Talk:Joule–Thomson effect

message: Why is there no citation of the paper which described the effect originally?  It is mentioned in the beginning of the article but not cited. I think the paper may have been: "On the Thermal Effects experienced by Air in rushing through small Apertures" published to The London, Edinburgh and Dublin Philosophical Magazine, Ser, 1852.  Perhaps someone more motivated than I could find either a full text or an ISBN number for the magazine. 128.210.192.31 (talk) 19:19, 14 September 2008 (UTC)
replies: text: I don't really see any  connection between this article on the Joule-Thomson effect and your Hydrogen WikiProject.  But, to each his own I guess. - mbeychok 23:08, 4 September 2006 (UTC)
thread_title: Comments

message: Hello folks.  This is a nice article, but shouldn't it have some link to the general article on refrigeration?  After all, that is what the Joule-Thomson effect is used for in practice.  Thanks.
:You're right, it does need a link so I added it in the "See also" section. In the future, PLEASE provide a heading for your discussions (which I added for you) and also sign with your name and the date. Thanks, mbeychok 08:12, 17 November 2006 (UTC)
replies: text:  What it really needs is a link to an article on the Linde process. But it seem there is no such article, and I am not qualified to write it. Retired Pchem Prof (talk) 17:29, 19 January 2016 (UTC)
replies: text:  Turns out there is an article on the Linde process, but using a name I never heard before (Hampson–Linde cycle). I put that link in, along with some other refrigeration related links. Retired Pchem Prof (talk) 15:25, 2 February 2016 (UTC)
replies: text: User:Tevildo has kindly created two new titles: Linde process and Linde cycle. (They both lead the reader to the article on the Hampson-Linde cycle.) Dolphin (t) 09:41, 11 February 2016 (UTC)
replies: text: Thanks for the mention!  Just a question of converting a couple of piped links to proper redirects. Tevildo (talk) 19:13, 11 February 2016 (UTC)
thread_title: Need link to [[Refrigeration]]

message: The Joule-Thomson effect applies primarily to non-ideal real gases. To a great many people, the word "fluid" means a liquid (rather than a real gas) and therefore I felt that it should be deleted so as not to mislead many people. - mbeychok 16:11, 1 May 2007 (UTC)
thread_title:  Why the word "fluid" added by [[User:213.84.69.4]] was deleted 

message: Usually people just read various WikiPedia articles, and some are OK, others are meh, and when they read a masterpiece like this, they are happy but noone bothers to comment. Well, I decided this one was GREAT and wanted to give props to the author(s). The pedagogic methodology exhibited here is of the finest quality. I wish I knew what other material the author(s) has/have contributed. If anyone who reads this knows the author(s), please kindly extend my compliments.  —Preceding unsigned comment added by 91.153.151.172 (talk) 01:00, 14 March 2008 (UTC)
replies: text: Thanks for the kind words. Read my user page at User:Mbeychok to learn more about me. mbeychok (talk) 02:35, 14 March 2008 (UTC)
thread_title: What a wonderful article!

message: I fixed the typography, them moved the article again, to use the en dash to clarify the Joule and Thomson are two equal names joined, as opposed to a compound last name, which would use a hyphen.  This is how it appears in carefully edited book (like this and this and this), but like most such subtleties, it probably appears wrong more often than right.  Does anyone think this is not the best way to do it?  Dicklyon (talk) 20:32, 15 March 2008 (UTC)
replies: text: I have reverted the changes to the article, but not the move.  There was at least one typo introduced, a missing letter I think, and a bunch of unnecessary blank space added.  The title should probably either be changed back, or the hyphens should be changed back to dashes (but without reintroducing the typos).  As I indicated in the edit summary, I don't have a strong preference, but a quick web search definitely seems to turn up far more hyphens than dashes. Rracecarr (talk) 20:54, 16 March 2008 (UTC)
replies: text: Sorry about the dropped letter typo; fixed.  It's good that you don't care about the typography, as that means it will OK to do it correctly.  And I already stated that it is more commonly done wrong than right, but that's not a good reason to avoid the useful cue that doing it right provides to literate readers.  You are correct that blank lines before paragraphs are not always necessary, but they are always allowed, and make it much easier to spot headings when editing. Dicklyon (talk) 21:31, 16 March 2008 (UTC)
replies: text: Looks ok to me... Rracecarr (talk) 23:26, 16 March 2008 (UTC)
thread_title:  typography 

