Should ice take longer to melt when used to run a heat engine?

[russ_watters]

I made the styrofoam insulating disk for the purpose of insulating the engines heat sink, in an effort to eliminate the sink, to see if the engine could run without a sink. Or perhaps even run better.

That would be a violation of the second law of thermodynamics.

I thought that since a Stirling engine basically acts as a refrigerating device -taking in heat and transforming it into work, and producing cold in the process, the so-called "sink" might actually be a source of heat which could lessen the efficiency of the engine.

A heat engine and refrigerator are opposite devices. You can't do both at the same time. No; a Stirling engine is not a refrigerator. The purpose of the cold sink for any heat engine is to pull heat away from the engine. The cold sink is colder than the output of the heat engine.

 

[Tom Booth]

A heat engine and refrigerator are opposite devices. You can't do both at the same time.

I disagree with that opinion. My own careful observations over many years studying how Stirling engines work, led me to the conclusion that a Stirling engine in its cycle goes through two phases.

In the first phase heat expands and drives the piston. In the second phase, stored momentum in the piston/crank and flywheel expand the gas, which has already effectively converted it's heat energy to work. This mechanical expansion has a refrigerating effect.

The ambient temperature or "cold reservoir" limits the degree of cooling the engine is able to produce because when ambient temperature is reached by refrigeration, or mechanical expansion of the gas, heat flow reverses, flowing from the "sink", back into the engine.

That is the real reason for the Carnot efficiency limitation. Backward flow of heat from the sink.

 

[russ_watters]

I disagree with that opinion. My own careful observations over many years studying how Stirling engines work, led me to the conclusion that a Stirling engine in its cycle goes through two phases.

Have you looked at a thermodynamics book or online equivalent to see how they describe it? You don't have to try and figure it out yourself -- they are designed and built based on well-known thermodynamics.

 

[Tom Booth]

Have you looked at a thermodynamics book or online equivalent to see how they describe it? You don't have to try and figure it out yourself -- they are designed and built based on well-known thermodynamics.

Sure, I became rather obsessive about studying thermodynamics about ten years ago:

https://stirlingengineforum.com/viewtopic.php?f=1&t=478

 

[Baluncore]

The Mpenba effect isn't real, but even if it were, it wouldn't change the fact that insulation slows heat transfer.

Ah, so that is your problem. You think it is not real, but cannot prove it is not real.
Note; the spelling is Mpemba, NOT Mpenba.

I did not say anything about insulation and the Mpemba effect. That was your straw man, and you have blown it up out of all proportion. I simply said the OP should be aware of the Mpemba effect.
Interesting, I will now consider under what conditions the Mpemba effect might be aggravated by insulation.

You could have just ignored the original reference to the Mpemba effect. Instead you have given it lots of publicity, and you have persisted in derailing this thread from the subject of heat engines.

 

[pbuk]

Why do you think this is true? Or, worse; if there's a working fluid moving, the delta-T can be lower while the heat transfer is larger.

I am attempting to separate the total heat transfer into two components, $Q_w$ which is the heat transferred into the working fluid and $Q_h$ which is the heat transferred into the structure of the engine. All I am saying is that with a greater temperature difference, $Q_h$ will be greater.

It seems to me that you are assuming the fastest heat transfer happens when the engine is shut off and then working the logic from there.

That is the (second hand to me) observation. I am asserting a possible explanation.

What if the entire apparatus were wrapped with perfect insulation? Then the ice would never melt.

And with no temperature differential the engine would never run; I am not sure what your point is here?

It should be possible to melt the ice rapidly by turning on a heat engine. Again: think of an elevated water tank and how fast you can draw energy from it.

I think I would modify this to "it should be possible to melt the ice rapidly by turning on a heat engine and extracting useful work from it". I am trying to get away from analogies as I think the OP may be misled by them - let's stick to the laws of thermodynamics.

However I would imagine that these toy atmospheric heat engines have such a low power output due to the small working fluid volume coupled with the low efficiency due to the small temperature differential that it is very difficult to extract useful work without grinding them to a halt.

 

[sophiecentaur]

Don't get me wrong, I have no criticism of the content of the OP. It was an interesting exercise which, in the light of 'useful' replies from PF, could be repeated and extended to yield some valid answers. I love the idea of home experiments and the toy Stirling is something I would like to get involved in.

But I have to wonder why we are spending so much time and effort on trying to 'explain' / 'justify' the result of an experiment that is, as yet, as full of holes as the one described in the OP. If we were discussing a report from CERN or Fermi Lab and trying to understand an apparently odd result, then the experimental details and the statistics would all be discussed in depth. This time, we have dozens of posts ignoring all that. The numbers are important in this - just as in the search for Higgs Boson.

