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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)
The first responder to someone's new comment should enter the response just beneath the new comment (instead of using the above + tab) and indent the response by starting with a colon like this :. Any second responder, indent further by starting with two colons like this :: and any third responder, start with three colons like this ::: and so forth. If we don't follow these practices, the result is jumbled mess.
Speaking as someone new to this topic, the "proof" seems imcomplete. After appling the first law, the proof states that it implies constant enthalpy. This seems more like a statement than a proof. Maybe it is obvious to those schooled in the art, but that article should be written for those who are not. Any chance a qualified person could add a few lines to bridsge the gap? 鈥擯receding unsigned comment added by 65.200.157.177 ( talk) 12:29, 31 October 2008 (UTC)
Enthalpy is defined as E + P V. You can rewrite the equation as
E1 + P1 V1 = E2 + P2 V2
therefore
H1 = H2
Count Iblis ( talk) 13:44, 31 October 2008 (UTC)
My initial rewrite was in a form suitable for a thermodynamics textbook. I have completely rewritten it in an attempt to make it suitable for an encyclopedia. Retired Pchem Prof ( talk) 17:31, 12 January 2016 (UTC)
I rewrote the section on "Physical mechanism". The first paragraph was OK and I left it in. The second dealt with an iso-energetic process, not an iso-enthalpic one, so I deleted much of it; what remains is in the 4th paragraph of the revised section. I deleted the 3rd and 4th paragraphs. They were confusing, unhelpful, and almost certainly wrong. I need to add links to the new text; I will do that when I figure out how. Retired Pchem Prof ( talk) 21:15, 9 January 2016 (UTC)
The article was extensively revised for a number of reasons, including:
I hope that the overall revision has resulted in a much improved article. - mbeychok 01:36, 11 June 2006 (UTC)
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.
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)
I think that perhaps you are confusing the noun heat with the verb heat. Yes, there is no heat (the noun) transferred during a Joule-Thomson expansion. But in those cases where the Joule-Thomson expansion results in raising the temperature, the gas has been heated (the verb).
I have looked in 3 different dictionaries and they all say that the verb "heat" means to make warm or hot, or become warm or hot. Raising the temperature makes the gas warmer or hotter and therefore the verb "heat" is just as appropriate as the verb "warm" ... and your statement that it is obviously inapproprate to use the verb "heat" is incorrect.
To the vast majority of people, when you raise the temperature of something you have heated (verb) that something ... whether or not you added any heat (noun) in order to raise the temperature of that something. Therefore, I am reverting your changes. Regards, mbeychok ( talk) 03:30, 11 March 2008 (UTC)
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. 鈥擯receding unsigned comment added by 91.153.151.172 ( talk) 01:00, 14 March 2008 (UTC)
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)
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
These needs to be addressed before it's considered A-Class IMO.
Headbomb {
蟿伪位魏
魏慰谓蟿蟻喂尾蟼 鈥
WP Physics}
23:13, 15 June 2008 (UTC)
Actually, there are so many inaccuracies, that it would be wiser to rewrite the article first and then look at the prose. I just corrected a few things. The most obscene statement was: "the gas does no work" which was clearly mentioned in context of the Joule-Thompson process, not the free expansion case. It almost made me sick to read that聽:( Count Iblis ( talk) 00:59, 16 June 2008 (UTC)
I've picked up my Reif (Fundamentals of Statistical and Thermal Physics). Here's what it says about:
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,
Assume that the internal energy change of the (thin-walled) container is negligibly small. Then the 螖E 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
which verifies that E(T,V) is independent of the volume V.
[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.
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 渭 > 0, in particular, the initial temperature must be less than the maximum temperature on the inversion curve....
Hope this helps Headbomb { 蟿伪位魏 魏慰谓蟿蟻喂尾蟼 鈥 WP Physics} 15:30, 17 June 2008 (UTC)
Thank's very much for typing in these texts from F. Reif's book (the best book on Statistical Mechanics ever written, b.t.w.)! Count Iblis ( talk) 15:38, 17 June 2008 (UTC)
Reif's the shit :P. Everyone hated that book back then, but it's the only thing that rescued me from the horrible teacher we had back then. And by horrible, I really do mean horrible. Stuff like you had to argue that ln(0) was not equal to 0, and that ln(1) was not equal to 1, and then when she couldn't argue anymore, she hand-waved it away "Well it's just conventions anyway" or "Well those are approximations". ln(0)=0 an approximation... Yeah... Or gave us exams problems such as "Find the density of the atmosphere as a function of height. Assume that the atmosphere is a dilute gas (i.e a gas where gravity is negligible)".
