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

Efekt Joule'a-Thomsona pokazuje, że w układzie adiabatycznym, jeśli gaz utrzymywany pod wysokim ciśnieniem jest zmuszony do przejścia przez porowaty korek do obszaru niskiego ciśnienia, rozszerza się i zajmuje większą objętość, zmieniając swoją temperaturę, a w rezultacie energię wewnętrzną.
W tym procesie adiabatycznym zmiana energii wewnętrznej gazu musi być równa pracy wykonanej na gazie pomniejszonej o pracę wykonaną przez gaz. Przestawianie terminów pokazuje, że entalpia jest zachowana.
Zmiana temperatury pod wpływem ciśnienia przy stałej entalpii jest definiowana jako współczynnik Joule'a-Thomsona. Korzystając z twierdzenia o wzajemności i podstawiając zależność pojemności cieplnej, współczynnik Joule'a-Thomsona jest wyrażony jako pochodna cząstkowa entalpii z ciśnieniem.
Wyrażenie pochodnej cząstkowej w kategoriach entropii i użycie relacji Maxwella daje współczynnik Joule'a-Thomsona w funkcji temperatury.
Dodatnia wartość współczynnika wskazuje na chłodzenie, natomiast wartość ujemna wskazuje na nagrzewanie się gazu podczas rozprężania.
Dla gazu doskonałego współczynnik Joule'a-Thomsona wynosi zero, ponieważ jego temperatura pozostaje taka sama po przejściu do obszaru niskiego ciśnienia.

<ol>
	<li>Blundell, SJ i Blundell, KM (2010). Pojęcia w fizyce cieplnej. Wydanie drugie. Nowy Jork, USA: Oxford University Press. s. 316.</li>
	<li>Rex, A (2017). Fizyka termiczna Finna. Wydanie trzecie. Boca Raton, Floryda: CRC Press. s. 212.</li>
</ol>

efekt joule’a-thomsona

Efekt Joule'a-Thomsona, znany również jako efekt Joule'a-Kelvina, opisuje zmianę temperatury płynu, gdy jest on przepychany przez zawór lub porowaty korek, utrzymując go w izolowanym termicznie środowisku. Ten eksperyment nazywa się procesem dławienia. Jest to ważny efekt szeroko stosowany w chłodnictwie i skraplaniu gazów.

W tym eksperymencie gaz pod wysokim ciśnieniem przechodzi przez przepustnicę lub porowaty korek do obszaru o niższym ciśnieniu. Gaz rozszerza się podczas przechodzenia do obszaru niskiego ciśnienia i zajmuje objętość większą niż objętość początkowa. Praca jest wykonywana na gazie, gdy gaz jest przepychany przez przepustnicę. Jednak gdy się rozszerza, gaz wykonuje pracę nad otoczeniem. Temperatura gazu zmienia się w tym procesie; w ten sposób uzyskuje nową energię wewnętrzną. Zmiana energii wewnętrznej gazu musi być równa pracy wykonanej nad gazem pomniejszonej o pracę wykonaną przez gaz. Stwierdzono, że w tym procesie przepływu entalpia jest zachowana (izentalpia).

Zmianę temperatury gazu podczas zmniejszania ciśnienia przy stałej entalpii wyraża się współczynnikiem Joule'a-Thomsona:

<img alt="Równanie1" src="/files/ftp_upload/14174/14174_Equation_1.png" style="text-align: center; height: 42px;" />

Ponieważ temperatura gazu jest zmienna, współczynnik Joule'a-Thomsona może przyjmować dowolny znak, w zależności od tego, czy gaz ulega podgrzaniu, czy ochłodzeniu. Krzywa inwersji w płaszczyźnie T-p wyjaśnia nagrzewanie i chłodzenie gazu podczas procesu dławienia.

<img alt="Rysunek1" src="/files/ftp_upload/14174/14174_Figure_1.png" />

Krzywa inwersji oddziela obszar ogrzewania od obszaru chłodzenia. Maksima różnych izentalpów leżą na krzywej inwersji. Należy zauważyć, że izentalp to miejsce punktów końcowych różnych procesów dławienia, zaczynając od tego samego stanu początkowego. W zależności od tego, gdzie zostanie wybrany punkt początkowy i końcowy, podczas procesu dławienia można uzyskać zarówno efekt ogrzewania, jak i chłodzenia.

Współczynnik Joule’a-Thomsona wynosi zero dla gazu doskonałego, co wskazuje, że nie ma zmiany temperatury, gdy gaz doskonały przechodzi proces dławienia. Współczynnik jest ujemny dla gazów rzeczywistych w ekstremalnie wysokich i ekstremalnie niskich temperaturach.

Efekt Joule’a-Thomsona

Efekt Joule'a-Thomsona, znany również jako efekt Joule'a-Kelvina, opisuje zmianę temperatury płynu, gdy jest on przetłaczany przez zawór lub porowaty ...

Education

JoVE Core

Physics

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Unit 1

Jednostka 1

The First Law of Thermodynamics

Pierwsza zasada termodynamiki

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

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 | JoVE K12

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Gas Cooling and Heating in Throttling

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