Forgetting whether or not, the mechanism is a 'heat engine', there is a cylinder of warm air which is moved to a cooled cylinder - and on and on. That will transfer heat to melt the ice (method of mixtures - my school lessons in 1960) . If the machine is not turning then that will not be happening so that particular transfer path will not be there.

In the reported experiment, something is turning the machine and that will increase the rate of heat transfer - all things being equal. That something is explicable in terms of a heat engine. The rest of the experiment is just not explicable in the light of the scarcity of data. I can't find mention of the condition of the room used for the experiments. How about an hourly plot of air temperatures over the day? A ' control' would need to be run at the same time and, of course, the experiment should be run with the control roles being swapped, to reduce the uncertainty.

What are we actually trying to explain here? There is, actually nothing specific that demands an explanation. Heat transfer across one of several different paths with a temperature difference of less than 30C is hard to quantify. We are trying to do the equivalent of explaining the behaviour of a Wheatstone bridge that uses 10MΩ wires, mounted with rusty nails on a water soaked wooden board.

I think the point has already been made that any mechanical energy generated by the Stirling Engine is not going anywhere outside the engine; work against friction is all contributing to melting the ice. Some microwatts of sound may be escaping.

 

[pbuk]

But I have to wonder why we are spending so much time and effort on trying to 'explain' / 'justify' the result of an experiment that is, as yet, as full of holes as the one described in the OP.

From my point of view I have been spending time and effort on this because the OP appears to believe that a heat engine can produce a refrigerating effect without receiving mechanical work input, and that his experiment demonstrates that.

I think it would be a mistake to give the OP the impression that all he has to do is improve the accuracy of his experiment and he will be successful. Instead I hope to show him that this effort would be futile by providing both information about the (well understood and experimentally verified) science of heat engines and a suggestion as to an alternative explanation for the effect that he is seeing.

 

[pbuk]

We are trying to do the equivalent of explaining the behaviour of a Wheatstone bridge that uses 10MΩ wires, mounted with rusty nails on a water soaked wooden board.

I take back what I said about analogies not being useful here

 

[Tom Booth]

I can't find mention of the condition of the room used for the experiments. How about an hourly plot of air temperatures over the day? A ' control' would need to be run at the same time and, of course, the experiment should be run with the control roles being swapped, to reduce the uncertainty.

These are certainly all valid criticisms And as I've mentioned, I do not myself consider any of the observations conclusive of anything.

I ordered six Stirling engine kits, four of the type seen in the video (low temperature differential engines) and two high temperature. in order to run various experiments, with controls running concurrently.

So far I've managed to assemble one of the six kits.

To get some preliminary data and, save some time and get some ballpark, baseline numbers, I decided to do a few informal experiments with the one engine, which I could leave running while I work on assembling the other kits, as well as attending to other responsibilities. My "free time" for playing with Stirling engines is actually very limited.

It would be rather foolish to give any experiments posted on YouTube by amateure experimenters any real weight. For all anyone knows, I've installed a small motor and batteries under all that insulation to keep the engine going under any circumstances.

In other words, I would not believe MYSELF, if I stumbled across these experiments on the internet, conducted by someone else.

I am extremely skeptical by nature myself and am rather disbelieving of my own results, which is why I asked the questions. As an untrained amateure researcher, I don't even know for sure if the results would be considered unusual or expected.

I'm doing these experiments only because I could not find any account of anyone else ever doing them.

I proposed the experiments repeatedly for years and years on many forums, because I did not, and still do not have all the time or resources to conduct proper experiments, but nobody ever thought it would be worth the bother, so I feel compelled to do the experiments myself.

I'm not asking anyone to wast time on it if they consider it a waste of time.

 

[sophiecentaur]

the OP appears to believe that a heat engine can produce a refrigerating effect without receiving mechanical work input,

You are possibly of a generation that never heard of 'Absorption' type refrigerators. There are no moving parts. The energy is supplied by a Heater, there is a hot sink / condenser at the back (as normal) and a refrigerating plate inside. The cycle relies on movement of a kind, in the form of a convection circuit but the driver is Heat. It's very inefficient but it allows you to have refrigeration without an electricity supply. I had one in a camper van and it had three power inputs - gas from the bottle, 12V from the alternator when the engine was running and Mains when you plugged in at a campsite.

