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Well, upon running for some time, these engines appear to achieve a balance as far as heat input and heat utilization and/or output.

Personally I just find it strange the piston returns at all without a flywheel.

Talking about recoil. A bullet does not stop some distance down the barrel of a gun and suddenly reverse course.

The main question is, you said: "in practice you need the heat flow out in order to contract the working fluid."

I'm not so sure, because, in the first place, heat transfer by conduction is a relatively slow process, while comparatively, these engines run very fast. The heat is disappearing instantaneously. So in reality, how much heat is actually flowing out to the sink? I'd say this is quite variable depending on the design of the engine, heat source, etc., but with these laminar flow engines, I would guess it is near zero.

If enough heat is converted into motion, "work", electric current or whatever, to cool the gas enough to cause the piston to suddenly reverse course, who is to say the gas, at that point, is not actually colder than the "sink"?

A similar situation where a piston is driven by an expanding gas in an expansion engine, also converting heat into work, like a Stirling engine, the gas can drop to cryogenic temperature.

The expansion of gas in a Stirling engine does not appear to be significantly different from the expansion of gas in an expansion engine for cryogenic cooling.

Another thing I think happens is on the return stroke the air in the cylinder is compressed, maybe not to the extent that air is compressed in a fire piston, but the principle is the same.

https://youtu.be/-39wmSBO2FM

Tom Booth wrote: ↑Sat Jun 20, 2020 6:03 pm Well, upon running for some time, these engines appear to achieve a balance as far as heat input and heat utilization and/or output.

Personally I just find it strange the piston returns at all without a flywheel.

Talking about recoil. A bullet does not stop some distance down the barrel of a gun and suddenly reverse course.

The main question is, you said: "in practice you need the heat flow out in order to contract the working fluid."

I'm not so sure, because, in the first place, heat transfer by conduction is a relatively slow process, while comparatively, these engines run very fast. The heat is disappearing instantaneously. So in reality, how much heat is actually flowing out to the sink? I'd say this is quite variable depending on the design of the engine, heat source, etc., but with these laminar flow engines, I would guess it is near zero.

If enough heat is converted into motion, "work", electric current or whatever, to cool the gas enough to cause the piston to suddenly reverse course, who is to say the gas, at that point, is not actually colder than the "sink"?

A similar situation where a piston is driven by an expanding gas in an expansion engine, also converting heat into work, like a Stirling engine, the gas can drop to cryogenic temperature.

The expansion of gas in a Stirling engine does not appear to be significantly different from the expansion of gas in an expansion engine for cryogenic cooling.

The bullet is being pushed out with enough force that it's inertia is still far greater than air resistance by the time it exits.
If there were no heat flow out, then you couldn't get any work out of the engine because the piston moving back in compresses the air and heats it back up. If it were still retaining all the heat it got from the burner the pressure would be the same as it was on the down stroke and would require just as much force to push the piston back in with no net force left over to run the engine. Remember that unlike in space, shedding heat in an atmosphere happens mostly by conduction rather than just radiation. The reason heat can't be treated exactly the same as other forms of electromagnetic radiation in this case is because in addition to giving off photons, it also transfers kinetic energy between atoms by them directly bumping into each other.

To reiterate Tesla's argument:

"Heat, though following certain general laws of mechanics, like a fluid, is not such; it is energy which may be converted into other forms of energy as it passes from a high to a low level.... If the process of heat transformation were absolutely perfect, no heat at all would arrive at the low level, since all of it would be converted into other forms of energy"

A few posts back, in response to my paraphrase, or reframing of this argument you said"

ME: "If the heat is transformed into mechanical motion to drive a dynamo to light lights etc. The energy represented by that light, which was originally heat, before it's transformation into light, cannot also travel through the engine to a heat sink.

"Any concept that heat must of necessity flow through a heat engine to a sink, like water through a turbine is entirely wrong IMO."

Your response:

Technically true, but in practice you need the heat flow out in order to contract the working fluid so it can be heated again and expand for the next cycle.

I'm a bit uncertain about your position on this.

Are you actually trying to say that regardless of the heat being converted to electricity or whatever, It still must ALL flow through the engine to the heat sink?

So, heat, in effect, becomes electricity, but the same heat also warms up the sink?

You say "If there were NO heat flow out, ...

And;

" If it were still retaining ALL the heat it got from the burner..."

No one is talking about RETAINING heat. Certainly not retaining ALL the heat.

