Name: gas cooling and heating in throttling
Uploaded: 2025-05-22T09:05:59.000Z
Duration: 1 min 21 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Physical Science

SC.912.P.10

SC.912.P.10.2

Joule-Thomson Effect

L'effet Joule-Thomson démontre que dans un système adiabatique, si un gaz maintenu à haute pression est forcé de passer à travers un bouchon poreux dans une région de basse pression, il se dilate et occupe un plus grand volume, modifiant sa température et, par conséquent, son énergie interne.
Dans ce processus adiabatique, la variation de l’énergie interne du gaz doit être égale au travail effectué sur le gaz moins le travail effectué par le gaz. La réorganisation des termes montre que l’enthalpie est conservée.
La variation de température avec la pression à enthalpie constante est définie par le coefficient de Joule-Thomson. En utilisant le théorème de réciprocité et la relation de capacité thermique de substitution, le coefficient de Joule-Thomson est exprimé en fonction de la dérivée partielle de l’enthalpie avec pression.
En exprimant la dérivée partielle en termes d'entropie et en utilisant la relation de Maxwell, on obtient le coefficient de Joule-Thomson en fonction de la température.
Une valeur de coefficient positive indique un refroidissement, tandis qu’une valeur négative indique un chauffage du gaz pendant la détente.
Pour un gaz parfait, le coefficient de Joule-Thomson est nul car sa température reste la même lors du passage dans la région de basse pression.

<ol>
	<li>Blundell, S.J. et Blundell, K.M. (2010). Concepts en physique thermique. Deuxième édition. New York, États-Unis : Oxford University Press. p. 316.</li>
	<li>Rex, A (2017). Physique thermique de Finn. Troisième édition. Boca Raton, Floride : CRC Press. pp. 212.</li>
</ol>

effet joule-thomson

L'effet Joule-Thomson, également connu sous le nom d'effet Joule-Kelvin, décrit la variation de température d'un fluide lorsqu'il est forcé à travers une valve ou un tampon poreux tout en le maintenant dans un environnement thermiquement isolé. Cette expérience est appelée un processus d'étranglement. Il s'agit d'un effet important largement utilisé dans la réfrigération et la liquéfaction des gaz.

Cette expérience force un gaz à haute pression à travers une valve de restriction ou un tampon poreux vers une région de basse pression. Le gaz se dilate lorsqu'il traverse vers la région de basse pression et occupe un volume plus grand que le volume initial. Du travail est effectué sur le gaz lorsque le gaz est forcé à travers une valve de restriction. Cependant, lorsqu'il se dilate, le gaz effectue un travail sur l'environnement. La température du gaz varie dans ce processus ; par conséquent, il atteint une nouvelle énergie interne. La variation de l'énergie interne du gaz doit être égale au travail effectué sur le gaz moins le travail effectué par le gaz. On constate que l'enthalpie est conservée (isenthalpique) dans ce processus d'écoulement.

La variation de température du gaz lorsque la pression est réduite à enthalpie constante est donnée par le coefficient de Joule-Thomson :

<img alt="Equation1" src="/files/ftp_upload/14174/14174_Equation_1.png" style="text-align: center; height: 42px;" />

Étant donné que la température du gaz varie, le coefficient de Joule-Thomson peut prendre un signe quelconque, selon que le gaz se réchauffe ou se refroidit. La courbe d'inversion dans le plan T-p explique le chauffage et le refroidissement du gaz pendant le processus d'étranglement.

<img alt="Figure1" src="/files/ftp_upload/14174/14174_Figure_1.png" />

La courbe d'inversion sépare la région de chauffage de la région de refroidissement. Les maxima des différents isenthalpes se trouvent sur la courbe d'inversion. Notez qu'un isenthalpe est le lieu des points finaux de différents processus d'étranglement, à partir du même état initial. Selon l'emplacement des points initial et final, à la fois des effets de chauffage et de refroidissement peuvent être produits pendant le processus d'étranglement.

Le coefficient de Joule-Thomson est nul pour un gaz idéal, ce qui indique qu'il n'y a pas de changement de température lorsqu'un gaz idéal subit un processus d'étranglement. Le coefficient est négatif pour les gaz réels à des températures extrêmement élevées et extrêmement basses.

Effet Joule-Thomson

L’effet Joule-Thomson, également connu sous le nom d’effet Joule-Kelvin, décrit le changement de température d’un fluide lorsqu’il est forcé à travers une soupape ou un ...

Education

Enseignement

JoVE Core

Physics

Physique

Unit 1

Unité 1

The First Law of Thermodynamics

Le premier principe de la thermodynamique

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

gas cooling and heating in throttling

Gas cooling and heating in throttling is explained by the Joule-Thomson effect, also called the Joule-Kelvin effect. It describes how a fluid changes temperature when it passes through a valve or porous plug in a thermally insulated system. This type of flow is called a throttling process.

In the experiment, a high-pressure gas is forced through a throttle valve or porous plug into a lower-pressure region. The gas expands as it moves into the larger volume. Work is done on the gas as it is pushed through the valve. After expansion, the gas also does work on the surroundings.

Because the temperature changes during the process, the gas reaches a new internal energy state. The change in internal energy equals the work done on the gas minus the work done by the gas. In this flow process, enthalpy stays constant, so the process is isenthalpic. The Joule-Thomson coefficient gives the temperature change when pressure drops at constant enthalpy.

The gas may either warm up or cool down, so the Joule-Thomson coefficient can be positive or negative. The inversion curve on a temperature-pressure diagram shows where heating changes to cooling. It separates the heating region from the cooling region, and the peaks of different isenthalps lie on this curve. An isenthalp is the set of end points for throttling processes that start from the same initial state.

Depending on the starting and ending points, throttling can produce either heating or cooling. For an ideal gas, the Joule-Thomson coefficient is zero, so no temperature change occurs during throttling. For real gases, the coefficient is negative at extremely high and extremely low temperatures. This effect is important in refrigeration and in the liquefaction of gases.

Gas Cooling and Heating in Throttling

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Gas cooling and heating in throttling is explained by the Joule-Thomson effect, also called the Joule-Kelvin effect. It describes how a fluid changes temperature when it passes through a valve or porous plug in a thermally insulated system. This type of flow is called a throttling process. In the experiment, a high-pressure gas is forced through a throttle valve or porous plug into a lower-pressure region. The gas expands as it moves into the larger volume. Work is done on the gas as it is...

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Gas Cooling and Heating in Throttling

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