The same general principle applies - to obtain a change temperature ' against the flow', something has to get warmer. Actively reducing heat transfer with a form of refrigeration cycle sounds somehow wrong. But I don't see the Stirling as any form of heat pump.

 

[sophiecentaur]

So far I've managed to assemble one of the six kits.

10/10 for effort there - respect!
I have no argument with you or what you're doing - as long as you are looking for valid results and valid explanations. I think the whole thing would be resolved if you do a truly comprehensive and well controlled experiments. Where there appears to be some contradiction of the laws of thermodynamics, it has to be somewhere in the experimental details and, indeed in what you are actually measuring.
There are so many ways in which heat can transfer from hot to cold sink and, slowing down that rate can be due to what I could call 'active insulation' - for instance, where natural convection is resisted with a fan.
One suggestion I could make would be to measure the Heat Input as well as the Output into the ice. Measuring the electrical power needed in a very well insulated hot sink, to keep it at a chosen temperature could take care of the huge unknown about the contribution of the surrounding air in the room. That would supply the other half of the required information in the heat flow equation.

 

[Tom Booth]

You are possibly of a generation that never heard of 'Absorption' type refrigerators. There are no moving parts. The energy is supplied by a Heater, there is a hot sink / condenser at the back (as normal) and a refrigerating plate inside. The cycle relies on movement of a kind, in the form of a convection circuit but the driver is Heat. It's very inefficient but it allows you to have refrigeration without an electricity supply. I had one in a camper van and it had three power inputs - gas from the bottle, 12V from the alternator when the engine was running and Mains when you plugged in at a campsite.

The same general principle applies - to obtain a change temperature ' against the flow', something has to get warmer. Actively reducing heat transfer with a form of refrigeration cycle sounds somehow wrong. But I don't see the Stirling as any form of heat pump.

The Vuilleumier heat pump is quite interesting.

no work is required in an ideal case to operate the cycle. In reality friction and other losses mean that some work is required.

https://en.m.wikipedia.org/wiki/Vuilleumier_cycle

There is a book on the subject "Stirling and Vuilleumier Heat Pumps" but it can be very hard to find these days.

 

[hutchphd]

This is a very interesting post.
I believe that @sophiecentaur has put his finger on the most salient factor: when one draws the ubiquitous heat flow/work extracted diagram, what determines the overall size of the river of heat?? So long as Carnot is not violated, the river can be any size..(.with work or no work). We are used to the constraint being the rate of fuel being input or the size of the cooling fins but there is no reason for that to be the limiting heat flow restriction here.
My knowledge of the Stirling engine is way to sketchy to posit what exactly would generate this behavior. But the fact that it exists (or may exist) is in no way shocking. I think the stopped engine allows a bigger heat flow for some mechanical reason.

I will be interested to know how that works

 

[Tom Booth]

This is a very interesting post.
I believe that @sophiecentaur has put his finger on the most salient factor: when one draws the ubiquitous heat flow/work extracted diagram, what determines the overall size of the river of heat?? So long as Carnot is not violated, the river can be any size..(.with work or no work). We are used to the constraint being the rate of fuel being input or the size of the cooling fins but there is no reason for that to be the limiting heat flow restriction here.
My knowledge of the Stirling engine is way to sketchy to posit what exactly would generate this behavior. But the fact that it exists (or may exist) is in no way shocking. I think the stopped engine allows a bigger heat flow for some mechanical reason.

I will be interested to know how that works

A Stirling engine is, of course, designed to completely block or resist "heat flow" by various mechanical means, Not allowing the heat any passage without performing work.

The mechanisms include the insulating disk (or "displacer") and in some engines a reverse flow heat exchanger (or "regenerator").

But the primary, and often overlooked method of "blocking" heat is the conversion of the heat into other forms of energy by having the heated expanding gas in the engine perform work in driving the piston.

The kinetic energy of the expanding gas is transferred to the piston. The result being that the temperature of the gas, in performing such work diminishes. The heat "disappears" or simply goes out of existence, having been converted or transformed into the mechanical motion of the engine.

In many Stirling engines, the conversion of heat into work is accomplished by channeling the expanding gas through a narrow orifice which creates a high velocity air stream that is directed at the piston.

 

[hutchphd]

Is it possible that absent motion,

The mechanisms include the insulating disk (or "displacer") and in some engines a reverse flow heat exchanger (or "regenerator").

these mechanisms allow more heat flow at "stop" than when the engine is operating at speed? (I'm way out over the edge here so please tell me if this is foolish)

 

[Tom Booth]

Is it possible that absent motion,these mechanisms allow more heat flow at "stop" than when the engine is operating at speed? (I'm way out over the edge here so please tell me if this is foolish)

This (the illustration I'm about to give) is, IMO, wrong in almost every way, but may help conceptualize things

A wind turbine generates electricity at the expense of wind speed, at least for that portion of the wind intercepted by the spinning turbine props.

