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I'm an engineer, not a forensic nitpicker. I do practical calcs good enough to get the job done, and don't bother about negligible additional forces. That's because nothing ever lives up to its theoretical promise anyway.

If you want to know how many millimetres or extra pascals the gas compressed when the piston was placed on it, ask someone else. ;)

Sorry to hear that. As an engineer, you likely deal with scaling all the time. This is just a peanut size example.

I was able to set 5 pounds of steel into oscillation with just a 40 degree Fahrenheit temperature difference and my 15cc epoxy displacer chamber.

The only limit to this weight, even at incredibly low temperature delta, is the pressure capacity of the chamber and the heat transfer rate of the aluminum plates, which as it turns out is astronomical in relation to practical gas volume.

VincentG wrote: ↑Mon May 20, 2024 12:26 pm Sorry to hear that. As an engineer, you likely deal with scaling all the time. This is just a peanut size example.

I was able to set 5 pounds of steel into oscillation with just a 40 degree Fahrenheit temperature difference and my 15cc epoxy displacer chamber.

The only limit to this weight, even at incredibly low temperature delta, is the pressure capacity of the chamber and the heat transfer rate of the aluminum plates, which as it turns out is astronomical in relation to practical gas volume.

I don't know whether you saw the rest of my reply, answering your original question, as I edited it in a minute or two later.

Which leads back to my original question of how to prove that heat is destroyed when work is done.

Heat isn't a substance, it's manifested as a flow of energy from a hotter body to a colder body.
Energy is neither created nor destroyed, but it can get translated from one thing to another. In our example, the extra Joule started out as additional energy passed from the external energy source into the gas, and ended up as one Joule's worth of gravitational potential energy stored in the piston. So the extra Joule didn't make the gas any hotter, because bits of it were getting stored in the piston as GPE as it rose.

So far as your oscillating chunk of steel goes, I need to get a sense of the scale of this new example you've moved onto. You could tell me more about what the rate of energy input is, what the amplitude of the oscillations are, and whether any springs are involved. It sounds like a pretty exciting experiment anyway!

I thought I had filmed the heavy steel block but I did not. It moved just the same as the copper bar.

https://youtube.com/shorts/WPtcVRK35nU? ... 3tzGUxqpzn

If moving from the copper bar to the 5lb steel block made no noticeable difference to the compression of the gas, you can probably understand why I thought the compression caused by the 102g piston wasn't worth calculating out.

But I'm interested to know what you think about my response to your 'destruction of heat' question.

Moving to the 5lb weight makes a tremendous systemic difference when the starting pressure rises 4psi from 4 extra pounds across one square inch of piston surface.

I'll think about your response until tonight.

Great. Have a good evening.

VincentG wrote: ↑Mon May 20, 2024 11:55 am If the starting pressure at 300k and 100cc was 1atm + the added pressure of the 102g piston, it would be a basic pv=nrt calc.

But if the temperature of 100cc at 300k and just 14.7psi is doubled to 600k, any additional weight will no longer allow expansion to 200cc. The only way to continue expansion to 200cc with the load of the 102g piston would be to increase gas temperature beyond 600k.

That is no longer a case of just adding "Joules". Yes, Joules must be added, but Tmax needs to rise above 600k, rendering the exercise invalid from the start.

Which leads back to my original question of how to prove that heat is destroyed when work is done.

I'm not sure what you two are discussing, so I might be off base here.

If one Joule is added to rase a mass 1 meter and the temperature of the gas remains at 600 K, the volume must change proportionally.

Heat can't be destroyed. It is a quantity of energy transfered from one body containing internal energy measured by temperature to another body containing internal energy at a lower temperature. Internal energy reduces as energy leaves one body and is absorbed by another body. That is called thermal energy transfer. There is no "heat" to destroy.

Internal energy manifests itself in a volume of gas by T•Cv•M.

Engines run by increasing and decreasing internal energy by flow in and out of heat. If less heat flows out than flows in, the engine can do positive work, or store energy. It is misleading to think of heat as a substance. There is no magic quantity of transferring heat. Like there is no magic quantity of transferring work.

