Talk:Joule-Thomson effect/Draft

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 Definition The increase or decrease in the temperature of a real gas (as differentiated from an ideal gas) when it is allowed to expand freely at constant enthalpy (meaning that no heat is transferred to or from the gas, and no external work is extracted from the gas). [d] [e]
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Wikipedia has a similar article

I extensively contributed to the Wikipedia article of the same name. I would estimate that about 75 percent of the wording in that article was mine.

I reworked it somewhat in my CZ sandbox and conformed it to a CZ article format. - Milton Beychok 19:49, 17 February 2008 (CST)


1) the equation for is written as if it is a constant. Should this be written as (T,P) to reflect its dependence on the initial temperature and pressure?

2) Is there any theoretical explanation for this phenomenon, or is it typically thought of as a phenominological effect that is just measured? In other words, does it relate to electrostatic interactions between atoms/molecules, polarizability, etc? I haven't thought about the JT effect for quite some time (decades!), but I'll look around for a textbook or two and look for answers also. David E. Volk 15:49, 11 July 2009 (UTC)

3) The original reference, should you want to incorporate it is: J. P. Joule and W. Thompson, Proc. Roy. Soc. (London), 143, 357, (1853). Another fine experiment conducted in a Brewery!

4) The JT effect is valid for liquids also, not just gasses, at least according to the thermo classic text by G. N. Lewis and M. Randall, Thermodynamics, 2nd Edition, revised by Pitzer and Brewer, McGraw-Hill Series in Advanced Chemistry (1961).

David, in response to (1), I have always seen the J-T effect written simply as . I just made another Google search and all of the information I found used simply . The article does state that J-T effect "depends on the specific gas, as well as the temperature and pressure of the gas before expansion", so your point is made, don't you think?
As for (2), there probably is a theoretical mechanism that can explain the phenomenon in terms of the attractive and repulsive forces between molecules. My main focus in writing the article was to explain what the J-T effect is and how it is used in industry ... rather than trying to explain the theoretical mechanism. I know ... that is the typical engineering attitude. If you would like to add another section to the article that explains the theoretical mechanism, please do so.
In regard to (3) and 4, I will incorporate that original reference and I will include liquids in the lede.
Thanks for your comments, I really appreciate them. Milton Beychok 18:04, 11 July 2009 (UTC)
Milton, I checked my texts too and they also use as you have done, so clearly that is the standard nomenclature. As for theory, no time to work on it currently, but one day perhaps. David E. Volk 12:48, 14 July 2009 (UTC)
Milt, I may have missed it here (astigmatism sometimes does that to me) but I didn't see the elements of the equation defined. Those with the appropriate background will know what they are but not everyone will recognized the "del P" and "del T" and the "sub H". Is there a standard we use for defining the terms in an equation below the equation? Karl D. Schubert 17:57, 30 September 2009 (UTC)
Good point, Karl. I have revised the first sentence in this section to make clear what the terms in the equation mean. There are a myriad of ways used in CZ (and in Wikipedia) for defining the terms in an equation, depending on the author. I usually list and define them below the equation. However, in this case I defined them in words (rather than math) in the first sentence preceding the equation because I don't want to get involved in explaining what "partial of T" and "partial of P" are ... or explaining thermodynamics notation.
By the way, Karl, please read the blue banner at the top of this page explaining how to use indentation on Talk pages. Afterthought: Karl, since you are an Engineering Editor, you can join David Volk in nominating this article for approval if you so wish. If you need help in doing that, contact the Approval Manager. Milton Beychok 19:00, 30 September 2009 (UTC)
Milt, actually, I did know about the indentation and purposefully did not use any indents because I was not commenting on others' comments I was starting my own comment stream about definitional notation. With the indentation as it's running now, it appears that I was commenting on the 4 bullet points and the successive responses down to the 4th level. If I've misunderstood, may apologiges for my confusion there.
On the approval, I'll go read that as I'm ready to do so for this. Karl D. Schubert 20:29, 30 September 2009 (UTC)