A stopped Stirling engine is kind of like a wind turbine with the prop tied down. The wind is free to blow through without resistance. If the wind speed behind the prop is measured, there will be a large increase in wind speed when the windmill is sitting idle with the breaks on.

One of the differences with heat engines is that the molecules are not organized into an actual flow, like water in a river or wind. The molecules in a gas are moving in random directions, so the mechanism is not as straightforward as simply intercepting a flow.

But, the principle is similar in that an inoperative machine allows an unimpeded migration, whereas an operational machine is designed to block or intercept it.

 

[sophiecentaur]

The wind is free to blow through without resistance.

Moving air is not the same as high temperature air. The usable energy in wind is mechanical, which is very different from the essentially random motion due to thermal energy. Your attempt at an analogy is not valid, imo.

If you were to try to take this process to a higher power engine, with a source of many kW of heat and a temperature change of hundreds of K, would you expect a similar but more tangible result? The problem with the toy engine is that it produces no useful power. A stirling based electrical generator would be expected to have a large 'unexplained' difference in the temperature of the water in the coolant (or some equivalent measure).

The problem with all this is that your change in rate of melting ice is only one of the measurable variables. Can you be totally sure that a running engine makes no difference to the hot sink temperature? Does it alter the air flow around the apparatus.

You problem is that you are trying (hoping) to show something surprising about regular Science. That puts the onus totally on you to make your experimental method way above reproach and you risk ending up amongst all those other Youtube posters. You have set your bar very high indeed.

I hope you find an explanation. Your investment in money and effort means you deserve a proper outcome.

 

[pbuk]

You are possibly of a generation that never heard of 'Absorption' type refrigerators.

I think you must be confusing me with a younger person - I have also camped with a gas fridge.

But I don't see the Stirling as any form of heat pump.

Any Carnot cycle engine is theoretically capable of operating 'in reverse' as a heat pump. https://en.wikipedia.org/wiki/Cryocooler#Stirling_refrigerators

The reversible nature of the Carnot cycle implies that/is implied by the fact that there is no change in entropy and this makes the process much more simple to deal with both mathematically and conceptually, which I think is quite helpful in this thread.

 

[Tom Booth]

Moving air is not the same as high temperature air. The usable energy in wind is mechanical, which is very different from the essentially random motion due to thermal energy. Your attempt at an analogy is not valid, imo.

If you were to try to take this process to a higher power engine, with a source of many kW of heat and a temperature change of hundreds of K, would you expect a similar but more tangible result? The problem with the toy engine is that it produces no useful power. A stirling based electrical generator would be expected to have a large 'unexplained' difference in the temperature of the water in the coolant (or some equivalent measure).

The problem with all this is that your change in rate of melting ice is only one of the measurable variables. Can you be totally sure that a running engine makes no difference to the hot sink temperature? Does it alter the air flow around the apparatus.

You problem is that you are trying (hoping) to show something surprising about regular Science. That puts the onus totally on you to make your experimental method way above reproach and you risk ending up amongst all those other Youtube posters. You have set your bar very high indeed.

I hope you find an explanation. Your investment in money and effort means you deserve a proper outcome.

I'm not entirely unfamiliar with high power Stirling engines of the type in the desert with giant parabolic mirrors focusing the sun to thousands of degrees.

In fact what set me on this path was a government contractor who wanted my help designing a smaller back yard version for homeowners.

One of the problems these big solar dish utility grid engines have is overheating when the load on the electrical grid drops.

It was in trying to understand the thermodynamics involved in such engines that got me to wondering how the load on a Stirling engines managed to keep it running cool.

These engines needed air conditioners to keep them cool when the load on the grid suddenly fell.

With a heavy load on my car engine it overheats. So at first, this made no sense to me, but a big, high power Stirling engine will overheat if electrical usage on the grid drops for any reason.

It may seem quite strange, but in a sense, the load is, or becomes a kind of heat sink. You night say the load siphons off energy which otherwise builds up, causing the engine to overheat.

You might ask yourself, why with a giant parabolic dish focusing hundreds of sun's on it, doesn't a Stirling engine overheat, as long as it is powering an equivalent load? Why doesn't it need an air conditioner to keep it cool, unless the load is lessened?

