Heat Flow

[Willem F Esterhuyse]

When something cools down it gets colder, hence it's coldness increased, so can't you say that coldness flowed into the warmness?

[John Cuthber]

If you like.
But rewriting thermodynamics as cryodynamics doesn't really achieve much.

People have given some thought to it.
https://lifeboat.com/blog/2013/07/short-summary-of-a-new-idea-cryodynamics

[Ghideon]

  On 2/17/2023 at 8:39 AM, Willem F Esterhuyse said:

When something cools down it gets colder, hence it's coldness increased, so can't you say that coldness flowed into the warmness?

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Since this is speculations, what is your reasoning and arguments for making this claim?

 

(The answer according to established models is "No, it is not correct to say that coldness flows into warmness when something cools down. ")

Edited February 17, 2023 by Ghideon
x-post

[exchemist]

  On 2/17/2023 at 8:39 AM, Willem F Esterhuyse said:

When something cools down it gets colder, hence it's coldness increased, so can't you say that coldness flowed into the warmness?

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This reminds me of Spike Milligan:" Hey, who turned on the dark?"

You get into trouble with the idea of "coldness" when you have to deal with absolute zero. You can't make something as cold as you like, whereas you can make something as hot as you like.  So there's an asymmetry there. Just as, with light, you can make something as bright as you like but you can't make it as dark as you like.

[Lorentz Jr]

  On 2/17/2023 at 8:39 AM, Willem F Esterhuyse said:

When something cools down it gets colder, hence it's coldness increased, so can't you say that coldness flowed into the warmness?

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Sure, as long as it doesn't get too cold. It's similar to modeling electric current as a flow of "holes", which are gaps in the electron density in a conductor. It works as long as there's something left to remove.

Edited February 17, 2023 by Lorentz Jr

[Genady]

dU = δQ + δW

It does not matter what one calls δQ as long as the equation holds. You can also say, "the warmness flaws out and the coldness flows in" or "the coldness replaces the warmness", etc.

 

[studiot]

  On 2/17/2023 at 8:39 AM, Willem F Esterhuyse said:

When something cools down it gets colder, hence it's coldness increased, so can't you say that coldness flowed into the warmness?

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It's not a good idea for several reasons.

The original caloric theory of heat was a two substance theory, heat and cold.

Of course today know that neither heat nor cold are actual substances.

It was also realised that two substance theories cannot explain all phenomena, for example what happens when a pure substance melts or solidifies.

What flows which way then ?

Another difficulty is that cold is incompatible with the idea of internal energy, since energy is a positive definite quantity, what sort of quantity is cold that can reduce it ?

[sethoflagos]

  On 2/17/2023 at 8:39 AM, Willem F Esterhuyse said:

When something cools down it gets colder, hence it's coldness increased, so can't you say that coldness flowed into the warmness?

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It's quite reasonable I think to say something along the lines of 'the climate gets cooler as winter draws near'. 

But when we try to express such ideas in physics, we run into the conventional understanding that the total energy content of a material is always positive. At a fundamental level, if you accepted the concept of negative total energy, you would de facto be accepting the concept of negative mass. This is not observed. 

[MigL]

Why complicate matters.
The current systen has been worked out over a couple of hundred years to be self-consistent.

[Willem F Esterhuyse]

  On 2/17/2023 at 8:50 AM, Ghideon said:

Since this is speculations, what is your reasoning and arguments for making this claim?

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The logic is: it gets to have a larger quantity of coldness. And water flows to make a larger quantity of water.

[Genady]

  On 2/18/2023 at 8:24 AM, Willem F Esterhuyse said:

it gets to have a larger quantity of coldness

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What do you refer to as "it"?

A larger quantity of coldness, where?

Let's say a body A gets colder and a body B gets warmer. Can you rephrase your statement for this case?

[Lorentz Jr]

  On 2/18/2023 at 10:26 AM, Genady said:

What do you refer to as "it"?

A larger quantity of coldness, where?

Let's say a body A gets colder and a body B gets warmer.

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A

[Genady]

  On 2/18/2023 at 10:32 AM, Lorentz Jr said:

A

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AFAIK, there is no such a thing as "a quantity of heat in a body". For the same reason, there cannot be a meaningful concept of "a quantity of coldness in a body."

[studiot]

  On 2/18/2023 at 10:41 AM, Genady said:

AFAIK, there is no such a thing as "a quantity of heat in a body". For the same reason, there cannot be a meaningful concept of "a quantity of coldness in a body."