If I take a lump of clay out of the earth and transform it into a bowl, fire it in an oven, glaze it, use it to eat my cereal each morning, I can't still retain my lump of clay to return to the earth. Same with conservation of energy. I can't use heat to generate electricity and still retain the same heat, to be returned to the sink. Like the bowl, the heat has already been transformed. The transformation of heat does not "retain" heat any more than shaping clay into a bowl retains the original lump.

Heat transformed into "work" is heat leaving the engine AS work. On an atomic level, the heat may still be Kinetic energy, but it is no longer heat, it has become work, the mass movement of the piston, and/or the motion of electrons.

Transformation of heat into work produces cooling as surely as transfer to a sink, but is instantaneous.

"The reason heat can't be treated exactly the same as other forms of electromagnetic radiation in this case is because in addition to giving off photons, it also transfers kinetic energy between atoms by them directly bumping into each other."

I'm not sure what you mean by that. "Kinetic energy between atoms" includes the transfer of kinetic energy between the expanding gas and the piston.

When a "HOT" gas molecule strikes the piston and the piston moves, bumped by the gas, (or millions of gas molecules simultaneously). The gas looses it's kinetic energy, which, in actuality IS it's HEAT.

In driving the piston, the hot expanding gas transfers it's kinetic energy to the piston, so the gas becomes instantly cold at that exact moment. That same heat that has been transformed is not "retained".

Tom Booth wrote: ↑Sun Jun 21, 2020 9:26 am To reiterate Tesla's argument:

"Heat, though following certain general laws of mechanics, like a fluid, is not such; it is energy which may be converted into other forms of energy as it passes from a high to a low level.... If the process of heat transformation were absolutely perfect, no heat at all would arrive at the low level, since all of it would be converted into other forms of energy"

A few posts back, in response to my paraphrase, or reframing of this argument you said"

ME: "If the heat is transformed into mechanical motion to drive a dynamo to light lights etc. The energy represented by that light, which was originally heat, before it's transformation into light, cannot also travel through the engine to a heat sink.

"Any concept that heat must of necessity flow through a heat engine to a sink, like water through a turbine is entirely wrong IMO."

Your response:

Technically true, but in practice you need the heat flow out in order to contract the working fluid so it can be heated again and expand for the next cycle.

I'm a bit uncertain about your position on this.

Are you actually trying to say that regardless of the heat being converted to electricity or whatever, It still must ALL flow through the engine to the heat sink?

So, heat, in effect, becomes electricity, but the same heat also warms up the sink?

You say "If there were NO heat flow out, ...

And;

" If it were still retaining ALL the heat it got from the burner..."

No one is talking about RETAINING heat. Certainly not retaining ALL the heat.

If I take a lump of clay out of the earth and transform it into a bowl, fire it in an oven, glaze it, use it to eat my cereal each morning, I can't still retain my lump of clay to return to the earth. Same with conservation of energy. I can't use heat to generate electricity and still retain the same heat, to be returned to the sink. Like the bowl, the heat has already been transformed. The transformation of heat does not "retain" heat any more than shaping clay into a bowl retains the original lump.

Heat transformed into "work" is heat leaving the engine AS work. On an atomic level, the heat may still be Kinetic energy, but it is no longer heat, it has become work, the mass movement of the piston, and/or the motion of electrons.

Transformation of heat into work produces cooling as surely as transfer to a sink, but is instantaneous.

"The reason heat can't be treated exactly the same as other forms of electromagnetic radiation in this case is because in addition to giving off photons, it also transfers kinetic energy between atoms by them directly bumping into each other."

I'm not sure what you mean by that. "Kinetic energy between atoms" includes the transfer of kinetic energy between the expanding gas and the piston.

When a "HOT" gas molecule strikes the piston and the piston moves, bumped by the gas, (or millions of gas molecules simultaneously). The gas looses it's kinetic energy, which, in actuality IS it's HEAT.

In driving the piston, the hot expanding gas transfers it's kinetic energy to the piston, so the gas becomes instantly cold at that exact moment. That same heat that has been transformed is not "retained".

Yeah, I think we've spent the last few pages misunderstanding each other. I thought you were saying that a lamina flow engine didn't need to shed ANY heat to function.

Right. I think that may be a real possibility.

Carnot thought ALL the heat ("caloric") needed to pass through the engine and out, like water over a waterwheel.

That idea persisted, and in general continues to persist.

It looks to me like all the heat entering into the gas in a laminar flow Stirling is being converted to "work" for the piston to return so rapidly with no flywheel to make it return or force it to return.

