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

Der Joule-Thomson-Effekt zeigt, dass sich ein Gas, das unter hohem Druck gehalten wird, ausdehnt und ein größeres Volumen einnimmt, wenn es in einem adiabatischen System gezwungen wird, durch einen porösen Pfropfen in einen Niederdruckbereich zu gelangen, wodurch sich seine Temperatur und damit seine innere Energie ändert.
Bei diesem adiabatischen Prozess muss die Änderung der inneren Energie des Gases gleich der Arbeit sein, die am Gas geleistet wird, abzüglich der Arbeit, die das Gas leistet. Die Neuanordnung der Terme zeigt, dass die Enthalpie erhalten bleibt.
Die Änderung der Temperatur mit dem Druck bei konstanter Enthalpie ist definiert als der Joule-Thomson-Koeffizient. Unter Verwendung des Reziprozitätssatzes und der Substitution der Wärmekapazitätsrelation wird der Joule-Thomson-Koeffizient als partielle Ableitung der Enthalpie mit dem Druck ausgedrückt.
Wenn man die partielle Ableitung in Form der Entropie ausdrückt und die Maxwell-Beziehung verwendet, erhält man den Joule-Thomson-Koeffizienten als Funktion der Temperatur.
Ein positiver Koeffizient zeigt die Abkühlung an, während ein negativer Wert die Erwärmung des Gases während der Expansion anzeigt.
Für ein ideales Gas ist der Joule-Thomson-Koeffizient Null, da seine Temperatur beim Übergang in den Tiefdruckbereich gleich bleibt.

<ol>
	<li>Blundell, S.J. und Blundell, K.M. (2010). Konzepte der thermischen Physik. Zweite Auflage. New York, USA: Oxford University Press. S. 316.</li>
	<li>Rex, A (2017). Finns thermische Physik. Dritte Auflage. Boca Raton, FL: CRC Press. S. 212.</li>
</ol>

joule-thomson-effekt

Der Joule-Thomson-Effekt, auch als Joule-Kelvin-Effekt bekannt, beschreibt die Temperaturänderung eines Fluids, wenn es durch ein Ventil oder ein poröses Rohr gezwungen wird, während es in einer thermisch isolierten Umgebung gehalten wird. Dieses Experiment wird als Drosselungsprozess bezeichnet. Dies ist ein wichtiger Effekt, der in der Kälte- und Gasverflüssigung weit verbreitet ist.

Bei diesem Experiment wird ein Gas mit hohem Druck durch ein Drosselventil oder ein poröses Rohr in eine Region mit niedrigem Druck geführt. Das Gas erweitert sich, während es durch die Region mit niedrigem Druck strömt und nimmt dabei ein Volumen ein, das größer ist als das anfängliche Volumen. Wird das Gas durch ein Drosselventil gezwungen, dann wird Arbeit an ihm verrichtet. Wenn es sich jedoch ausdehnt, verrichtet das Gas Arbeit an der Umgebung. Die Temperatur des Gases variiert in diesem Prozess; daher erreicht es eine neue innere Energie. Die Änderung der inneren Energie des Gases muss der am Gas verrichteten Arbeit minus der vom Gas verrichteten Arbeit entsprechen. Es wird festgestellt, dass die Enthalpie bei diesem Fließprozess erhalten bleibt (isenthalpisch).

Die Temperaturänderung des Gases bei Druckreduzierung und konstanter Enthalpie wird durch den Joule-Thomson-Koeffizienten angegeben:

<img alt="Equation1" src="/files/ftp_upload/14174/14174_Equation_1.png" style="text-align: center; height: 42px;" />

Da sich die Temperatur des Gases ändert, kann der Joule-Thomson-Koeffizient sowohl positive als auch negative Werte annehmen, je nachdem, ob das Gas erhitzt oder gekühlt wird. Die Umkehrkurve in der T-p-Ebene erklärt die Erwärmung und Abkühlung des Gases während des Drosselungsprozesses.

<img alt="Figure1" src="/files/ftp_upload/14174/14174_Figure_1.png" />

Die Umkehrkurve trennt den Bereich der Erwärmung vom Bereich der Abkühlung. Die Maxima der verschiedenen Isenthalpen liegen auf der Umkehrkurve. Beachten Sie, dass eine Isenthalpe die Bahn der Endpunkte verschiedener Drosselungsprozesse ist, die bei demselben Anfangszustand beginnen. Abhängig davon, wo die Anfangs- und Endpunkte gewählt werden, können sowohl Erwärmungs- als auch Kühlungseffekte während des Drosselungsprozesses auftreten.

Der Joule-Thomson-Koeffizient ist für ein ideales Gas null, was bedeutet, dass keine Temperaturänderung auftritt, wenn ein ideales Gas einen Drosselungsprozess durchläuft. Der Koeffizient ist für reale Gase bei extrem hohen und extrem niedrigen Temperaturen negativ.

Joule-Thomson-Effekt

Der Joule-Thomson-Effekt, auch bekannt als Joule-Kelvin-Effekt, beschreibt die Temperaturänderung eines Fluids, wenn es durch ein Ventil oder poröse ...

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The First Law of Thermodynamics

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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.

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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 | JoVE K12

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Gas Cooling and Heating in Throttling

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