According to mainstream physics: Is heat "destroyed" in a heat engine?

[Tom Booth]

Alternative wordings/synonyms such as "disappears", "no longer exists", "vanishes", etc. may be substituted in place of "destroyed" (Carnot Reflections, Appendix A).

When "heat" (as a form of energy transfer) goes out of a working fluid as thermodynamic "work", my understanding is that the working fluid undergoes a drop in temperature as a result.

In other words, a change in the total energy of the gas (working fluid or air, in a hot air engine) is measurable as a change in temperature.

If the energy supplied to the engine in the form of heat goes out of the engine in a different form (mechanical motion of the piston, flywheel, etc.) Then the energy that formerly existed in the form of sensible heat, detectable with a thermometer, no longer exists within the working fluid as such, or in any other form whatsoever, latent or otherwise.

In a manner of speaking then, the "heat" has been "destroyed" utterly, as far as the energy accounting within the working fluid is concerned. That energy that has been transformed into mechanical motion must be deducted from the working fluid. This manifests as a drop in temperature.

Is this not a correct viewpoint as far as mainstream science is concerned? A natural consequence of the first law of thermodynamics (conservation of energy).?

 

 

[exchemist]

55 minutes ago, Tom Booth said:

Alternative wordings/synonyms such as "disappears", "no longer exists", "vanishes", etc. may be substituted in place of "destroyed" (Carnot Reflections, Appendix A).

When "heat" (as a form of energy transfer) goes out of a working fluid as thermodynamic "work", my understanding is that the working fluid undergoes a drop in temperature as a result.

In other words, a change in the total energy of the gas (working fluid or air, in a hot air engine) is measurable as a change in temperature.

If the energy supplied to the engine in the form of heat goes out of the engine in a different form (mechanical motion of the piston, flywheel, etc.) Then the energy that formerly existed in the form of sensible heat, detectable with a thermometer, no longer exists within the working fluid as such, or in any other form whatsoever, latent or otherwise.

In a manner of speaking then, the "heat" has been "destroyed" utterly, as far as the energy accounting within the working fluid is concerned. That energy that has been transformed into mechanical motion must be deducted from the working fluid. This manifests as a drop in temperature.

Is this not a correct viewpoint as far as mainstream science is concerned? A natural consequence of the first law of thermodynamics (conservation of energy).?

 

 

"Destroyed utterly" is a misleading phrase, as it suggests the heat vanishes without trace which, of course, does not happen. Energy, being conserved, is converted into other forms of energy. It is never destroyed. In this case some of the internal energy in heat has been converted into work. So yes, the total amount of heat has been reduced. 

Your question is such a basic one, and your choice of terms so peculiar, that I can only assume this is a disingenuous question on your part, preparing the ground for another chapter of your stubborn - and increasingly tedious - crankery (KICK 😁).  

Edited February 13, 2023 by exchemist

[Genady]

48 minutes ago, Tom Booth said:

Alternative wordings/synonyms such as "disappears", "no longer exists", "vanishes", etc. may be substituted in place of "destroyed"

In my studies of thermodynamics, I have never seen such expression or its equivalents in any textbook. Then, according to the mainstream physics: No.

[Tom Booth]

41 minutes ago, exchemist said:

(KICK 😁).

Could you please define/translate/explain that. I'm not familiar with that acronym or whatever, text slang? And find nothing in a search that clarifies it for me.

[swansont]

1 hour ago, Tom Booth said:

If the energy supplied to the engine in the form of heat goes out of the engine in a different form (mechanical motion of the piston, flywheel, etc.) Then the energy that formerly existed in the form of sensible heat, detectable with a thermometer, no longer exists within the working fluid as such, or in any other form whatsoever, latent or otherwise.

In a manner of speaking then, the "heat" has been "destroyed" utterly, as far as the energy accounting within the working fluid is concerned

It’s been converted to another form, just as the first law of thermodynamics describes.

 

 

[Genady]

If I have a flat sheet of paper and then roll it into a cylinder, did the flat sheet disappear, vanish, etc.? Certainly, not.