It returns 100% of the way, near instantaneously.

Heat can be converted to work instantaneously, resulting in cooling.

Loosing heat (or cooling) by conducting it away to a sink takes time.

I think that if people believe heat must be removed by dumping it to a cold sink, it becomes self fulfilling. Inefficiencies are introduced in engine design which only rob the engine of torque and power.

Personally I think a Stirling engine could produce cold.

That, in fact, is what a Stirling engine does. It takes in heat and converts it into work, producing cold. It is itself a kind of refrigerating device, converting heat into work and producing cold.

The "sink" sets a limit on how much cold can be produced, because below the temperature of the sink, heat will flow in reverse from the sink into the engine.

Lower the temperature of the so-called sink, and the engine can convert that much more heat into work before there is a reversal of flow. But heat does not have to flow to the sink. The sink only sets a limit.

So, if an engine runs "on ice", really it is running on ambient heat. The engine does not transfer heat to the ice. The ice just sets a limit on how much heat the engine can convert to work. Below the temperature of the sink, (in this case ice) the engine will become colder than the ice and heat will begin to enter the engine from the ice, so the engines cold side can become no colder.

But, if the cold sink is well insulated from ambient heat, it may be possible to gradually decrease the temperature of the sink.

So yes, I am saying that in theory, the engine does not, of some necessity, need to "shed" any heat to the sink, not if it is successful at converting all the heat it gains into work.

That was Tesla's proposition. That a heat engine running on cold (ambient heat) would convert, if designed "perfectly" all the heat into work, but even if not entirely perfect, energy gained from the ambient could be used to maintain the sink at the same cold temperature while also producing external work.

It looks to me like a laminar flow Stirling may already be converting all the heat that actually enters the engine and heats up the gas into work 100% (or more) allowing the piston to very rapidly return with no flywheel many times per second. Many times faster than it takes the engine to heat up or cool down by heat conduction.

I see this as evidence that Tesla may have been right.

At any rate, putting an engine on some ice, on a vacuum insulated container to measure how much heat ACTUALLY passes through a Stirling engine and into the ice, under various conditions and circumstances, is an easy, repeatable experiment, that, as far as I know, has never been tried.

As far as I can determine, the second law of thermodynamics is a dogmatic assertion that many have been very reluctant to challenge in any way for 200 years. Hardly anyone even bothers to try. Ultimately it derived from a false assumption, that heat is a fluid.

Tom Booth wrote: ↑Tue Jun 23, 2020 9:17 pmAs far as I can determine, the second law of thermodynamics is a dogmatic assertion that many have been very reluctant to challenge in any way for 200 years. Hardly anyone even bothers to try. Ultimately it derived from a false assumption, that heat is a fluid.

I've never heard anyone say it's actually a fluid, just that using fluid as an analogy is a good way of explaining it to the layman. Just like it's a useful comparison to electricity.

Sockmonkey wrote: ↑Fri Jun 26, 2020 4:51 pm

Tom Booth wrote: ↑Tue Jun 23, 2020 9:17 pmAs far as I can determine, the second law of thermodynamics is a dogmatic assertion that many have been very reluctant to challenge in any way for 200 years. Hardly anyone even bothers to try. Ultimately it derived from a false assumption, that heat is a fluid.

I've never heard anyone say it's actually a fluid, just that using fluid as an analogy is a good way of explaining it to the layman. Just like it's a useful comparison to electricity.

When I say "Ultimately it derived from a false assumption, that heat is a fluid." I was referring to Carnot and the caloric theory. From about 1770 onward for nearly 100 years it was the prevailing theory. Quoting Wikipedia: "Sadi Carnot developed his principle of the Carnot cycle, which still forms the basis of heat engine theory, solely from the caloric viewpoint." https://en.wikipedia.org/wiki/Caloric_theory

The idea that heat is a liquid that flows through an engine like water was taken quite literally. It kind of makes me cringe when people start preaching to me about Carnot efficiency and heat needing to be removed from a heat engine to a sink before more heat can be added.

The operative word here being "STILL": "still forms the basis of heat engine theory".

IF, and I suppose, that is a big "if", Tesla was right, then why wouldn't something like this work?
The exploded view is for illustration purposes, but could, theoretically, work as depicted.

The thing in the middle being a Stirling engine with a hot cylinder and cold cylinder.

I drew this off the top of my head just a minute ago, so it's a bit sloppy.