These engines out in the desert don't have any water cooling system, not much of any real "sink" to take away all that heat of a thousand suns being driven directly into them.

 

[hutchphd]

You problem is that you are trying (hoping) to show something surprising about regular Science. That puts the onus totally on you to make your experimental method way above reproach and you risk ending up amongst all those other Youtube posters. You have set your bar very high indeed.

I'm not sure that is his true intent. I think the OP is more likely to show off a peculiarity of a stirling engine (or indeed this particular design of stirling engine) than anything else. I have never had such a device in my hands and so I feel a bit in the weeds. Seems he is being very careful about making general claims.
Heat experiments are always time consuming and finicky and then there is always some reason they need to be repeated (endlessly). Good luck!

 

[pbuk]

These engines out in the desert don't have any water cooling system, not much of any real "sink" to take away all that heat of a thousand suns being driven directly into them.

Why do you think that? Here is a document describing one such system, and here is another one eg. describing five systems. In each case there is a description of the cooling system e.g. SAIC Arizona "Heat rejection from the engine is provided by a water/glycol cooling system that uses standard radiators and a cooling fan."

Edit: and some data

• Thermal power into engine 31.63 kW
• Stirling shaft power 12.25 kW
• Thermal power out 18.53 kW

So for every 2 W of useful work we get out of this system we have to dump 3 W of useless heat energy in the desert.

 

[Tom Booth]

10/10 for effort there - respect!
I have no argument with you or what you're doing - as long as you are looking for valid results and valid explanations. I think the whole thing would be resolved if you do a truly comprehensive and well controlled experiments. Where there appears to be some contradiction of the laws of thermodynamics, it has to be somewhere in the experimental details and, indeed in what you are actually measuring.
There are so many ways in which heat can transfer from hot to cold sink and, slowing down that rate can be due to what I could call 'active insulation' - for instance, where natural convection is resisted with a fan.
One suggestion I could make would be to measure the Heat Input as well as the Output into the ice. Measuring the electrical power needed in a very well insulated hot sink, to keep it at a chosen temperature could take care of the huge unknown about the contribution of the surrounding air in the room. That would supply the other half of the required information in the heat flow equation.

Controlling/measuring the heat input and output would certainly be interesting.

Insulating the hot side of the engine with a thermostatically controlled heat source would be largely meaningless, though, without also controlling the outside ambient temperature, or room temperature. Even a vacuum insulation is not perfect.

Right now, I don't even have air conditioning in the house, so I'd need the heat source insulated within a climate controlled room. As the engine, when running cold "sweats" rather profusely, humidity would need to be controlled and recorded, possibly barometric pressure, sun spots, moon phases, astrological influences?

I'm doing this because it is fun and interesting. These engines are inexpensive and there really isn't any other way I would rather be spending my time.

Personally, I consider there to be nothing sacred in this endeavor. Carnot thought heat was literally a fluid. Carnot was wrong. I'm not out to disprove established science, but I have no investment in the second law of thermodynamics either.

 

[Baluncore]

For serious examples of practical engines; built and tested to handle hundreds of HP; at over 1000 RPM; using compressed H₂ or He as the expansion gas; with water cooling; see;
NASA Technical Reports Server (NTRS) 19830022057: Stirling engine design manual, 2nd edn
https://archive.org/details/NASA_NTRS_Archive_19830022057

 

[hutchphd]

Carnot was wrong.

Maybe. Maybe not.
To the extent that relativity tells us hot thing are more massive than cold ones Carnot was in fact correct. It is the caloric.
It serves us ill to criticize thinkers of great thoughts for not being perfect.

 

[Tom Booth]

Why do you think that? Here is a document describing one such system, and here is another one eg. describing five systems. In each case there is a description of the cooling system e.g. SAIC Arizona "Heat rejection from the engine is provided by a water/glycol cooling system that uses standard radiators and a cooling fan."

Edit: and some data

• Thermal power into engine 31.63 kW
• Stirling shaft power 12.25 kW
• Thermal power out 18.53 kW

So for every 2 W of useful work we get out of this system we have to dump 3 W of useless heat energy in the desert.

So, there are systems in some locations that have water cooled engines. I don't claim to know everything about every system. All I know is about 20 years ago my friend, a military government contractor familiar with solar Stirlings at that time said those dish Stirlings they were testing out in the desert were cooled with air conditioners.

It isn't the type of cooling, but when and why the cooling was needed, or when the need for air conditioned cooling was greatest, when the load was reduced.

