature. Work needed.
2. Piston moves, fluid expands, hot sink supply's heat to keep fluid temp constant. Work comes out.
3. Displacer moves back to original position, regenerator absorbs heat. Fluid now at lowest pressure and temperature. Work absorbed.
4. Piston moves back to original position, fluid compresses, cold sink absorbs heat keeping fluid at constant temperature. Now it is compressed cold fluid. Work absorbed.

After number four is completed, the system is back to its original conditions, or state, and ready for the next cycle.

That is also a simplification and comes from a standard engineering viewpoint. A real world engine would have a rounded pressure-volume diagram and the above goes away and is replaced by integrating the collected numbers to find out where work and heat go. Not easy. Not needed in this forum.

There is no reason that the cold sink can't be very cold, ice, and the hot sink can't be just warm, room air/water. If the two are exchanged the engine runs backwards but the direction of the cycles is the same.

Note: The working fluid never quite heats to the temperature of the hot sink, and doesn't quite cool to the temperature of the cold sink. The two sinks can keep the temperatures constant under ideal steady state running conditions. Not that they ever do in a real world engine.

[Nobody]

I've discarded any conclusions from the four thermal images. The dummy engine appears not to be an engine at all. What I see is there is something on the left mug that is a better conductor than what appears to be an engine on the cooler right mug. Not even sure what that means. It does heat up some in the progression of photos, a little. No conclusions can be drawn from them. The questions you ask might be simple enough to answer by the thought that the material you placed on top conducts better than you'd hoped and better than the engine running or not.

It also might be answered by, a running engine is cooler than a stopped engine. This seems counter, but possibly explainable. The displacer/regenerator combination allows heat to be stored, and is built to be a good insulator as well as storage device. Heat is delivered to the cold side at a greatly reduced temperature, only slightly warmer than it. It only needs to absorb the heat of compression. The displacer and regenerator also absorb some of this. The hot side is cooled by the expansion and work output process. The engine puts out very little work. This might be because the conduction into, and out of, are very slow.

A stopped displacer may allow a natural convection to flow, resulting in greater heat conduction.

One more thing, the air inside may be going below atmospheric, rendering it a better insulater than the room. A stopped engine will be at normal atmospheric pressure.

None of that is outside the known science of thermodynamics and heat transfer.

[Nobody]

Your experiments with insulating the top of a Stirling and the result of it running better are interesting to me. I love a mystery. It is too early in your testing to draw any conclusions. If you do, you might end up like the ill fated cold fusion men. Think antidotal evidence. Yours needs to be submitted for peer review and replication by others. Improved and different tests are required. You are jumping the gun by publishing it, and in other forums.

In heat transfer I heard a term called critical insulation thickness. It applied to the insulation on electrical wires. It is the thickness of insulation that gives the best heat removal from a wire. Thicker or thinner and less heat escapes. This is a surface area verses thickness equation.

I'm wondering if instead of blocking heat transfer your material has increased it. All materials have the following properties, they are insulators, conductors, and heat absorbers (called heat capacity). Your choice of material may be the fault. Or your testing procedures. Think not how all of thermodynamics is wrong, instead think what am I missing.

The current laws of thermodynamics has allowed engineers to build all kinds of engines, coolers, and many other marvels, including very successful Stirling Engines. Thanks for the video from Philip's. To see a piece of very simple heat pump machinery operate between 700 C, and -196 C just by reversing the direction, plus be able to be a bidirectional motor is nothing short of incredible. Phillip's theories are well backed up. Yours seem to contradict them. To prove your theories you'll need to predict something testable and build it. Incomplete testing and guessing just won't sell.

Please keep up your enthusiasm. That looks good.

If science were easy the pointy end of an airplane wing would go first.

[Tom Booth]

To Tom Booth: ...

First answering the opening post. No a Stirling engine can't cool the cold side at the same time it is running.

I believe it does, or rather CAN, sometimes. Or all the time to one degree or another.

There are dozens of possible variables involved, regenerator, no regenerator. Load, no load. Compression ratio, type of engine, (alpha, beta, gamma, free piston, ltd, thermal Lag, laminar flow, etc.) load balancing, stroke length, flywheel, no flywheel, dead air space, dwell etc. etc.

By definition, a heat engine converts heat to work. In that process it effects refrigeration. Heat disappears or is lost and mechanical work is created in its place.

There is no question that a Vuilleumier heat pump takes heat in at one end and acts as a cooler at the other. A heat driven heat pump, remarkably similar in principle and operation to a Stirling engine.

Generalizations are rather meaningless.

Some Stirling type heat engines appear, under certain circumstances, to effect a cooling of what would normally be considered the cold "sink".

[Tom Booth]

Take a Stirling engine like this that utilizes some form of "cooling fins" between the heat input side and piston cylinder:

https://youtu.be/V4YEhxIRBwY

This helps to prevent heat from migrating to the piston cylinder, which we want to keep cool presumably, by dissipating "excess heat".

But why do we want to "throw away" heat in a heat engine? Heat is what keeps the engine running. It is the actual "fuel" or power source. Is this common practice really helpful or efficient?

