Isolated cold hole

[Tom Booth]

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So!

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What's the problem?


"But the original question involved an assumed set influx of heat that was being removed by a set size of cooler. Putting an engine in would block and slow down that process, effectively destroying the effort."

Only in your imagination. I think, in reality, or in theory at least, the engine will assist and accelerate the cooling process by removing some heat before reaching the evaporator.

Of course, theories and opinions don't necessarily coincide with experimental outcome.

It would be an interesting experiment.

[Fool]

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VincentG, your latest scenario works like the following. LTD engines are limited by Carnot. Th-Tc/Th. As the object's temperature decreases, Th gets closer to Tc, so Tc must be lowered. More cooling power input just to keep the engine running. You hope to end up with the object at Tc, but that will require a cooler at Tc-∆T. ∆T is required to keep the engine running. Otherwise a very small percentage of ∆Q would even be converted.

Run the numbers to see if your idea has any real benefits. Stirling Engines don't run well with decreasing Th's. In your latest scenario, Th needs to become Tc. That heads to efficiency of zero. In your AC example Th should become 78 F or less. Efficiency of the engine will drop to single digit numbers. Very little help for the trouble and slowing of the desired effect.

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[Fool]

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Tom I whole heartily suggest that you run that experiment. Start with building a Stirling Engine that you are comfortable with to use in such a scenario. Then add the cooler.

Remember it needs to run at very low ∆T, and at high power levels, kilowatts. Good luck. Carry on.

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[Tom Booth]

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Tom I whole heartily suggest that you run that experiment. Start with building a Stirling Engine that you are comfortable with to use in such a scenario. Then add the cooler.

Remember it needs to run at very low ∆T, and at high power levels, kilowatts. Good luck. Carry on.

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Sorry but I've got many other priorities and no particular interest in such redundant experiments.

I don't doubt that heat is converted into work by a Stirling engine, and having a Stirling engine "help" a heat pump cool a room serves little if any practical purpose.

I don't need to prove a point to you or myself when I've already done dozens of similar experiments that have already answered my questions.

It would be a lot of time and money invested for little return in regard to something I already know, and I'm not interested in reducing my air conditioning costs.

I'm interested in eliminating my utility bills altogether.

[VincentG]

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The hot lump of steel inside the freezer may be a better example.

This is a completely different scenario than the opening question. It show why I asked for a block diagram.

Yes outputting work will reduce the heat going into the ice box, making the coolers work less. But it is a one time deal the hot object has a set ∆Q. There is no time constraint on getting that heat out. Even though putting an engine in-between the hot and cold would slow the process down, it would eventually get done, ideally.

But the original question involved an assumed set influx of heat that was being removed by a set size of cooler. Putting an engine in would block and slow down that process, effectively destroying the effort.

Even in the real world, if the goal is to cool off the object in a freezer, putting an engine in-between will certainly slow the effort.

Still, overall the COP of the cooler will not be greater than the Carnot equation.

I don't think it's a different scenario at all, it's really the same exact thing only in the first example the heat is purely ambient. I was not considering a time constraint, only overall energy. So without consideration for time or degrading temperature/efficiency, would less heat energy need to be removed from the freezer with the lump of steel doing work though an engine? Or is it the same overall heat energy but with a lower temperature after being made to do work and sinked to the cold plate/freezer?

The engine in-between the hot and cold may slow the process down(entirely dependent on cycle rate) but it would still allow it. The low efficiency of an LTD would not prohibit a large energy flow. Air conditioners can move millions of Joules with only a relatively small temperature delta between ambient and Tlow.

Even a small percentage of a 50 million Joule(~50,000 BTU) air conditioner is a lot of energy. Increasing the pressure levels of an LTD engine is all that is needed to make low efficiency engines consume large quantities of energy.

[Tom Booth]

"Yes outputting work will reduce the heat going into the ice box, making the coolers work less."

Fool, can I quote you on that?

[Fool]

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No I retract it. There will be no savings. Draw a block diagram.