With a load, the engines ran cooler. That is the only point I was trying to make.

The guy wanted air conditioning on his back yard Stirling dish generators he was planning on building. Or thought it would be necessary, so I looked into it.

The engines run cooler and need less cooling when under a load. If the load is reduced, the engines can overheat.

So I spent several months on the project doing research into all this and stayed up late nights designing Stirling engines, then my friend had a change of plans, so after that it became my own hobby of sorts.

 

[Tom Booth]

Maybe. Maybe not.
To the extent that relativity tells us hot thing are more massive than cold ones Carnot was in fact correct. It is the caloric.
It serves us ill to criticize thinkers of great thoughts for not being perfect.

Wow, so, are you saying you still adhere to the caloric theory of heat?

I don't think it serves us well to cling tenaciously to outmoded conceptions. It makes people refuse to look and observe when there might be something new to learn, or discover a different way of perceiving things.

 

[Tom Booth]

I'm not sure that is his true intent. I think the OP is more likely to show off a peculiarity of a stirling engine (or indeed this particular design of stirling engine) than anything else. I have never had such a device in my hands and so I feel a bit in the weeds. Seems he is being very careful about making general claims.
Heat experiments are always time consuming and finicky and then there is always some reason they need to be repeated (endlessly). Good luck!

Since my motives seem to be in question here, I may as well spell it out in detail, (trying to keep it as brief as possible).

I mentioned my government contractor friend. Well I did complete a tentative engine design.

One of the design goals was reduction in the size of the parabolic dish. ( It had to fit in a back yard and be unobtrusive.) The long and short of it was, I ran hundreds of designs in my head, making modifications and improvements until I had this final version that virtually eliminated the dish entirely. It even worked at night, as it did not run directly on concentrated sunlight that had to strike the engine directly. What I came up with was a kind of open cycle refrigeration system that used air as the refrigerant. I'll skip trying to explain how it worked. I can just say that my friend ran it by his associates in the DOA and next time I spoke with him he told me the verdict. They told him it was impossible. After that he became discouraged and dropped the whole idea.

I continued work on this theoretical engine anyway, for years, and years. Then in the course of my research I happened across an article by Nicola Tesla, published in 1900 that described my engine and the working principles behind it, and why he believed it would work. He even worked on building such an engine, up until his workshop burned down.

One of Tesla's assertions was that an engine running on an artificial cold "sink" would not necessarily quickly dissolve the sink by delivering heat to it, because heat is not a fluid but a form of energy and a heat engine converts heat into other forms of energy. In essence he posited that a heat engine running on an artificial "cold hole" , if very efficient, would take longer than might be expected to fill the hole with heat, and in the process destroy the sink, because heat did not pass directly through the engine, as was, at the time the generally established wisdom. Rather, heat was energy that the engine converted to other forms of energy, so that some percentage of the heat did not end up at the sink.

Naturally, the more efficient the engine at converting heat into some other form of energy, the longer the sink would last and the longer the engine would run.

Of course, Tesla's paper was presumably ignored for the most part. It was a conscious direct assault on the postulates of established science of the time.

Low temperature Stirling engines did not exist back then, but in this experiment, such a little engine serves quite well as a means of testing Tesla's mostly long forgotten ramblings. And also might lessen the sting of having all my hard work designing an IDEAL Stirling heat engine rejected. Perhaps my engine design was not so "impossible" after all.

Anyway, though I have some personal interest in the outcome of these experiments, I've tried very hard to avoid the temptation to put my thumb on the scale, but I can't be absolutely certain I'm not doing something, even unconsciously to skew the results.

Personally, when I did the first experiment, taping insulation over the "sink", I fully expected that the engine would come to a halt almost immediately. Instead it ran like 90 minutes longer than the same engine without insulation over the sink.

I had surmised that IF Tesla's assertions were right, that a heat engine mostly converted heat into motion rather than delivering all the heat to the sink, the engine might actually continue running for a little while. But if my own idea, that these engines actually can not only not deliver heat to the sink, but actually produce some cooling, well then maybe it would run a little better if ambient heat were prevented from reaching the sink.

The video recorded the results.

Does anyone else viewing that video clip see what I see? With insulation covering the sink, did the engine continue running, and at that, did it run just a wee bit faster than it was running without the insulation?

As I said in the beginning, I'd love it if anyone else would repeat these simple experiments, with better controls and unbiased objectivity. More stringent controls, whatever. These engines are pretty inexpensive, I'll even foot the bill and have the engines sent to your door.