Anyway Reif is an awesome book, by far the best I've seen on statistical and classical thermodynamics. Very thorough in its treatment of concepts, and never falls back on abhorrent "obtaining this formula is trivial so it is left as an exercise to the reader"-s or the "it can be demonstrated that..."-s. Headbomb { 蟿伪位魏 魏慰谓蟿蟻喂尾蟼 鈥 WP Physics} 15:47, 17 June 2008 (UTC)
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)
Yeah, a "fairly simple article" that contained the statement: "the gas does no work" and now it just explains that if the gas moves through the valve, it will perform work and if you add to that the internal energy change and the condition that no heat has been absorbed, the enthalpy will stay the same. That's high school level physics (at least it used to be when I was in high school). The appendix is technical, but then that's why that technical stuff is delegated to the appendix. Count Iblis ( talk) 18:58, 17 June 2008 (UTC)
Articles don't have appendices. Renaming the section to "derivation of the JT coefficient" or something like that would be better. Headbomb { 蟿伪位魏 魏慰谓蟿蟻喂尾蟼 鈥 WP Physics} 20:51, 17 June 2008 (UTC)
I see! This must then also be done in these articles:
Count Iblis ( talk) 21:46, 17 June 2008 (UTC)
Yuppers. Headbomb { 蟿伪位魏 魏慰谓蟿蟻喂尾蟼 鈥 WP Physics} 01:10, 18 June 2008 (UTC)
In the first paragraph, the well-known Joule-Thomson effect which has been used for decades has suddenly been named the "throttling process".
Then the following description section starts out by describing an entirely different process ... an isentropic expansion during which work is done (such as occurs when a gas is expanded in a turbo-expander) and the temperature decreases. That is correct but it does not describe the Joule-Thomson effect which is what this article is meant to be about.
Then it discusses a "free expansion" and is linked to an incomprehensible stub of an article consisting of only three sentences.
Then it finally begins an equally tortuous discussion of the Joule-Thomson effect.
The very first two sentences should read:
The Joule-Thomson effect or Joule-Kelvin effect is the increase or decrease in the temperature of a real gas (as differentiated from an ideal gas) when it is allowed to expand freely through a valve or other throttling device while kept insulated so that no heat is transferred to or from the gas, and no external mechanical work is extracted from the gas. The Joule-Thomson effect is an isenthalpic process, meaning that the enthalpy of the gas is constant (i.e., does not change) during the expansion.
Count Iblis and Headbomb, have either of you ever heard of KISS ... meaning Keep It Simple Sam? -- Pchemist ( talk) 21:04, 1 September 2008 (UTC)Actually "KISS" stands for "Keep it simple STUPID."
Have either of you ever designed an industrial large-scale low-temperature distillation system using the J-T effect? I have designed and operated at least 5 such systems during my chemical engineering career and those systems are currently operating well.
This article was meant to simply and clearly explain what a Joule-Thomson effect is and how to use it. You might read the comment posted above by some reader on March 14th, 2008 entitled "What a wonderful article!
You two have turned an excellent, clearly written explanation of the J-T effect into a messy, tortuous thermodynamic treatise. What you have ended up with is an excellent example of the old saying: Those who can, do ... and those who cannot, teach. mbeychok ( talk) 08:12, 22 June 2008 (UTC)
Mbeychok, the reason why it was necessary to make some changes to the article was because the previous version was misleading. Now the bold faced quote is technically correct, but the old version said something like "the gas does no work" if I remember correctly, which is false if you take it literally. It is only correct if you define that work done is the work extracted from the system. But then, how is a reader, whose background may not be engineering, going to guess that work done by or on the gas does not count unless it turns a turbine if you don't mention that?
I agree that the article can be written up more clearly. However, it has to be accssible to people who are not engineers, who do not automatically "see that no turbine is extracting work" when they only read about a gas moving through a valve and no turbine is explicitely mentioned.
And is giving an explanation for why enthalpy is conserved really that complicated? It is all based on the fact that pressure times change in volume is work, which is taught in high school. How can giving that explanation have turned the article into a "tortuous thermodynamic treatise"? Perhaps you are referring to the Appendix. But then that's why that section is called "Appendix".