message: This one is much better than Henry's Law, so list won't be as long. I won't relist the FA criteria, other than mention an A class articles should be of Feature-quality (and by I mean as good as it can be, not whether or not it could achieve FA status).
The things that are missing before it can be considered A-Class
* An engaging lead, with perhaps a few historical details such as time of discovery, typical occurrences of JT Effect (and which fields uses it and to what end)
* Fix appearance problems.
:* Some sections seems to be in written in bullet "list" format, without being bullet lists (especially "Description").
:* Useless words (on the other hand), and prose (Expanded in this manner, though the temperature of an ideal gas would remain constant, the temperature of a real gas may either increase or decrease, depending on the initial temperature and pressure.). Rewrite things so there's less going through loops to figure out what the sentence means. This is not a book by Nathaniel Hawthorne :P.
:* Heavy use of jargon, wikilink things such as "enthalpy".
:* A picture would add a little something to this article. I think the section Physical mechanism is the one that would benefit from one. Not a show stopper if there isn't one tho.
:* <math> seems overkill for complexity of the things written in the table.
:* Consider centering tables within the page.
* The "flow" could be improved. Many sections feels like simple stubs (although not as much as in Henry's Law), and a collection of stubs does not make an A-class articles.
* Some sections are unreferenced. Namely:
:* Physical mechanism
:* Applications
These needs to be addressed before it's considered A-Class IMO. Headbomb {ταλκκοντριβς – WP Physics} 23:13, 15 June 2008 (UTC)
thread_title:  Reasons for B class 

message: I've picked up my Reif (Fundamentals of Statistical and Thermal Physics). Here's what it says about:
* "Free expansion experiment":
The fact that the internal energy E of a gas does not depend on its volume (if the gas is sufficiently dilute that it can be considered ideal) was verified in a classical experiment by Joule [where] he made use of the "free expansion" of an ideal gas.A container consisting of two compartments separated by a valve is immersed in water. Initially, the valve is closed, and one compartment is filled with the gas under investigation, while the other is evacuated. Suppose that the valve is now opened so that the gas is free to expand and fill both compartments. In this process no works gets done by the system consisting of the gas and container. (The container walls are rigid and nothing moves.) Hence one can say, by the first law [of thermodynamics], that the heat Q absorbed by this system equals its increase in thermal energy,
:Q=\Delta E
Assume that the internal energy change of the (thin-walled) container is negligibly small. Then the ΔE measures simply the energy change of the gas. Joule found that the temperature of the water did not change in this experiment. (Because of the large heat capacity of the water, any anticipated temperature change is, however, quite small; Joule's actual sensitivity of temperature measurement was, in retrospect, rather inadequate.) Thus the water absorbed no heat from the gas; consequently, the heat Q absorbed by the gas also vanished. All that happens in the experiment is that the temperature of the gas remains unchanged while its volume changes from its initial value Vi to its final value Vf. Since Q = 0, Joule's experiment leads [...] to the conclusion
:E(T,V_f)-E(T,V_i)=0
which verifies that E(T,V) is independent of the volume V.
*Throttling (or Joule-Thomson) Process (selective quoting): 
[Long description of the experiment]...
In this process, the mass of the gas also does work ... but no heat is absorbed ... we arrive at the result that in a throttling process the gas passes through the constriction in such a way that its enthalpy remains constant.The difference [with the free expansion] is that the gas does work in the throttling process, so that the enthalpy rather than the internal energy is the quantity that is conserved. 
* Joule-Thomson effect (withing the JT process section):
The Joule-Thomson effect constitutes a practical method for cooling gases and is often used in processes designed to liquefy gases. In order to achieve a lower temperature as a result of throttling a gas, it is necessary to work in that region of pressure and temperature where μ > 0, in particular, the initial temperature must be less than the maximum temperature on the inversion curve.... 
Hope this helps Headbomb {ταλκκοντριβς – WP Physics} 15:30, 17 June 2008 (UTC)
thread_title:  Feedback for the Isenthalic Joule-Thompson throttling proccess or whatever. 

message: I want to congratulate those who have succeeded in revising a fairly simple article about the Joule-Thomson effect into an extensive thermodynamic thesis. I am removing this article from my watchlist. It is not worth watching any more. - mbeychok (talk) 18:28, 17 June 2008 (UTC)
thread_title: Congratulations!!

