Talk:Carnot heat engine

Comments

Is the Carnot cycle real one that we can use it in making engine? The diagram shows the Entropy/Temperature version of the Carnot cycle. I think that most people would find the Pressure/Volume version more meaningful though. -- Derek Ross | Talk

Fixed your comments, hope you don't mind. It did not make sense as it was stated in its original form. To answer your question, the Carnot Engine is not an actual device that you can build in your basement. Its a theoretical device which could only function in a complete vaccuum.Sunshine Warrior04 (talk) 06:05, 5 April 2012 (UTC)

 agreed128.120.57.116 07:26, 7 December 2006 (UTC)

As i understand the significance of Carnot cycle is on it's T/S diagram, not on the p/V.--Arcsinx 22:24, 10 May 2007 (UTC)

The curve over the rectangle is not needed in principle. Supposedly that is the phase-change curve. The illustration is one suitable for presenting that a Rankine (vapor) cycle is in principle equivalent to the Carnot cycle. MGTom 10:09, 2005 Feb 15 (UTC)

You might want to look at the diagrams that I made for the Hebrew wikipeida's article: eman 01:49, 17 Feb 2005 (UTC)

In principle: that's it. It would be nice if on the the p-V diagram the hyperbolic nature of the relation would be more evident. Of course the presented processes are on a cut-out of the full p-V diagram, ... Nothing more can be done on the T-s, is dull anyway. MGTom 09:55, 2005 Feb 17 (UTC)

Might it be better for the list of steps to read 1-2, 2-3, 3-4, 4-1, given that the processes described happen along the vertices of the graph rather than at the corners? This confused me at first glance, and I think this would remove some of the ambiguity Jakob 19:30, Apr 8, 2005 (UTC)

I removed figure 2 because it was wrong. It described an external combustion Brayton Cycle instead of a Carnot Cycle. Plc123 01:58, 22 March 2007 (UTC)

It is said at the describeing of a real heat engine, that the temperature of the system is in an open interval of ]T_H,T_C[, but lower on a picture compareing a real- and the Carnot-cycle both of them shows the temperature in a closed interval of [T_H,T_C], but the corollary of the 2nd rule of thermodynamics is that only a theoretical cycle (e.g. Carnot cycle) can reach these extreme values...--Arcsinx 23:04, 10 May 2007 (UTC)

Reheaters and regenerators

I know little about thermodynamics, but I found this article valuable, although I would suggest that perhaps we need either some explaination for this line:

"This can help illustrating, for example, why a reheater or a regenerator can improve thermal efficiency."

...or, perhaps pages that explain what a reheater and a regenerator are.

Thanks to all contributors for the great work.

Eric 18:39, 24 Jun 2005 (UTC)

I have tried to tidy that paragraph but it is still obscur to me what the sentence is getting at. Cutler 15:57, July 13, 2005 (UTC)

Benoit

'"Thomas Benoit+Carnot' gets 2 (sic) google hits [1] of which one is a fork of this article. The other doesn't offer much. I have so far found no trace of Thomas Benoit but will keep trying a bit longer.

Is is possible that this is a misprint for Benoit Paul Émile Clapeyron? He would fit. Cutler 16:07, July 13, 2005 (UTC)

I think, based on the Émile Clapeyron entry, that it's more than possible, and I was so bold as to change it. -Paul 02:12, 2005-08-15 (UTC)

Name/move suggestion?

The phrase "Carnot heat engine" is used rarely, if ever in the article, so I think we should move it to "Carnot Cycle".

Yes this is a wise suggestion. I will make the change. The term “Carnot cycle” is one of the most famous terms in all thermodynamics and engine theory. In 1834, Clapeyron called it a “cycle of operations.” In the 1850s and 60s Clausius found the them “cycle” to be of such importance that he italicized it; you can read parts of his memoirs here<<link removed>>Nishkid64 (talk) 20:41, 30 October 2007 (UTC). One can pick up any thermodynamics textbook and find the Carnot cycle to be the core of the book.