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Engineers still use the term Heat Content (AKA enthalpy).

 

  On 2/18/2023 at 8:24 AM, Willem F Esterhuyse said:

The logic is: it gets to have a larger quantity of coldness. And water flows to make a larger quantity of water.

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Are you going to answer my question ?

  On 2/17/2023 at 12:05 PM, studiot said:

for example what happens when a pure substance melts or solidifies.

What flows which way then ?

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[Genady]

  On 2/18/2023 at 10:47 AM, studiot said:

Engineers still use the term Heat Content (AKA enthalpy).

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Thank you, I did not know. Found it here: Enthalpy - Wikipedia

It says,

  Quote

This is why the now-obsolete term heat content was used in the 19th century.

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Perhaps, not so obsolete, then.

PS. Maybe this is another example that belongs to this thread: 

 

[Willem F Esterhuyse]

  On 2/18/2023 at 10:26 AM, Genady said:

What do you refer to as "it"?

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A general object.

  On 2/18/2023 at 10:26 AM, Genady said:

A larger quantity of coldness, where?

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In body A.

  On 2/18/2023 at 10:47 AM, studiot said:

Are you going to answer my question ?

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  On 2/18/2023 at 10:47 AM, studiot said:

The logic is: it gets to have a larger quantity of coldness. And water flows to make a larger quantity of water.

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Then reason like Syllogism: replace "water" with "coldness" and  compare with the left sentence.

[Genady]

  On 2/18/2023 at 12:36 PM, Willem F Esterhuyse said:

In body A

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As I've said above, there is no such a thing as "a quantity of heat in a body". Following your logic, there cannot be such a thing as "a quantity of coldness in a body."

[Willem F Esterhuyse]

They postulated a quantity called "phlogiston". On a abstract level it makes sense.

[Genady]

  On 2/18/2023 at 12:48 PM, Willem F Esterhuyse said:

They postulated a quantity called "phlogiston". On a abstract level it makes sense.

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Since they did it, they have figured out that it does not work on any level, and have it abandoned.

[exchemist]

  On 2/18/2023 at 12:41 PM, Genady said:

As I've said above, there is no such a thing as "a quantity of heat in a body". Following your logic, there cannot be such a thing as "a quantity of coldness in a body."

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But isn't that just because we now speak of internal energy, and use "heat" to describe the flow of internal energy rather than the energy itself?

I should have thought one could say that a body at absolute zero has no heat energy left in it. All that's left is is zero point energy, and various kinds of potential energy, including rest energy, none of which is extractable as heat.  

[Genady]

  On 2/18/2023 at 12:51 PM, exchemist said:

But isn't that just because we now speak of internal energy, and use "heat" to describe the flow of internal energy rather than the energy itself?

I should have thought one could say that a body at absolute zero has no heat energy left in it. All that's left is is zero point energy, and various kinds of potential energy, including rest energy, none of which is extractable as heat.  

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As you're well aware, internal energy can change without any heat flow. Thus, the OP analogy with "a quantity of water in the body" would not hold.

[swansont]

  On 2/18/2023 at 8:24 AM, Willem F Esterhuyse said:

The logic is: it gets to have a larger quantity of coldness. And water flows to make a larger quantity of water.

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Can you add coldness to something that has its maximum amount of coldness? Why not?

[exchemist]

  On 2/18/2023 at 1:00 PM, Genady said:

As you're well aware, internal energy can change without any heat flow. Thus, the OP analogy with "a quantity of water in the body" would not hold.

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OK but surely one can define "heat energy" or "thermal energy" as a subset of total internal energy, meaning that portion of the internal energy due to kinetic energy of molecules, which is the same as that portion of it that can be made to flow out by means of a temperature gradient.  Heat energy, so defined, is reduced to zero at absolute zero, is it not?

 

[Willem F Esterhuyse]

  On 2/18/2023 at 1:42 PM, swansont said:

Can you add coldness to something that has its maximum amount of coldness? Why not?

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No, because there is no negative free paths for molecules.

[Genady]

  On 2/18/2023 at 2:22 PM, exchemist said:

OK but surely one can define "heat energy" or "thermal energy" as a subset of total internal energy, meaning that portion of the internal energy due to kinetic energy of molecules, which is the same as that portion of it that can be made to flow out by means of a temperature gradient.  Heat energy, so defined, is reduced to zero at absolute zero, is it not?

 

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Yes, it is.

You're talking about enthalpy, right?