Oh, and didn't Einstein say that:
Everything should be made as simple as possible, but not simpler
Count Iblis ( talk) 13:23, 22 June 2008 (UTC)
The JT effect refers to the temperature drop (perhaps this was later generalized to temperature change, but originally it referred to the drop) due to a fluid's expansion when its expansion is constrained (i.e pressure difference is kept constant, a porous plug is one way of achieving this, but not the only one). Having a thermally insulated environment is an experimental and theoretical consideration to isolate the effects of heat exchange. If the environment is insulated, the process is isenthalpic, otherwise it's not. Headbomb { 蟿伪位魏 鈥 WP Physics: PotW} 15:48, 26 June 2008 (UTC)
The temperature change can be of either sign, but the JT effect is when the temperature drops. Headbomb { 蟿伪位魏 鈥 WP Physics: PotW} 16:06, 26 June 2008 (UTC)
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)
Use Castellan's Physical Chemistry as I provided it here. It's exactly there, same chapter and everything. Same thing happens for Helium, but Helium doesn't go BOOM!, so it's not dangerous. Headbomb { 蟿伪位魏 鈥 WP Physics: PotW} 17:16, 26 June 2008 (UTC)
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 { 蟿伪位魏 鈥 WP Physics: PotW} 17:24, 26 June 2008 (UTC)
Joule-Thomson expansion, the process by which a gas at constant pressure P1 is caused to flow adiabatically into a region of lower constant pressure P2 via a valve or porous plug such that P1V1 = P2V2. Since the pressures on both sides of the porous plug are each kept constant the compressive work "done on" the high pressure side of the porous plug equals the expansion work "done by" the low pressure side of the system. Accordingly the change in energy of the system equals this work. Since there is no exchange of heat with the environment (adiabatic process) the enthalpy (H = U + PV) remains constant: E2 - E1 = P1V1 - P2V2 or H2 = H1(see Appendix).
P1V1 = P2V2? Looks nonsensical to me, because that would mean that the internal energy should is constant, which is definitely not the case in the JT process (unless the gas is ideal). Count Iblis ( talk) 03:18, 3 September 2008 (UTC)
Your right. I must admitt I got involved here in haste. I saw many things that needed correction and did a patch job. Here is what should be done:
The discussion about different types of expansion should be removed because each one could be discussed more rigorously and with greater attention to accuracy. The JT effect should be carfully be framed as an expansion of a gas at constant enthalpy, period. Given that all else falls out. q = 0, energy change = work. Now you can look at the work done a lot of different ways. One way it should not be looked at is from the perspective of gas expanding from a compressed gas cylinder. It should also not be looked at from the perspective of how the JT coeficient is actually measured i.e. by measuring the isothermal JT coef. Further confounding the issues I have with Racecarr's text is that the temperatur of the gas on either side of the porous plug are not the same, but both the expansion and the compression each occur isothermally. Accordingly consider the following revision:
Joule-Thomson expansion, the process by which a gas at constant pressure P1 is caused to flow under adiabatic conditions into a region of lower constant pressure P2 via a valve or porous plug such that the enthalpy remains constant. Under such conditions (q = 0)the internal energy change is only the work done, 螖U = w. Since the pressures on both sides of the porous plug are each kept constant, the compressive work "done on" the high pressure side of the porous plug plus the expansion work "done by" the low pressure side of the system is this "total" work, w = P1V1 - P2V2. The measurement of the requisite temperature change that accompanyies this expansion is the Joule Thomson effect. The Joule Thomson effect is quantified as the ratio of this temperature change over the pressure difference found under conditions of constant enthalpy.(see Appendix). -- Pchemist ( talk) 15:29, 3 September 2008 (UTC)
is necessary. I think that you are looking at all of the gas on both sides and you want to look at a steady state situation. But that can better be mentioned explicitely, like in the current version that mentions:Since the pressures on both sides of the porous plug are each kept constant
.under steady state conditions and without change in kinetic energy
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. 鈥擯receding unsigned comment added by Trifold ( talk 鈥 contribs) 17:01, 6 September 2008 (UTC)
You're thinking of Gibbs free energy there with the H-TS. 鈥擯receding unsigned comment added by 128.61.49.68 ( talk) 06:06, 19 October 2010
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! -- 鈽 SamuelWantman 03:46, 31 March 2009 (UTC)
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)
The following section has problems:
Some points:
I removed this section, leaving the one that follows, which is unconfused, correct, and complete in itself. 鈥 Preceding unsigned comment added by 86.162.16.245 ( talk) 19:23, 3 November 2011 (UTC)
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)
A throttling process proceeds along a constant-enthalpy curve in the direction of decreasing pressure, which means that the process occurs from right to left on a Temperature-Pressure diagram.
The article continues with a detailed description of this diagram, but the displayed diagram appears to be about a mathematically analogous but different process. And it is not a temperature-pressure diagram. As a result, it is not labelled in a way that makes it the right diagram.
It would be great to have the correct diagram!
Here is a sample: [1] But where is one that can added to the article?