The Carnot heat engine should be a separate article on its own standing. I will start the stub and upload a Carnot heat engine diagram.--Sadi Carnot 20:56, 16 July 2006 (UTC)

How do we see the two articles developing? It seems like we might just redirect 'Carnot heat engine' to 'Carnot cycle'. Thoughts? Tom Harrison ^Talk 18:51, 17 July 2006 (UTC)

I just up loaded two new heat engine diagrams for the Carnot heat engine page:

,

The Carnot heat engine is an historical topic, e.g. Cengel and Boles’ Thermodynamics (textbook) has a separate section for each, one for the engine, one for the cycle. The main focus of the cycle should be on the PV-diagram, reversibility, and work-output, etc.; the engine article, the most famous of all engine models, should talk about efficiency, the second law, temperatures differences, structural configurations, etc. This is just a quick sketch.--Sadi Carnot 20:52, 17 July 2006 (UTC)

Equation 3?

i had no idea what this was referring to until i looked at Carnot cycle. someone needs to fix this. looks like a lot of duplication, etc.

Wait! Carnot Cycle redirects here while Carnot cycle is a different article. great job guys!  ;) --pfunk42 04:15, 21 July 2006 (UTC)

I've fixed the redirect. Thanks for pointing it out. Tom Harrison ^Talk 13:24, 21 July 2006 (UTC)

Gas Turbine addition

I really don't like the addition of the gas turbine diagram and plots.

• It gives the impression that the Carnot cycle is equivalent to a gas turbine engine.
• The diagram gives no explanation of how it relates to a Carnot cycle.
• The plots of efficiency are simple plots of 1-Th/Tc, and they take up a lot of room for such a simple equation.
• This is an application, its not a demonstration of the Carnot cycle.

PAR 18:18, 4 December 2006 (UTC)

Equations - not well explained

Why does this page have surface integrals and line integrals before simpler equations relating to carnot efficiency? The article doesn't even explain that those integrals *are* surface integrals and line integrals - and it doesn't label its variables well. This page needs to work on its accessibility to non-experts. Fresheneesz 00:09, 16 January 2007 (UTC)

I agree, casually passing by to grab the formula for physics homework I was disapointed that the simple equations were not present on the page. ~AlvinBlah

I have a couple of comments: first, note that a complaint concerning equation 3 is in its own section on this talk page and should be relocated here; and, second, I notices that, unless its farther down on the page somewhere, η (eta) doesn't seem to reside in the list of variables put by one of the authors after equation 1. BCG999 Out. (talk) 17:07, 12 December 2011 (UTC)

use?

i've never heard of anyone actually using the cycle in a real engine-is this simply because of the large volume requirements, or the result of something else? 69.163.197.224 14:45, 25 January 2007 (UTC)

impracticality. notice that a lot of assumptions made about the cycle is impossible to achieve in practice. as stated in the intro of article, the cycle is reversible, i.e. it creates no entropy, i.e. it has perfect efficiency (for any given T_H and T_C). the Carnot cycle is something one aims to achieve. the closer to the Carnot cycle the better the engine, although one usually doesn't even come close. Mct mht 16:02, 25 January 2007 (UTC)

Carnot cycle sure has a very good efficiency, but it needs an infinite amount of time in order for the system to give/receive energy isothermally. So that power output=0W. —Preceding unsigned comment added by Eric DUMINIL (talk • contribs) 11:05, 28 November 2007 (UTC)

it's theory -- you use it rhetorically

for instance, you can talk about the carnot cycle when calculating the energy savings from rigging a fountain pump to the condensation outlet vent on your air conditioner and squirting the condensate onto the radiator outside your house, just for instance mind you —Preceding unsigned comment added by 208.190.202.56 (talk) 03:34, 17 October 2007 (UTC)

T-V or P-V diagrams

Shouldn't we have T-V or P-V diagrams too instead of just T-S diagrams to explain the cycle better? 220.227.165.210 (talk) 08:42, 15 September 2008 (UTC)

Actually just P-V diagrams to calculate the work done. 220.227.165.210 (talk) 08:44, 15 September 2008 (UTC)

Gah I'm confused 220.227.165.210 (talk) 08:47, 15 September 2008 (UTC)

Wrong Carnot

Wasn't it developed by Lazare Carnot??? 88.104.47.64 (talk) 13:04, 10 January 2009 (UTC)

Who is Gangbangin Gallagher?