So does anyone want to take a stab at explaining why a little Stirling engine running on a cup of hot water appears to run a little better with the sink insulated?

 

[Tom Booth]

One reason I have not been able to run concurrent experiments as yet is the last time I got supplies at the hardware store, they were limited in their supply of nylon bolts.

Today, when I went there again, they had restocked the supply.

The reason for modifying the engines by using nylon bolts, if it isn't already clear, is to reduce heat loss. Since one engine has them, I think the "control(s)" should also have them, as, I'm not testing anything directly related to the bolts, it is just an obvious improvement to the efficiency of these engines.

The nylon bolts are thicker than the steel bolts that came with the engines, so it does involve some drilling out holes, aside from normal assembly.

I can't promise that I won't get carried away and end up making more modifications while I'm at it.

Maybe with some modifications the next engine will run 60 days on the same cup of ice, until the bearings wear out or something. Not likely.

 

[sophiecentaur]

It was in trying to understand the thermodynamics involved in such engines that got me to wondering how the load on a Stirling engines managed to keep it running cool.

The engines run cooler and need less cooling when under a load. If the load is reduced, the engines can overheat.

Stirling Engines are not different in they respect; it applies to all systems in which the Power Input is not regulated in the way IC engines work. Your truck gets hot under load because you are putting more fuel in. Solar heating and Nuclear Power stations suffer from the same problem when the load is removed. Over heating can occur in IC engines when the timing is wrong and the efficiency has been compromised; for the same power output, you have to put your foot down further and the radiator has more waste heat to deal with.

I have always been surprised that Solar Energy systems don't just use shutters to control the Power input when it becomes an embarrassment. However, with a low efficiency engine, there is always the problem of dumping the waste Power - even when operating at maximum load.

 

[sophiecentaur]

Of course, Tesla's paper was presumably ignored for the most part. It was a conscious direct assault on the postulates of established science of the time.

Oh dear. I just read this. Can you really think that, in the last 120 years, no one would have utilised all of Tesla's ideas if they actually had legs? (AC has legs of course. ) What you have written comes under the heading 'Conspiracy Theory' and is consequently of no interest to me, unfortunately. I'm out if this conversation.

 

[Tom Booth]

Oh dear. I just read this. Can you really think that, in the last 120 years, no one would have utilised all of Tesla's ideas if they actually had legs? (AC has legs of course. ) What you have written comes under the heading 'Conspiracy Theory' and is consequently of no interest to me, unfortunately. I'm out if this conversation.

Wow.

I guess your gone, but I'll ask anyway: what do you consider "conspiracy theory" in that statement you quoted?

In his own words, from Tesla's paper:

I was vainly endeavoring to form an idea
of how this might be accomplished, when I
read some statements from Carnot and Lord
Kelvin (then Sir Wilham Thomson) which
meant virtually that it is impossible for an
inanimate mechanism or self-acting machine
to cool a portion of the medium below the
temperature of the surrounding, and operate
by the heat abstracted. These statements
interested me intensely. Evidently a living
being could do this very thing, and since the
experiences of my early life which I have
related had convinced me that a living
being is only an automaton, or, otherwise
stated, a " self-acting engine," I came to
the conclusion that it was possible to con-
struct a machine which would do the same.
As the first step toward this realization I con-
ceived the following mechanism...

I think it is quite plain and obvious to anyone with any background or reading on thermodynamics that Tesla is diving headlong into a refutation of what is known today as The second law of thermodynamics.

He goes on to elaborate in detail, why Carnot's and Lord Kelvin's postulates do not hold under all circumstances.

One of those circumstances he elaborates on at length is when a heat engine runs on a manufactured "cold hole".

Reading his paper, I realized Tesla's assertion could be easily disproven experimentally. What he was basically talking about, in modern terms, would be a Stirling engine running on ice. Anyone should be able to easily find half a dozen or more examples on YouTube of Stirling engines doing just that.

But does a Stirling engine running on ice actually have the ramifications Tesla elaborated on? Would it bring down Lord Kelvin's and Carnot's postulate like a house of cards?

Not likely. But that certainly was his intent wasn't it?

So, has Tesla's logical demolition of the second law been universally embraced by all?

I don't see that it has, or I certainly would not be wasting time and money on these experiments.

 

[Tom Booth]

Another consequence of Tesla's rambling, or, let's call it a factor or element of his proposition would be that a heat engine would have to be able to run without passing much if any heat from source to sink.

Again, that Tesla's idea is demonstrably impossible and rediculus on its face can easily be proven by simply insulating the cold side of the engine or "sink" and watch the engine immediately grind to a halt.