Edited February 13, 2023 by Genady

[sethoflagos]

1 hour ago, exchemist said:

KICK

= Kinetically Imparted Common Knowledge

[Tom Booth]

4 hours ago, swansont said:

It’s been converted to another form, just as the first law of thermodynamics describes.

 

 

Could you be more specific?

What is meant by "converted to another form" exactly?

4 hours ago, Genady said:

If I have a flat sheet of paper and then roll it into a cylinder, did the flat sheet disappear, vanish, etc.? Certainly, not.

Is that what "another form" means?

The heat is rolled up into a different shape, but is still there as a constituent part of the working fluid?

[Lorentz Jr]

33 minutes ago, Tom Booth said:

What is meant by "converted to another form" exactly?

Heat in matter is energy in the form of random (i.e. uncorrelated) motions of molecules, atoms, and the subatomic particles inside them. That energy can be converted to other forms, for instance the kinetic energy of an automobile powered by an internal combustion engine.

Edited February 14, 2023 by Lorentz Jr

[Tom Booth]

6 hours ago, Genady said:

In my studies of thermodynamics, I have never seen such expression or its equivalents in any textbook. Then, according to the mainstream physics: No.

I could provide some references where such expressions have been used from my own reading and research. Just one example for now, but certainly not an isolated case:

Quote

SECOND LAW OF THERMODYNAMICS
Garnet's Heat Engine
Definition of terms

1. Heat engine.

A heat engine is any mechanical contrivance by means of which heat is converted into work.

Steam engines, gas engines, oil engines, hot-air engines are all forms of heat engines.

All heat engines exhibit the characteristic that heat disappears during the performance of work....

2. Cycle of operations.

In every form of heat engine the transformation of heat into work is effected by subjecting some suitable substance to a cycle of operations (expansion, compression, condensation, etc.), so arranged that the work done by the substance during the cycle is
greater than the work done on it, and useful external work is done at the expense of the heat supplied to the substance.

From the First Law of Thermodynamics the amount of work performed by the gas on external bodies during the cycle must be equal to the heat which has disappeared.

ADVANCED LECTURE NOTES ON HEAT
BY J. R. ECCLES, M.A. (Cambridge University Press, 1921)

In this case, the term "disappears" is used.

[Lorentz Jr]

18 minutes ago, Tom Booth said:

In this case, the term "disappears" is used.

Maybe the word is a bit overdramatic. It doesn't mean the energy ceases to exist.

[exchemist]

8 hours ago, Tom Booth said:

Could you please define/translate/explain that. I'm not familiar with that acronym or whatever, text slang? And find nothing in a search that clarifies it for me.

It is a reference to my metaphor, in your previous thread, for your behaviour on this forum. I said you were trying to playing the victim while wandering about with a huge "Kick me" sign strapped to your arse. And that that is why you get kicked, by me and others.

Now perhaps, in turn,  you can enlighten us as to why you are so preoccupied with the precise word one uses to describe the conversion of heat into work.

(I note that you have not been able to turn up a reference to heat being "destroyed" or "destroyed utterly", and I bet that is not for want of trying.)

Edited February 14, 2023 by exchemist

[Ghideon]

3 hours ago, Tom Booth said:

In this case, the term "disappears" is used.

The idea that heat "disappears" during the performance of work in a heat engine seems to be a reasonable a way of expressing the fact that heat energy is converted into other forms of energy, such as mechanical work or kinetic energy, and is no longer available as heat. Note that text was written 1921 and science, and associated descriptions, may have moved on since then.

 

4 hours ago, Tom Booth said:

Could you be more specific?

What is meant by "converted to another form" exactly?

The terminology used to describe the conversion of heat energy into other forms of energy can vary depending on the context and level of detail of the discussion. For example, in some contexts, it may be more appropriate to say that the heat energy is "transferred" or "converted" rather than "disappears", since the energy is still present but has changed form. Similarly, the specific mechanisms by which heat energy is converted into work or other forms of energy may be described in different ways depending on the level of detail and the theoretical framework being used. For instance:

Level of detail: At a general level, the focus may be on the overall efficiency or performance of a heat engine or energy system, without necessarily specifying the exact mechanisms of energy transfer or conversion.