Such engine designs, I think, ultimately go back to the Carnot theory that heat MUST be "WASTED" or Let out, just like water over a water powered mill wheel. The same heat that powers the engine MUST pass through to the sink and out the other side or the engine cannot operate, so the theory goes, and people have been adhering to this theory for over a century.

Suppose, however, it is not true?

I agree a temperature difference is needed for a Stirling engine to operate, but are cooling fins really the best way to keep the hot and cold sides separated? Does the heat really need to be wasted, needlessly dissipated? This seems very odd to me, like imagining that it is helpful to the operation of a gasoline engine to drill holes in the gas tank to let out excess fuel.

Aluminum is an excellent conductor of heat. So, how useful, really, is it to put a heat conductor between the heat input side and the cylinder that needs to stay cool?

Well, the aluminum is also good at displaying heat to the air. Seems extraordinarily wasteful of "fuel" to me.

I think, if it is, by chance, NOT NECESSARY to throw heat off to a sink, maybe using some non-heat conducting barrier would be more effective and utilize the heat more efficiently. Bakelite perhaps? Some type of ceramic? Wood? It seems almost anything would be a better heat barrier than aluminum, which is a fantastic heat conductor.

This is just one example of where I think that maybe an obsolete theory of heat has led to a poor, inefficient engine design.

If it is true that a "thermo-acoustic" type Stirling such as this relies heavily on adiabatic expansion, and is therefore "self cooling" what is needed between the hot and cold sides or ends is not a conductor, like aluminum to dissipate heat, but an insulator like bakelite.

Such a heat insulator in place of these aluminum heat conducting "cooling fins" could prevent heat from migrating to the cold cylinder, preserving the temperature differential while also conserving "fuel".

Just maybe.

Theory is one thing, but this should not be too difficult to test.

Apparently Bakelite can be turned on a lathe.

https://youtu.be/dqc5fcyaI20

[Tom Booth]

Your experiments with insulating the top of a Stirling and the result of it running better are interesting to me. I love a mystery. It is too early in your testing to draw any conclusions. If you do, you might end up like the ill fated cold fusion men. Think antidotal evidence. Yours needs to be submitted for peer review and replication by others. Improved and different tests are required. You are jumping the gun by publishing it, and in other forums.
...

LOL

This is "peer review" as far as I'm concerned.

You make some good points.

About the infrared images, like you, I questioned what exactly was used as a dummy engine, so ran some experiments of my own, with similar results. Unfortunately, I don't have an infrared camera handy.

Quite true, replication and variation of experiments would be great, but so far, as far as I know, nobody takes it seriously enough to consider it worth the bother, "everybody knows".

Even me. Even after several experiments, I'm skeptical and probably don't give it enough time and attention. Experiments take A LOT of time, I've found out, and considerable investment in things like infrared cameras.

Like you, I'm just curious. I'm not out to prove anything.

The first time I insulated the sink on a Stirling engine, I anticipated that the engine would quickly overheat and quit running. The last thing I expected was that it would run better and faster, though, I had worked out theoretically that that COULD happen, I was certain my crazy theory had to be wrong.

Contrary to my expectations, the engine ran much better with the sink insulated.

Perhaps the 'insulation" is just a good conductor. I tried three different kinds,; foil backed styrofoam, blue styrofoam, and Corning house insulation. Not a very good endorsement of the household insulation industry if such common house insulating materials actually cause heat loss at a faster rate.

[Nobody]

Insulating a house doesn't increase outside surface area, and it blocks or slows air infiltration.

And, as you pointed out, stops the natural convection that can appear inside the dead air spaces.

[Tom Booth]

(...).

First answering the opening post. No a Stirling engine can't cool the cold side at the same time it is running. If an engine is driven, in the same direction as it drives, the hot side will cool, as demonstrated in the Philip's video.

There are four functions mentioned in the video:
1. Heat engine running forward, hot head, head cooling
2. Heat pump driven backwards, heating head, until hot.

3. Cold pump, refrigerator, driven forwards, cooling head, until cold.
4. Cold engine running backwards, cold head. Head warming.

In other words, to heat the head it needs to be driven the opposite of how it drives.
To cool the head it also needs to go the opposite way of work direction.

This all says nothing of the base where the base is kept close to the water bath temperature. The opposing thermal sink.

I'm not suggesting that the heat/energy flow is being reversed in order to cool the sink.

There is the hot side of the engine and the cold side between which, in an LTD type engine, the displacer moves back and forth.

Simultaneously the piston is responding and the internal pressure and temperature are fluctuating.

There is one other thing happening that frequently escapes many peoples attention. Heat as "kinetic energy" is being transfered from the gas molecules to the piston.

Let's assume some actual load on the engine, somewhere for this "converted" heat into "work" to go -> outside the "system" under consideration.

What it looks like to me is that the piston is like a baseball. There are two batters knocking the ball back and forth between each other. There is some mechanism attached to the ball that serves to extracted mechanical work from the ball/piston.

One "batter" is atmospheric pressure knocking the ball in one direction, the other is heat input knocking the ball back in the opposite direction.