I came across this article just perusing Wikipedia, and I was struck by this name. Does anyone know who Gangbangin Gallagher is, as mentioned in the "Modern Diagram" section? Sounds like a Wikibomb. — Preceding unsigned comment added by 67.171.198.15 (talk) 02:12, 29 February 2012 (UTC)

Edited the part on real engines

Hi,

I tried to edit the section on real engines. Hopefully it is correct and makes things a little clearer. Please let me know of suggestions to improve this. I was also wondering about editing the page on the Clausius Theorem, since that too doesn't seem well explained at all. Thanks Aritrop (talk) 22:20, 23 February 2015 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Carnot heat engine/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Are you sure this is an A-class quality? It doesn't even have references! Arkwatem 09:47, 24 September 2007 (UTC)

Last edited at 09:47, 24 September 2007 (UTC). Substituted at 10:57, 29 April 2016 (UTC)

Figures

Some figures are numbered, some are not. The figure that seems to be called "(1)" (but never directly referenced by the text) contains three colors, but the legend claims two different meanings for the color blue, while not identifying what the color turquoise is supposed to be.Ronburk (talk) 10:27, 12 November 2018 (UTC)

The (1) style numbers are actually for the equations on the left, not the figures on the right. I have added dashed lines to clarify it. Not so pretty but maybe another editor can do something nicer.

The 2 blues are slightly different shades but it is not very clear. Unfortunately I am not clear myself what the turquoise represents.  Stepho  talk  11:39, 12 November 2018 (UTC)

Merge?

Why do we have both this article, and a Carnot cycle article, talking about the same thing? Geoffrey.landis (talk) 14:53, 22 June 2020 (UTC)

Nonsense

The caption to one of the diagrams has:

< The entropy of a real material changes with temperature >

No, it doesn't. Consider, for example, the isentropic compression (or expansion) of a gas.

86.130.154.59 (talk) 10:46, 3 July 2020 (UTC)

Most efficient engine or most efficient heat engine?

Just saw this change by User:Stepho-wrs, where he made the change from The Carnot engine is the most efficient engine which is theoretically possible -> to -> The Carnot engine is the most efficient heat engine which is theoretically possible, as other type of engines exist. While that is true, I also wonder, isn't the Carnot engine the most efficient engine, full stop? I do believe it is, but it would be nice if someone else could confirm or deny. Thanks. AdrianHObradors (talk) 11:05, 4 June 2022 (UTC)

The mathematics in the article are stated in terms of heat engines. Therefore, they can only prove proves things about heat engines. Therefore they can't say anything about non-heat engines. To say that Carnot engines are the most efficient of all possible types of engines requires a reliable reference to back it up. I might possibly be wrong about electrical engines being more efficient but it would still need a reference as soon as we talk about anything besides heat engines. When I do searches about the efficiency of Carnot engines from reliable sources, they always qualify it as the Carnot engine being the most efficient heat engine.  Stepho  talk  11:50, 4 June 2022 (UTC)

Hi @Stepho-wrs! Yeah, I have been thinking about it and it is probably right to leave it as "heat engine". It probably gets too complicated anyway to measure efficiency with other engines. If we are talking about an electric motor, it is turning electricity to mechanical energy, but that electricity must have come from another engine. It is an interesting subject, I might bring it up on WP:RD/S. AdrianHObradors (talk) 12:36, 4 June 2022 (UTC)

No problem.  Stepho  talk  12:47, 4 June 2022 (UTC)