Adiabatic processes flow zero heat. As the heat flows it becomes internal energy. Starts as internal energy moves into and staying as internal energy, potentially internal energy is output as work through P•∆V.

A bicycle pump will demonstrate force times distance converted into temperature rise, internal energy rise, and heat transferred from the internal hot air to the cold pump body. That temperature rise and heat loss is detrimental to pumping up a tire. Known also as irreversible entropy gain.

I used to think heat was hot, but that is wrong, colloquial. Hot is internal energy. Heat is just how the energy got there. And something must be hotter to make something else hotter but never as hot. At the same note heat from a hot flame can be added to a large mass, such as an anvil with negligible temperature rise of the anvil, if the duration is short enough. The same with gas in an engine, if there is a matching expansion.

Ahhhh.... Stroller beat me to it. LOL

Regarding the copper verses steel block, I assume it is a weight difference. Just remember moving the displacer up and down is a temperature difference. Although both would move, I would think there would be a difference. I don't know how much. Pressure would be constant for both, but higher for the heavier weight, density would be greater too, and volume smaller. I'll have to look at the video later.

Regarding the copper verses steel block, I assume it is a weight difference. Just remember moving the displacer up and down is a temperature difference. Although both would move, I would think there would be a difference. I don't know how much. Pressure would be constant for both, but higher for the heavier weight, density would be greater too, and volume smaller. I'll have to look at the video later.
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The copper bar weighs one pound. The volume was the same, since I can set the starting volume of the power piston cylinder easily. In fact, there was very little difference if I started with a very large "dead space" in the glass cylinder or a much smaller dead space.

The amplitude of the initial rising of the piston and weight was essentially unchanged from one pound to five pounds, leading me to theorize that the only limit to the amount of weight that can be set into motion is the pressure rating of the chamber and everything associated.

Unfortunately, the brass displacer rod bushing leaks badly over a few psi unless I apply thick oil constantly. I'll have to redo with a lip seal and larger rod or make a purely magnetic actuation system. After this I can test to much higher weights and pressures. I have tested the epoxy displacer chamber to 15 psi, and if the whole thing is put into a pressure chamber it could likely hold much higher.

Heat isn't a substance, it's manifested as a flow of energy from a hotter body to a colder body.
Energy is neither created nor destroyed, but it can get translated from one thing to another. In our example, the extra Joule started out as additional energy passed from the external energy source into the gas, and ended up as one Joule's worth of gravitational potential energy stored in the piston. So the extra Joule didn't make the gas any hotter, because bits of it were getting stored in the piston as GPE as it rose.

While I understand that heat isn't a substance, doesn't exist, and is just a manifestation of internal energy, the fact is that fire is hot. And fire expands gas. So as far as I'm concerned when doing real world experiments, heat is what I'm after. The rejection of heat is seen as a measure of efficiency.

Let's start saying 1000 Joules just to give this some scale.

I have not yet seen any data showing where or how the extra 1000 Joules are used by the gas to lift 1000 Newtons, as compared to just expanding against the atmosphere.

Further, I have not seen clear evidence or even sound theory that this internal energy, expressed as higher temperature, degrades in any manner other than conduction to a colder body.

The mechanism of conversion from internal energy to GPE, aside from thermal transfer, is what interests me.

I suggested an example a while back of an isolated room with a certain amount of internal energy and an equal amount of weight to be raised. If all the weight was raised using the energy contained within, would the room reach absolute zero?

An isolated room, not to be confused with a closed room, is a room completely closed to everything. Nothing passes in or out. A closed room has a different definition.

An isolated room can be at any temperature or pressure and contain any amount of internal energy, or enthalpy. However it won't have any ability to do work unless there is an energy difference. Examples: separate hot and cold spaces. High and low pressure tanks. A flywheel spinning relative to a base. Mass held up by a releasable latch. Batteries, fuel and oxidizer, compressed spring, ... Etc... No weight can be raised unless there is an energy differential.