message: Articles don't have appendices. Renaming the section to "derivation of the JT coefficient" or something like that would be better. Headbomb {ταλκκοντριβς – WP Physics} 20:51, 17 June 2008 (UTC)
replies: text: I've fixed it here. -- ☑ SamuelWantman 03:53, 31 March 2009 (UTC)
thread_title:  Appendix 

message: I remember reading somewhere that storage of hydrogen under pressure at room temperature is dangerous because the inversion temperature of hydrogen is below room temperature. In case of a leak (hydrogen can leak more easily than other gasses), the hydrogen that escapes will get an increased temperature causing it to burn, which may cause the entire storage vessel to rupture and explode.
The wiki article on hydrogen storage does not mention this. Perhaps if we find some source we can mention this here.
Count Iblis (talk) 16:42, 26 June 2008 (UTC)
replies: text: The Joule-Thompson heating of H2 is only a few degrees; not nearly enough to ignite it. Storing H2 is potentially dangerous because if it leaks and mixes with air there are any number of things that can make it go boom. Retired Pchem Prof (talk) 17:25, 19 January 2016 (UTC)
thread_title:  Storage of hydrogen 

message: The partial derivative of T w.r.t. P at constant H can be computed by  expressing the differential of the enthalpy dH in terms of dT and dP, and equating the resulting expression to zero and solving for the ratio of dT and dP.
What? Headbomb {ταλκ – WP Physics: PotW} 17:24, 26 June 2008 (UTC)
replies: text: With Respect To? Rracecarr (talk) 17:51, 26 June 2008 (UTC)

text: Oh... yeah that was a brain fart. Nonetheless it should be written in full. Headbomb {ταλκ – WP Physics: PotW} 18:31, 26 June 2008 (UTC)
replies: text: Agree.Rracecarr (talk) 18:49, 26 June 2008 (UTC)
thread_title:  T w.r.t. P 

message: I dissagree with description in the section Physical mechanism. Energy of gas is not constant (enthalpy is constant), process is irreversible so entrophy increases E=H-TS, energy increases below and decreases above inversion point.  —Preceding unsigned comment added by Trifold (talk • contribs) 17:01, 6 September 2008 (UTC)
thread_title:  Section Physical mechanism 

message: The article says, "During gas molecule collisions, kinetic energy is temporarily converted into potential energy."  This is not linked to any other article, and an explanation of how this happens is not obvious to me or my partner  (I went to MIT and he went to CalTech).  Our best guess for the meaning of this sentence is that for a brief instant, when they are changing direction, the particles have no velocity and thus no kinetic energy.  If we are correct, this should be added to the description, with links.  Please remember that these articles should be written for people who don't know much about the topic! -- ☑ SamuelWantman 03:46, 31 March 2009 (UTC)
replies: text: That's basically right--think of a mass bouncing off one end of a spring, the other end of which is fixed.  As it moves toward the spring, the mass has a certain amount of kinetic energy.  The spring compresses, momentarily bringing the mass to a stop.  The kinetic energy has been converted into potential energy.  Then the spring accelerates the ball (in the opposite direction) converting the potential energy back to kinetic.  The exact same thing happens in a collision between gas molecules, except that the intermolecular force is provided by Coulomb repulsion, rather than a spring. Rracecarr (talk) 04:09, 31 March 2009 (UTC)
thread_title:  Please explain 

message: As I always learned it, enthalpy is the same before and after the throttling process, but cannot be described during it due to gas passing through non-equilibrium states, the article presents it differently claiming that enthalpy is constant throughout the process. Either my memory or the article should really be updated to reflect the truth.128.61.49.68 (talk) 05:59, 19 October 2010 (UTC)
thread_title:  non-equilibrium 

message: This article is poorly written. Consider the following sentence. "In the Joule experiment, the gas expands in a vacuum and the temperature drop of the system is zero, if the gas were ideal." This illiterate phrase demonstrates a lack of coherent thought. Now consider a revised version. "An ideal gas will exhibit no change in temperature as it expands in a vacuum." Or since an ideal gas is a theoretical concept. "In Joule's analysis, an ideal gas will exhibit no change in temperature as it expands in a vacuum." The fact that real world behavior differs and why it differs should be introduced immediately after Joule's analysis of the ideal gas. Presenting the math to quantify the effect before mentioning why the effect occurs is nonsensical and abusive to the reader.184.45.118.21 (talk) 19:44, 29 June 2013 (UTC)
thread_title:  Poorly written article 