Context: For example, in the context of engineering or applications, the terminology may be more technical and focused on the practical aspects of energy conversion and efficiency. In the context of a more theoretical or scientific discussion, the terminology may be more abstract.

Theoretical framework: The specific theoretical framework being used to describe thermodynamic phenomena can also have an impact on the terminology used.

Note that for more understanding and for adding ability to predict behaviour you may use models and mathematics in addition to written descriptions. Hope this helps guiding you toward the more specific answer you requested.

Edited February 14, 2023 by Ghideon

[Genady]

4 hours ago, Tom Booth said:

Quote

ADVANCED LECTURE NOTES ON HEAT
BY J. R. ECCLES, M.A. (Cambridge University Press, 1921)

In this case, the term "disappears" is used.

 

10 hours ago, Genady said:

In my studies of thermodynamics, I have never seen such expression or its equivalents in any textbook.

 

Excuse me, but in my studies of thermodynamics, textbooks printed in 1921 were not employed.

 

5 hours ago, Tom Booth said:

The heat is rolled up into a different shape, but is still there as a constituent part of the working fluid?

No. The energy is rolled up into a different shape. The heat was not a constituent part of the working fluid to start with.

[exchemist]

4 hours ago, Tom Booth said:

I could provide some references where such expressions have been used from my own reading and research. Just one example for now, but certainly not an isolated case:

In this case, the term "disappears" is used.

None of this quibbling about words gets us anywhere. In the particular case of Carnot, you are reading a translation from early c.19th French. Assuming the original of "destroyed" was "détruit", that could be translated as destroyed, demolished, done away with, effaced, suppressed....

The idea is that (some of) the heat has gone and is no longer there. This is true, it has gone - into work. 

[Genady]

@Tom Booth,

In my sheet of paper analogy, the sheet of paper represents energy:

- When the sheet is cylindrical, it is not flat. When the energy is in a form of work, it is not in a form of heat. Shape/form changes - not destroyed.

- Being flat is not a constituent part of anything, it is a shape of the sheet. Heat is not a constituent part of anything, it is a form of energy.

Edited February 14, 2023 by Genady

[studiot]

This whole discussion seems to me to be a rather silly argument.

Energy is not destroyed when work is done. It just goes somewhere else.

The concept of heat as a substance was replaced by the concept of 'internal energy of a system'.

All systems have internal energy. When they do work or transfer heat this becomes an increase in the internal energy of another system (generally called the surroundings).

This increase in the internal energy of the surroundings is matched by (equal to) a corresponding decrease in the system doing the work or transferring the heat.

Energy itself is not a substance, it is a property of a system.

Internal energy can be held within a system in several different ways, which we distinguish as different 'forms' of 'energy'.

This concept leads to one version of the First Law as The energy of an "isolated system is constant", which is consistent with the more oft quoted  dE = q+w.

 

@Tom Booth

I suggest if you genuinely want further understanding then you study the terms open, closed and isolated; energy,  internal energy, potential energy, mechanical energy, electrical energy, so that you can put these concepts into their proper place.

[iNow]

I love that y’all are still engaging this guy as if there’s ever been any semblance of good faith whatsoever in any of his posts. Hope springs eternal, I reckon. 

[joigus]

There's so much one can do with words.

As said above, a system stores energy, not heat. It can give it out, off or away by means of work or heat exchange.

Words in science are as good as the mathematical concepts they help us remember, the precise experimental operations they represent, etc.

[Genady]

@Tom Booth,

Here are examples of the textbook language as of 2021, as opposed to 1921, from Steven Weinberg, Foundations of Modern Physics, Cambridge University Press, 2021:

Quote

The first step in the development of thermodynamics was the recognition that heat is a form of energy.