If a hot and cold space exist, use them soon as eventually they will equalize and again zero work will be able to be done. This is true, and the energy is still in the room it has just equalized.

Let's start saying 1000 Joules just to give this some scale.
I have not yet seen any data showing where or how the extra 1000 Joules are used by the gas to lift 1000 Newtons, as compared to just expanding against the atmosphere.

Are we going to scale up the volume of air to 100,000cc too?
This matters because if the weight the gas is going to lift is very large in relation to the volume, it's going to compress and raise the temperature of the gas significantly before any lifting by raising pressure with externally applied thermal energy even begins. That would mean extra calcs and make the example more complex and easier to misunderstand.

I have not seen clear evidence or even sound theory that this internal energy, expressed as higher temperature, degrades in any manner other than conduction to a colder body.

The word 'degrades' seems to be doing strange work here. Energy can be translated and converted from one form to another in all sorts of ways. None of it is lost, but because energy conversion from one form to another desired form isn't 100% efficient, some of it tends to end up as 'low grade heat' - a form of energy which is hard to utilise in any useful way. Is that what you mean by 'degrades'?

The mechanism of conversion from internal energy to GPE, aside from thermal transfer, is what interests me.

The mechanism is the expansion of the gas due to the application of thermal energy. The gas expands, pushes the piston up, and the piston thus acquires additional gravitational potential energy. You can't 'see' energy being converted, but the additional GPE in the piston's mass didn't come from nowhere. It has to have arrived via the force applied to it due to the gas expansion, raising its altitude.

I suggested an example a while back of an isolated room with a certain amount of internal energy and an equal amount of weight to be raised. If all the weight was raised using the energy contained within, would the room reach absolute zero?

This raises far too many questions. How is the rooms internal energy being used to lift the weight? At what temperature and pressure does the air in the room liquify?
I think we'd better stick with more easily defined problems such as pistons in cylinders for now.

In any example, we would use the minimum amount of gas needed to do the work at hand.

By degrades, I mean into a lower temperature state. It's the action of the expanding gas "consuming" energy that I am interested in. Is internal energy really reduced when the gas expands, other than by conduction losses to the surrounding colder surfaces of the engine. And if so, how exactly?

The isolated room would of course contain high and low energy states, like a small version of the world. Any possible mechanism could be considered to perform work, using only the energy internal to the room. I realize this leads to many complex calcs, but if boiled down to the end, does the room reach 0k?

VincentG

I brought up this topic on the Physics forum the begining of last year, at least I think it is the same thing you are asking.

It was a sincere question from my point of view. My threads were being "moderated" with a heavy handed approach, for no good reason IMO, but anyway, thought you might find something interesting there:

https://www.scienceforums.net/topic/128 ... at-engine/

After the thread was closed, it seemed I was "invited" to continue in the main forum?

Hard to interpret the moderators intent. But anyway, there was a longer continuation..If I can find it.

Here it is:

https://www.scienceforums.net/topic/128 ... at-engine/

It's the action of the expanding gas "consuming" energy that I am interested in. Is internal energy really reduced when the gas expands, other than by conduction losses to the surrounding colder surfaces of the engine. And if so, how exactly?

The internal energy of the entire expanding volume isn't reduced, but the internal energy per unit volume is, because the total internal energy of the gas is spread out more, into a bigger space.

By the same token, the temperature of individual molecules of air doesn't change, but the bulk temperature of the gas does reduce, because the thermometer, or finger end, isn't getting hit so often because the molecules are more spread out or rarified in the expanded volume; the pressure falls.

This is why Charles Law holds experimentally (ignoring or minimising conduction losses with insulation)

T1/V1 = T2/V2

As the volume expands, the (bulk) temperature drops, along with the pressure, as we can see from the combined gas law

(P1V1)/T1 = (P2V2)/T2

Of course, in a real working Stirling engine, the heater is continuing to put energy into the gas while it's expanding, and this is a more complex case, because the rate of flow of energy across the wall of the cylinder will change if the temperature of the working gas inside is changing.