(unindent)Karl, when you want to start a new thread, just click on the + at the top of the page and that will automatically provide you with a pop-up for creating a new subheading. As long as we are commenting under this subheading, we should continue indenting except when it is getting too squeezed. Then just start over, as I have done here, with "(unindent)" and begin the indentation under this subheading again. No apologies are needed ... when I was new, I committed a number of sins before I learned. Regards, Milton Beychok 20:43, 30 September 2009 (UTC)


I did some copy editing and joined the approval. --Daniel Mietchen 21:59, 30 September 2009 (UTC)


Independent of this approval, I would like to see the JT data for fluorine, but couldn't find any — only this reference: Prydz, Rolf; and Straty, G. C. : PVT Measurements, Virial Coefficients, and Joule-Thomson Inversion Curve of Fluorine. J. Res. Nat. Bur. Standards, Sec. A - Phys. Chem., vol. 74A, no. 6, Nov.-Dec. 1970, pp. 747-760. If any of you have access to such data, I would appreciate it being shared here. --Daniel Mietchen 22:54, 30 September 2009 (UTC)

Sorry, Daniel, but I have no J-T data for Fluorine. Milton Beychok 04:58, 1 October 2009 (UTC)

possible approval on the 8th?

I made a couple of *tiny* changes a couple of days ago, so if I'm to Approve it tomorrow, the Editor is going to have to upgrade the version. Thanks! Hayford Peirce 22:20, 7 October 2009 (UTC)

Any of the approving editors may change the version to be approved. Since Hayford's edit doesn't even change the word order, there is no change to content, so we may safely assume the other editors also approve. If none of the editors change the version to be approved, the rules say the version cited in the template still goes through to approval. --Joe Quick 22:57, 7 October 2009 (UTC)
I updated the version number. David E. Volk 23:01, 7 October 2009 (UTC)
You also have to update the date -- that's the only thing I pay any attention to. Thanks! Hayford Peirce 23:06, 7 October 2009 (UTC)
Thanks for doing the update, David. --Daniel Mietchen 23:19, 7 October 2009 (UTC)
Hayford, you should be paying attention to the version and not the date. The version is the more important indicator of which text the editors are in favor of approving. --Joe Quick 17:12, 8 October 2009 (UTC)
It's too confusing to me. If they want me to Approve a version, I will only approve the latest version. Period. Matt apparently understands the intricacies of approving an earlier version and then sticking a link to it in the yellow strip that goes across the Talk page; I don't. So if you need an earlier version to be approved, Matt is the man, not me. Sorry. Hayford Peirce 18:06, 8 October 2009 (UTC)

(unident) Hayford, David Volk (the original nominating editor) yesterday revised the version and the date. The History of the Metadata template shows both of those revisions by David. His revised entries were October 7, 2009 and version 100584885. Nobody has made any revisions since yesterday. So what is the problem? Milton Beychok 18:39, 8 October 2009 (UTC)

I *know* he did -- there *is* no problem. At least not with this article here. But Joe was saying that *in principle* I should pay attention to the version, not the date. And *I'm* saying that I will pay attention to the date, not the version. Once again, en principe.... Hayford Peirce 18:43, 8 October 2009 (UTC)

APPROVED Version 1.0

Proposed New Material

Under the Applications heading, I would like to contribute some content on some interesting implications:

  • hydrogen can ignite itself in a bad leak
  • causes cooling of steam in turbines, a significant issue during a restart
  • it's how the common (now ubiquitous?) air conditioner works - the TX valve is where the expansion happens

Your thoughts? Graham Proud 18:43, 29 April 2011 (CDT)

Hi, Graham, glad to see you back. I have no problem with your first two items (hydrogen and steam). Go ahead and add your content about them.
But the third item about the expansion valve in a refrigeration system is not a Joule-Thomson expansion. It is an isenthalpic flash evaporation (also called an adiabatic flash evaporation) of a liquid into a vapor that causes what is called "auto-refrigeration". (See the Vapor compression refrigeration and the Flash evaporation articles.) The Joule-Thomson effect applies primarily to the expansion of gases. It does not apply to a flash evaporation. Milton Beychok 22:08, 29 April 2011 (CDT)