For better efficiency, possibly this could all be on a single shaft rather than being belt driven

Instead of a reciprocating compressor, a turbine could be used for the compressor.

This would work similar to a bootstrap air cycle heat pump or automotive turbocharger, where the "exhaust" gas helps to lighten the load on the compressor.

In other words, the Stirling engine is not driving the turbo-generator, but rather the turbo-generator is helping drive the compressor.

Another way of looking at it is that the energy needed for compression is partially compensated when the compressed air is released through the turbo-generator.

Compression and expansion of the air produce a temperature difference, which, of course, is used by the Stirling engine.

What heat the Stirling engine uses also reduces the load on the compressor by cooling the compressed air.

The cooled air, when expanded through the turbine, further reduces the temperature of the exhaust, which widens the temperature differential.

Unless you're burning fuel to introduce heat, the fact that no machine is 100% efficient means it wouldn't run. When you compress air to heat it, some of that heat is going to radiate into the environment so it's not going to put that energy into spinning the turbine.

Of course, what you say is absolutely true.

Tesla's counter argument goes something like this;

Suppose we can get this machine started not by heating it, but by cooling the cold cylinder with, let's say - Dry Ice.

To keep the dry ice as cold as possible, we can turn a Dewar (vacuum insulated container) over it.

Now the engine has begun running, technically, not on ice, but on the ambient heat freely available to the hot cylinder directly from the atmosphere.

At that point we begin "adding fuel" by using the Stirling engine to pump in more warm air from the atmosphere.

Immediately, the additional "heat of compression" begins to increase the temperature difference.

The engine, already running on atmospheric heat at ambient temperature, now has some "extra" fule, above and beyond what it needed to get started..

The extra heat adds additional torque..

Next, following the compressed air through the pipe, the compressed air leaves the pipe through a nozzle, in the process, the high velocity air from the nozzle drives a turbine.

The turbine contributes more power to the engine. At the same time the air has been growing cold from loosing heat by conversion to work, first in the Stirling engine and second, in driving the turbine.

Now electrical energy is already leaving "the system" as electricity from the turbo-generator.

How cold is the air leaving the turbine? It may, or may not be as cold or colder or warmer than the dry ice. But maybe that can be ignored for now because if colder, we can use it to keep the dry ice cold, if warmer, it could just be exhausted to atmosphere.

The important thing is how much heat gets through the heat engine and into the "sink"? Does it heat up the dry ice?

We can get an answer to that with a simple experiment.

Run a Stirling engine on regular ice from the refrigerator kept cold with a vacuum insulated container.

If the Stirling engine by itself can remove all, or nearly all the heat so the ice does not melt, or melts very very slowly, what happens with additional cooling from the turbo-expander?

It is not entirely clear to me that the exhaust air necessarily, must be warmer than the ice.

If necessary, it might be possible to cool the compressed air an additional amount with passive evaporative cooling before it exits the nozzle in the turbo-generator, by running the pipe through a water bath.

The second law of thermodynamics says that no matter what we do, we can never come out ahead. The ice will always melt, eventually.

Nevertheless, this second law seems arbitrary to me. Historically, I have not been able to find any record of any actual experiments running heat engines on COLD in such a manner.

Well, I take that back. There are some examples, but they do not seem to prove the case for the thermodynamicist.

https://youtu.be/c-0-zH4Ip7w

With the Stirling engine set up, previously described, this seems equivalent to heating the drinking birds lower bulb and cooling the upper bulb simultaneously.

In other words, the only examples of such "experiments" of heat engines running on cold (or rather, atmospheric heat), are ones like this drinking bird, that appear to actually work.

Or, since we don't really need it to run the engine, suppose we use the excess "heat of compression" to run a Vuilleumier heat pump to keep the ice, or dry ice or whatever cold?

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

Use cold to pump heat to make more cold, as there is already abundant heat in the atmosphere, we don't really need fuel to make more heat. But why should it be "impossible" to use heat to generate cold?

The Stirling engines I originally ordered (from someone on eBay) months ago never arrived, so far anyway.

Impatient with the delays, I reordered the engines from another source/supplier;

https://www.stirlinghobbyshop.com

Which just arrived today, after just a few weeks. So, I can start some experiments, soon.
They appear to be quite well made, with real bearings and things, and not appreciably more expensive than some cheaper models commonly available

The ice will always eventually melt because there is no 100% perfect insulator, and no machine is 100% efficient. There are always mechanical losses.