I did the experiment and posted here the video of the result.

Well,...?

I assumed the engine with the sink insulated would quickly run down and stop without an outlet for the heat to pass through.

Annoyingly, that did not happen. What did I do wrong? Why did the engine continue running? I poured scalding hot water from the tea kettle into a $5 Dewar flask (of sorts) and put a less than $30 model Stirling engine on top, (insulated so the heat could not leave the engine through the "sink". Or presumably not much) This TOY is not any 100% efficient engine, I thought it should have stopped running, easily demonstrating the fallasy of Tesla's plan.

Before placing the insulation on top the top plate of the engine it felt relatively cool considering there was scalding hot water under it. It felt,.. about room temperature.

With the insulation on top? How hot (or cold?) Did it get?

I don't know. I neglected to put a temperature probe in there, but from the response of the engine, it seemed to run slightly faster. I do know it ran about an hour longer than it ran on hot water previously, without the insulation on top.

I'm not claiming any violation of thermodynamics. I just ran the experiment,
in a mostly skeptical frame of mind as I could not find any record anywhere of any such experiment ever having been conducted before.

If there were some such record of any such previous experiment I certainly would not have bothered with it.

 

[Tom Booth]

Just to be clear what experiment I'm referring to:



This engine is running on hot water poured from a boiling tea kettle. The cup is vacuum insulated.

I had a friend with a stop watch (phone app) help me time the RPM of the engine at the beginning of the experiment, (before the "sink" was covered with insulation) Vs. the RPM towards the end of the video, (after the sink was insulated, with the insulation taped tightly down, with no apparent leaks that I could see)

RPM without sink insulation: 162
RPM with the sink insulated: 180

That is an increase in RPM of about 18 revolutions per minute, give or take a revolution or two, but I think that is a fairly accurate count.

Anyone, please feel free to check that

 

[Vanadium 50]

A machine that violates the second law of thermodynamics is a perpetual motion machine. I understand why you don't want to use those words, but that doesn't change what it is.

1. The number of backyard inventors who think they have built such a thing is large.
2. The number who have actually done so is zero,
3. The fraction who invoke Tesla is also large. But that does not invalidate point 2.

 

[Tom Booth]

A machine that violates the second law of thermodynamics is a perpetual motion machine. I understand why you don't want to use those words, but that doesn't change what it is.

1. The number of backyard inventors who think they have built such a thing is large.
2. The number who have actually done so is zero,
3. The fraction who invoke Tesla is also large. But that does not invalidate point 2.

Well it clearly wasn't a perpetual motion machine. It stopped when the water cooled down after about three hours.

I never claimed it violated any laws of thermodynamics. I honestly don't think it does.

As I said, I just ran the experiment.

Other than replacing the metal bolts holding the engine together it is a stock engine. Assembled according to the directions.

I didn't build anything, I just assembled a $37 kit, like anyone could. And ran a simple experiment.

https://www.stirlinghobbyshop.com/e...irling-engine-ja-828/#cc-m-product-9759217783

 

[Baluncore]

Of course, Tesla's paper was presumably ignored for the most part. It was a conscious direct assault on the postulates of established science of the time.

Nikola Tesla got some things right and much very wrong. Since then he has been misrepresented by conspiracy theorists who don't understand science. Avoid mention of Tesla unless it is essential, or you will be associated with conspiracy theorists.
https://en.wikipedia.org/wiki/Nikola_Tesla#On_experimental_and_theoretical_physics

 

[russ_watters]

Well it clearly wasn't a perpetual motion machine. It stopped when the water cooled down after about three hours.

I never claimed it violated any laws of thermodynamics. I honestly don't think it does.

As I said, I just ran the experiment.

What you believe isn't very clear to me because several of your posts do seem to be advocating Tesla's view that it is possible to create a cold sink while extracting work at the same time. But PF does not discuss perpetual motion machines even for the purpose of debunking them, so either way, unfortunately this thread will need to be closed. It's a shame because I'm a big fan of people doing their own experiments and I commend you for the effort you put into it.

Postscript/summary; I think the group basically reached a consensus that the outcome of the experiment is more based on "flaws" in the machine than general thermodynamic principles. E.G., it can't be said that in general a stopped turbine/engine will pass energy slower or faster than a running unloaded one or a running loaded one. Different machines and setups can produce different results. But those results will always be consistent with the laws of thermodynamics, so one should never conclude that what they are seeing contradicts the laws of thermodynamics, but instead should interpret the results from within that existing framework.