You could say one batter is much stronger than the other but both are contributing some energy to this "system" to keep the ball in motion and to keep generating the kinetic work output.

In other words, Both sides of the engine are experiencing cooling, or transfer of heat into the system as heat and out of the system as work.

The role of the displacer, if it is used, is not to assist the transport of heat through the engine. Rather, it helps to balance and regulate the internal temperature and pressure (and work output) in such a way that energy is always moving in the direction high pressure -> driving piston -> work output.

The displacer introduces heat which "bats" the piston one way, then as the gas expands and drives the piston and the gas undergoes adiabatic cooling, converting the added heat into work output, the displacer "cuts off" heat input, allowing the temperature of the gas to continue cooling by adiabatic expansion as the piston continues traveling outward due to stored momentum, in the piston itself and flywheel, if used.

Atmospheric pressure then "bats" the piston back in the other direction and, in the case where a magnetic "free piston" and linear alternator are used, (or even where it is not used) additional heat to work (mechanical and/or electrical) conversation takes place.

If, but only if, TOO MUCH HEAT is introduced, the "excess" might need to be dumped, the engine overheating, but this can be resolved by load balancing Heat input regulated so as to match work output, and to compensate for loses due to friction.

The lingering idea, stemming all the way back to Carnot and company, that heat MUST be transfered to the cold sink is IMO erroneous.

Yes, it often happens that excess heat is supplied. Stirling engines are very frugal and this is all too easy.

I posted this diagram earlier to help illustrate what I believe actually takes place inside a Stirling engine, or can take place, where there is well regulated load balancing. (Or good load balancing just by "coincidence" or design)

Stirling_engine-cooler_by_Tom_Booth_CC.png (55.61 KiB) Viewed 5563 times

This is not a proposal for some NEW kind of Stirling engine. Just my own insight into how a Stirling engine actually functions already, or should function

Knowing this, it may be possible to make certain modifications or changes to optimize what is already a reality, but if it is considered that these heat engines work by throwing away heat into the sink, efforts to improve Stirling engine performance to compete with IC engines is not likely to succeed.

It is only by having a clear understanding of what is going on in these engines that some improvements might be made, or otherwise it might happen only by some fluke or accident.

I really think heat energy conversion could be on a par with other types of energy conversion, like electricity to heat, or electric motors which can be 85% to 90+% energy efficient.

But we need to stop designing engines based on the assumption that having excess heat and then throwing that excess away is somehow essential.

[Nobody]

Another experiment idea.

Insulate the top plate of your LTDSE as you have been doing. Get it running on top of a cup of hot water in the insulated mug. Move the running engine and the cup into a hot box. I would say oven but am concerned that it would be too hot from an inherent thermostat error. Maybe use an oven thermometer. Set the hot box to the hot water temperature.

The engine should tend to cool the water, and warm the top plate. May have to reduce the hot box temperature as this happens.

If there are any unexpected results, it would be another curious mystery we could investigate. It should stop running fairly quickly.

The most mysterious would have to happen when the oven is the same temperature as the hot water. Different temperatures would also present valid experiments. I'm concerned that your experiments maybe suffering from ambient heat flow. The only way to stop that would be to make ambient the same as the opposing sink, after getting the engine running and insulating the ambient sink, then by putting it in an oven or cooler.

In other words, are you testing Carnot, an engine, or just insulation?

Im curious of your education, are you educated in integral calculus? Do you understand what an integral is? What is it? I will come back with an answer.later. Simple/general answer please. I can explain calculus briefly if there is some interest here. I would start a new thread for it. Thanks.

[Tom Booth]

Another experiment idea.

...

The engine should tend to cool the water, and warm the top plate. ... It should stop running fairly quickly.

... an integral is? What is it?

For all practical purposes, the ambient atmospheric heat is already an "oven", relatively speaking. Or alternatively, if heat is added to the engine, the ice box.

https://youtu.be/BHRWArTFgTs


Either way, it is all the same experiment. You have a temperature differential the engine is operating between.

If, as you say:"The engine should tend to cool the water (hot side - example; boiling water), and warm the top plate (cold side - example; ambient sink, ice or whatever).

Then, again, as you point out: "It should stop running fairly quickly." (If either the source or "sink" are finite / limited, such as a cup of hot water or ice cube).

That is, IF the engine is cooling the hot side and warming the cold side, or put another way, transporting heat from the heat source to the sink.

If, however, the engine is taking in heat, from whatever source and converting that heat into mechanical work output, then the heat is being diverted away from the sink by the engine, rather than being transported to the sink. In that case, the engine should continue running longer, all other conditions being the same.

Due to the first law of thermodynamics; (conservation of energy), the heat cannot be both converted to mechanical work output and simultaneously transported to the sink. Likewise it cannot both be transported to the sink AND converted into mechanical work output, regardless of what might be used as source and "sink".

I put "sink" in quotes as that is the terminology generally used to designate the cold side of a heat engine. If the engine, however, is actually diverting heat away from the cold side by converting that heat to mechanical work output, then the so-called "sink" is not actually acting to absorb the heat. So in that case "heat sink" is a misnomer.