89.217.4.12 ( talk) 18:06, 14 March 2015 (UTC)
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)
As per #Diagram_needed. After failing to find the curve on commons and failing to use the matlab code XSteam to generate the curves, I made a generic curve. I will eventually attempt to put it into the article, unless somebody asks me not to, or unless somebody does it for me. -- Guy vandegrift ( talk) 00:24, 20 March 2015 (UTC)
FYI I did try to make a proper inversion curve using the matlab program Xsteam. Unfortunately it does not evaluate at the high temperatures and pressures required to capture the curve, if it indeed exists for water. The "hypothetical" substance is indeed water, or at least my guess as to where the inversion exists, if it even exists for water.-- Guy vandegrift ( talk) 00:46, 20 March 2015 (UTC)
I reverted an edit in Joule鈥揟homson_effect#Proof_that_the_specific_enthalpy_remains_constant because it lacks precision. I am under the impression that there is a term 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)
One option is to present the material at a bit higher level in another section. See for example section 12-3 of this article:
http://highered.mheducation.com/sites/dl/free/0073380202/903327/Sample_Chapter.pdf
The final sentence of the introduction reads "The physical mechanism associated with the Joule鈥揟homson effect is closely related to that of a shock wave". I propose to delete it since it seems to serve no purpose. Retired Pchem Prof ( talk) 17:17, 19 January 2016 (UTC)
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)
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)
The comment(s) below were originally left at Talk:Joule鈥揟homson effect/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.
I have rated the Joule-Thomson effect article as Class=A and Importance=High. I would first like to say that this article is, in my opinion, most important to Engineers and Chemists as well as to Physicists. I would not have categorized it as solely a Physics article. It is of very high importance to chemists and engineers who work in a great many industries. I have classified it as Class A because it has been well-written, organized well as per Wikipedia practice and includes an excellent Bibliography of pertinent reference texts. - mbeychok 03:05, 29 November 2006 (UTC) |
Substituted at 01:12, 22 May 2016 (UTC)
I'm writing as a unqualified learner (too old to be called a student), and I found this article less clear than it used to be.
A few years ago I read this article and it explained this effect in terms of what was happening to the atoms or molecules (attractive and repulsive forces), I thought that was a great simple and easy to grasp explanation .... and no maths needed.
So I went back to lookup that description and found it in the archived version of this article, dated 10th March 2008
Whether I'm right or wrong, I expect this to be an encyclopedia article that introduces me to what the JT Effect is and why it arises I'm tempted to put back in as the "Simple folks explanation of the Physical Mechanism" That version contains the following description under the heading "Physical Mechanism" - If it is a valid description, I think it should be added back into the article ...
As a gas expands, the average distance between molecules grows. Because of intermolecular attractive forces, expansion causes an increase in the potential energy of the gas. If no external work is extracted in the process (鈥渇ree expansion鈥) and no heat is transferred, the total energy of the gas remains the same because of the conservation of energy. The increase in potential energy thus means a decrease in kinetic energy and therefore in temperature.
A second mechanism has the opposite effect. During gas molecule collisions, kinetic energy is temporarily converted into potential energy. As the average intermolecular distance increases, there is a drop in the number of collisions per time unit, which causes a decrease in average potential energy. Again, total energy is conserved, so this leads to an increase in kinetic energy (temperature). Below the Joule-Thompson inversion temperature, the former effect (work done internally against intermolecular attractive forces) dominates, and free expansion causes a decrease in temperature. Above the inversion temperature, the latter effect (reduced collisions causing a decrease in the average potential energy) dominates, and free expansion causes a temperature increase.
I arrived at this article today when I followed a link from the CryoCoolers article, I was hoping to get a better understanding of how a JT Expansion works in the real world. 鈥斅燩receding unsigned comment added by NicholasB54 ( talk 鈥 contribs) 02:37, 15 August 2016 (UTC)
It seems it was an edit on 9th Jan 2016 by "Retired PChem Prof" that made the "Physical Mechanism" section gobbledegook for me
Just added the "How the effect arises" section from IP 78.17.95.110 reverting the 2 paragraphs I found so simple and useful 鈥斅燩receding unsigned comment added by NicholasB54 ( talk 鈥 contribs) 00:32, 29 August 2016 (UTC)
"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. 鈥斅燩receding unsigned comment added by 204.136.206.153 ( talk) 07:07, 19 October 2017 (UTC)
"In vapor-compression refrigeration, as used in common refrigerators and air conditioners, it [Joule鈥揟homson expansion] produces cooling in the throttling valve."
This technically might be* correct, but sounds like this is how vapor-compression refrigeration actually cools things.
But even for a pure gas these few bar of pressure difference would only be able to produce a delta-T of ~3K anyway, thus a irrelevant temperaturchange. I remove this somewhat missleading and potentially false sentence. 鈥斅燩receding unsigned comment added by 204.136.206.153 ( talk) 07:19, 19 October 2017 (UTC)
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)
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)