Experimental Studies of the Internal Energy of a real fluid

[Matthew Marko]

https://www.nature.com/articles/s41598-022-11093-z

In this new 2 May 2022 publication, an experimental effort was made to measure directly the internal energy changes of non-ideal CO2, from the decrease in temperature as the liquid-gas expanded from one cylinder into two. With the empirical equation proposed and experimentally validated in this manuscript, it is argued that a Stirling cycle heat engine that exceeds the Carnot efficiency is possibly (theoretically); such a heat engine has obviously never been built in practice. Does the empirical assumptions of internal energy of a non-ideal fluid make such a case, or does anyone have a countering reference of some direct measurements of a non-ideal fluid that will argue otherwise?

 

[vanhees71]

Without having looked at the paper, this seems highly suspicious since it would violate the 2nd law, according to which the Carnot efficiency is the largest possible, or do I misunderstand your statement. I'll have a look at the paper later (with a typo already in the title, which makes it a bit suspicious although it's published in Nature).

https://en.wikipedia.org/wiki/Carnot's_theorem_(thermodynamics)

 

[Matthew Marko]

Without having looked at the paper, this seems highly suspicious since it would violate the 2nd law, according to which the Carnot efficiency is the largest possible, or do I misunderstand your statement. I'll have a look at the paper later (with a typo already in the title, which makes it a bit suspicious although it's published in Nature).

https://en.wikipedia.org/wiki/Carnot's_theorem_(thermodynamics)

I do not see a typo in the title.

The paper discusses Carnot's theorem, and compares the traditional way of calculating internal energy of a non-ideal gas (eq 7 in the manuscript) to the empirical equation (eq 3 and 4) that if accurate will allow for a heat engine to exceed the Carnot efficiency due to the Van der Waal forces; then the paper shows the experiment suggesting eq 3 matches closer than eq 7. But I welcome you to reply after having read it.

 

[Matthew Marko]

Without having looked at the paper, this seems highly suspicious since it would violate the 2nd law, according to which the Carnot efficiency is the largest possible, or do I misunderstand your statement. I'll have a look at the paper later (with a typo already in the title, which makes it a bit suspicious although it's published in Nature).

https://en.wikipedia.org/wiki/Carnot's_theorem_(thermodynamics)

This article isn't the first, in New Journal of Physics in 2018, it was proposed it is possible to exceed the Carnot efficiency at the quantum level:
https://doi.org/10.1088/1367-2630/aa8ced

Both Scientific Reports and NJOP are legitimate journals. Again, nobody could argue that the second law is false, at least for a macroscopic ideal gas; it is intuitively obvious. Just perhaps theoretical circumstances.

 

[vanhees71]

I do not see a typo in the title.

It's van der Waals.

 

[Lord Jestocost]

This article isn't the first, in New Journal of Physics in 2018, it was proposed it is possible to exceed the Carnot efficiency at the quantum level ...

On the other hand, one reads:

"The Carnot statement of the second law of thermodynamics poses an upper limit on the efficiency of all heat engines. Recently, it has been studied whether generic quantum features such as coherence and quantum entanglement could allow for quantum devices with efficiencies larger than the Carnot efficiency. The present study shows that this is not permitted by the laws of thermodynamics – independent of the model. We will show that rather the definition of heat has to be modified to account for the thermodynamic cost for maintaining non-Gibbsian equilibrium states. Our theoretical findings are illustrated for two experimentally relevant examples."

Bartlomiej Gardas and Sebastian Deffner in "Thermodynamic universality of quantum Carnot engines" (Phys. Rev. E 92, 042126, 2015)

 

[Chestermiller]

Matthew,

It looks like you are the author of this article, but you seem to have some serious reservations about it. What is that all about?

I also have serious reservations, but not because of the Sterling cycle efficiency part. I have problems with the fundamental thermodynamics related to determining the contribution of non-ideality to the internal energy change.

Has this paper actually appeared yet in Nature, or is it just in the review stage right now? If so, have the reviewers come back with comments yet?

 

[Matthew Marko]

Matthew,

It looks like you are the author of this article, but you seem to have some serious reservations about it. What is that all about?

I also have serious reservations, but not because of the Sterling cycle efficiency part. I have problems with the fundamental thermodynamics related to determining the contribution of non-ideality to the internal energy change.

Has this paper actually appeared yet in Nature, or is it just in the review stage right now? If so, have the reviewers come back with comments yet?

My apologies for the delay, oddly I didn't get the alert. I am the author, and the paper has passed peer review. Surprisingly with two reviewers post said publish as is (beyond some figure recommendations). It is an accepted and published paper.

I would be interested in discussing further your thoughts. Please.shoot me an email mattdmarko@gmail.com