Quote

it picks up small net amounts dQ of heat energy from the environment

Quote

the first law is just the conservation of energy, discussed in the context of heat energy

In many places he uses the word 'heat', but it is always simply a short for the phrase 'heat energy'. 

Thus, to say that 'heat is destroyed' would be the same as saying that 'heat energy is destroyed', and this would be certainly wrong.

[Tom Booth]

Maybe if the word "heat" can be avoided, or more strictly defined.

Heat is technically, I think, a temperature dependent transfer of energy.

Would that be an accurate statement?

If so, then somewhat euphemistically I guess, if there are two objects in close proximity, one at a high temperature and another at a low temperature then "heat" could be said to exist between them. There can be a temperature dependent transfer of energy between the two objects.

If, by some means, we were to cool down the hotter object (lower it's temperature by taking away some of its energy) so that there is no longer a temperature difference, then there can no longer be this temperature dependent transfer of energy. "Heat" between the two objects, then, no longer exists.

By "destroying" the ∆T we have also "destroyed" the potential for there to be any temperature dependent  transfer of energy. (as a statistical average at least, there are still energy transfers but they tend to balance out or nullify each other on the whole)

Are these fair statements so far?

Heat, as a temperature dependent transfer of energy can either exist, or not exist, it could be "destroyed" or "created" by either adding or subtracting energy from one side or the other (one object or the other).

This is no violation of the first law of thermodynamics, to assert that heat as such, as a temperature dependent energy transfer, either exists, or not, can be created or destroyed as a result of human intervention or engineering.

In other words, if I operate an engine, with the addition of some heat, thus expanding the working fluid and that expansion results in the performance of work, with the consequence that the temperature of the working fluid falls returning to a state of thermal equilibrium with the surroundings as when the operation started, before heat was introduced, then it could be said that the heat, first manifest as the introduction of a temperature difference "disappeared", "vanished" or was "destroyed" in the sense that the temperatures were equalized by a non-temperature dependent transfer of energy.

A transfer of energy by expansion of a gas is not necessarily temperature dependent. Energy can be transfered into the working fluid by the application of heat, raising the temperature of the working fluid, but the transfer of work out of the working fluid also results in a drop in temperature. This "work" is a non-temperature dependent transfer of energy, and yet the temperature of the working fluid drops as a consequence, and the "heat" as a temperature dependent means of energy transfer ceases to exist, or vanishes, as there is no longer any possibility for making any temperature dependent energy transfer. The temperatures have been equalized by other means. By the transfer of energy as "work" which is not a temperature dependent energy transfer.

When a quantity of "work" is performed by the working fluid, the capacity for energy transfer via heat has been diminished in equal quantity. The temperature difference has been "destroyed" as a result of the work output.

 

Edited February 14, 2023 by Tom Booth

[Bufofrog]

14 minutes ago, Tom Booth said:

If, by some means, we were to cool down the hotter object (lower it's temperature by taking away some of its energy) so that there is no longer a temperature difference, then there can no longer be this temperature dependent transfer of energy. "Heat" between the two objects, then, no longer exists.

By "destroying" the ∆T we have also "destroyed" the potential for there to be any temperature dependent  transfer of energy. (as a statistical average at least, there are still energy transfers but they tend to balance out or nullify each other on the whole)

Are these fair statements so far?

I would say these statements are not clear enough and could lead to confusion.  The clearest statement is that there was heat transfer from hot to cold. 

[studiot]

23 minutes ago, Tom Booth said:

Maybe if the word "heat" can be avoided, or more strictly defined.

Heat is technically, I think, a temperature dependent transfer of energy.

Would that be an accurate statement?

Not always, no.

 

What about the heat of combustion ?

What about latent heat ?

[exchemist]

9 minutes ago, Bufofrog said:

I would say these statements are not clear enough and could lead to confusion.  The clearest statement is that there was heat transfer from hot to cold. 

But you don't understand: confusion is the object of the exercise. 😄

[Bufofrog]

28 minutes ago, exchemist said:

But you don't understand: confusion is the object of the exercise. 😄

I'm afraid you're probably right.