message: The subsection "Thermodynamic Interpretation of the experiment" is inconclusive. It starts to set up the thermodynamic model, then just stops. What gives??
178.38.75.27 (talk) 02:27, 15 March 2015 (UTC)
replies: text: Welcome to Wikipedia.--Guy vandegrift (talk) 14:52, 15 March 2015 (UTC)
thread_title:  Hanging subsection "Thermodynamic Interpretation of the experiment" 

message: I reverted an edit in Joule–Thomson_effect#Proof_that_the_specific_enthalpy_remains_constant because it lacks precision.  I am under the impression that there is a term \frac 1 2 \rho v^2 on each side of the equation.  If that is true, we neglect fluid kinetic energy either because it is small, or because the flow rate is the same on each side.  The fluid does accelerate and decelerate through the plug.  I agree that something needs to be said, if what is said is both accurate and brief -- the editor should try to rephrase.--Guy vandegrift (talk) 23:06, 4 April 2015 (UTC)
thread_title:  Proof that the specific enthalpy remains constant: fluid kinetic energy 

message: This derivation is not very clear. How did he get from the 2nd equation to the 3rd? I am in the process of rewriting it, following the standard textbook approach via the isothermal Joult-Thomson coefficient. It seems that some people don't like seeing math, but I see no harm as long as it is near the end. But it ought to be clear and correct. Retired Pchem Prof (talk) 20:44, 19 January 2016 (UTC)
replies: text:  I have prepared a draft rewrite of this section. It is now on my user page for comment.Retired Pchem Prof (talk) 01:36, 20 January 2016 (UTC)
replies: text: I see your draft re-write at User:Retired Pchem Prof/sandbox02#Derivation of the Joule–Thomson coefficient. This is a commendable piece of work! I will examine it closely over the next day or two and give you my comments. Dolphin (t) 07:08, 20 January 2016 (UTC)
replies: text:  I have now replaced the original section with my rewrite. Retired Pchem Prof (talk) 20:22, 28 January 2016 (UTC)
thread_title: Derivation of the Joule–Thomson (Kelvin) coefficient

message: Under "Description", I made minor edits to the 2nd and 3rd bullet points. I replaced the figure, which was not the correct one to use, as noted above under #Diagram needed and #New image: T vs P with coutours of h for inversion curve. I kept the figure simple, without the isenthalpic curves, which have so little curvature that the maxima can not really be seen. I also replaced the accompanying text, which was confusing and contained some errors. I removed the last paragraph and incorporated some of the content into the section on "Applications" along with some other minor edits. I largely rewrote the section on "Physical mechanism" to tighten up the text, make the style more suitable to an encyclopedia, remove some material that belonged in the article on Joule expansion, and included more references. Retired Pchem Prof (talk) 19:34, 1 February 2016 (UTC)
thread_title:  Changes to Description, Physical Mechanism, and Applications 

message: Substituted at 01:12, 22 May 2016 (UTC)
thread_title: Assessment comment

message: "No external work is extracted from the gas during the expansion (the gas must not be expanded through a turbine, for example)."
But isnt this exactly how its done today (turbine) and also why they couldnt liquify Helium due to the friction in the valve (unused energy remaining in the gas)?! This needs to be backed up as it contradicts how this process is actually carried out (much more efficiently) today.  — Preceding unsigned comment added by 204.136.206.153 (talk) 07:07, 19 October 2017 (UTC)
thread_title:  "gas must not be expanded through a turbine" 

message: There are many posts on Stack Exchange and elsewhere that provide maths proporting to show that and ideal gas cools on expansion, heats on compression.  Seemed odd to me, and this article confirms it.  
Further, the article resists the normal Wikipedia tradition of starting with impenetrable differential equations, but is written in an encyclopedic style and is quite intelligible to a non-expert.  Well done indeed.
It would be good to put prominent links to this in many other places. Tuntable (talk) 07:55, 29 June 2020 (UTC)
thread_title:  Excellent article 

message: For air, at 300K, it says about 0.4 K/Bar.
But when I use a bicycle pump, pumping to maybe 2 bars, the air temperature goes up by a lot more than 1 K.  Tuntable (talk) 00:30, 30 June 2020 (UTC)
replies: text: The article in general, and Fig 1 in particular, address a process that takes place with constant enthalpy. Compressing a gas in a machine such as a bike pump doesn’t take place with constant enthalpy; a simple way of examining this kind of compression is to assume it takes place with constant entropy. I think that will go some way to explaining the problem you have described. Dolphin (t) 01:35, 30 June 2020 (UTC)
thread_title:  Graph of coefficients in fig 1 looks wrong