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[VincentG]

This is a simple proposal and I believe you understand the layout. It seems to have significant consequences regarding the first and second law. It can’t be both ways where efficiency is the measure of percentage of heat converted to work, while at the same time it can’t be accepted that heat is actually converted to work.

[Tom Booth]

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"Yes outputting work will reduce the heat going into the ice box, making the coolers work less."

Fool, can I quote you on that?

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No I retract it. There will be no savings. Draw a block diagram.

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LOL...

Too late, the internet is forever.

[Tom Booth]

This is a simple proposal and I believe you understand the layout. It seems to have significant consequences regarding the first and second law. It can’t be both ways where efficiency is the measure of percentage of heat converted to work, while at the same time it can’t be accepted that heat is actually converted to work.

You would think,

But that is the actual state of thermodynamics today; a world of contradictions. If it were not, I would never have felt any need to do any Stirling heat engine experiments in the first place. And there would be no need for these silly debates.

[Fool]

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You two are welcome to try all you want.

You are trying to cool off the heat source for your engine, by using a cooler and an engine. Good luck with that.

The same goes for the cold sink. You are trying to warm it up with a hot source and an engine. Good luck with that too. Have fun adding extra energy to your cooler.

Engines don't run well with their heat source cooled off, nor their cold sink warmed up.

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[Tom Booth]

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You two are welcome to try all you want.

You are trying to cool off the heat source for your engine, by using a cooler and an engine. Good luck with that.

The cooler would be cooling the engines cold side. It is cooling the engines' sink not the heat source.

The same goes for the cold sink. You are trying to warm it up with a hot source and an engine. Good luck with that too. Have fun adding extra energy to your cooler.

The sink for the cooler is the outdoor environment. You can't really heat up the outdoors by adding a little heat from a building, but anyway, you would be adding less heat with the engine than without.

Engines don't run well with their heat source cooled off, nor their cold sink warmed up.

Again, you don't appear to understand how an air conditioner works, or VincentG's proposed setup.

It would have to be assumed the building gets hot from people (body heat), sun in windows, appliances, lack of adequate insulation etc. so the engine has a continuous supply of heat. The cooler only cools the cold side of the engine(s) not the room or building.

[Fool]

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Again, you don't appear to understand how an air conditioner works, or VincentG's proposed setup.

Again without a magic block diagram, I can only guess what he's thinking. My attempts to draw one leaves too many variables to consider. They all appear to be constrained to the Carnot limit. So I can't help.

The engine cools the room, the hot side. You are cooling the thing the engine needs to be hot.

The engine warms it's cold plate, which warms the cooler's exchanger. Making the engine less efficient.

The heat is exhausted to the outside by being hotter than the outside. Normal cooler function.

Heat into the combined machines, heat out of cooler. Energy into cooler. True of any block diagram. Unless??? Unfortunately, the normal Carnot limit still applies. "Why", will need a block diagram and more, before an analysis can be made, at least.

You need to provide the magic block diagram around that limit.

As I've said, please submit this magic configuration. Since neither of you two have, I assume neither of you two can. That is because, what is proposed is impossible. But, I have hope.

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[Tom Booth]

I posted this in here somewhere about ten years ago:

heat_engine_pump.jpg (137.46 KiB) Viewed 1234 times

Someone else borrowed it:

https://www.physicsforums.com/threads/a ... rk.667129/

[Fool]

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Yep, magical engine running at 70% off ambient temperature. Do you have one of those? More than likely it will struggle to get 10% for a heat pump COP of 3.

Magical COP 3 heat pump running between somewhat wider temperature difference than the engine needs for it's 70% efficiency. Do you have one of those? More than likely it will get a COP of 1.25 or less for a 70% engine goal.

Both will probably be worse than those figures.

I'm not saying it's impossible. Advanced technology is indistinguishable from magic. But, unless you have both of those, you really are talking magic. As I've said, everything I've drawn up is subject to Carnot's Limit. Your's too, apparently.

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