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

O efeito Joule-Thomson demonstra que, em um sistema adiabático, se um gás mantido em alta pressão é forçado a passar por um tampão poroso para uma região de baixa pressão, ele se expande e ocupa um volume maior, alterando sua temperatura e, como resultado, sua energia interna.
Nesse processo adiabático, a mudança na energia interna do gás deve ser igual ao trabalho realizado no gás menos o trabalho realizado pelo gás. Reorganizar os termos mostra que a entalpia é conservada.
A mudança de temperatura com pressão em entalpia constante é definida como o coeficiente de Joule-Thomson. Usando o teorema da reciprocidade e substituindo a relação de capacidade térmica, o coeficiente de Joule-Thomson é expresso em termos da derivada parcial da entalpia com pressão.
Expressando a derivada parcial em termos de entropia e usando a relação de Maxwell, obtém-se o coeficiente de Joule-Thomson em função da temperatura.
Um valor de coeficiente positivo indica resfriamento, enquanto um valor negativo indica aquecimento do gás durante a expansão.
Para um gás ideal, o coeficiente de Joule-Thomson é zero, pois sua temperatura permanece a mesma ao passar para a região de baixa pressão.

<ol>
	<li>Blundell, S.J. e Blundell, K.M. (2010). Conceitos em Física Térmica. Segunda edição. Nova York, EUA: Oxford University Press. pp. 316.</li>
	<li>Rex, A (2017). Física Térmica de Finn. Terceira edição. Boca Raton, FL: CRC Press. Pp. 212.</li>
</ol>

efeito joule-thomson

O efeito Joule-Thomson, também conhecido como efeito Joule-Kelvin, descreve a mudança de temperatura de um fluido quando ele é forçado através de uma válvula ou plug poroso, enquanto mantido em um ambiente termicamente isolado. Este experimento é chamado de processo de estrangulamento. Este é um efeito importante amplamente utilizado em refrigeração e liquefação de gases.

Este experimento força um gás de alta pressão através de uma válvula de estrangulamento, ou um plug poroso, para uma região de baixa pressão. O gás se expande à medida que passa para a região de baixa pressão e ocupa um volume maior que o volume inicial. Trabalho é realizado no gás quando ele é forçado através de uma válvula de estrangulamento. No entanto, quando se expande, o gás realiza trabalho sobre o ambiente. A temperatura do gás varia nesse processo; portanto, ele adquire uma nova energia interna. A mudança na energia interna do gás deve ser igual ao trabalho realizado sobre o gás menos o trabalho realizado pelo gás. Verifica-se que a entalpia é conservada (isentálpica) nesse processo de fluxo.

A mudança de temperatura do gás quando a pressão é reduzida em entalpia constante é dada pelo coeficiente de Joule-Thomson:

<img alt="Equation1" src="/files/ftp_upload/14174/14174_Equation_1.png" style="text-align: center; height: 42px;" />

Desde que a temperatura do gás varie, o coeficiente de Joule-Thomson pode assumir qualquer sinal, dependendo se o gás se aquece ou se resfria. A curva de inversão no plano T-p explica o aquecimento e resfriamento do gás durante o processo de estrangulamento.

<img alt="Figure1" src="/files/ftp_upload/14174/14174_Figure_1.png" />

A curva de inversão separa a região de aquecimento da região de resfriamento. Os máximos das diferentes isentálpicas estão localizados na curva de inversão. Observe que uma isentálpica é o conjunto dos pontos finais de diferentes processos de estrangulamento, a partir do mesmo estado inicial. Dependendo de onde os pontos inicial e final são escolhidos, tanto os efeitos de aquecimento quanto de resfriamento podem ser produzidos durante o processo de estrangulamento.

O coeficiente de Joule-Thomson é zero para um gás ideal, indicando que não há mudança de temperatura quando um gás ideal passa por um processo de estrangulamento. O coeficiente é negativo para gases reais em temperaturas extremamente altas e extremamente baixas.

Efeito Joule-Thomson

O efeito Joule-Thomson, também conhecido como efeito Joule-Kelvin, descreve a mudança de temperatura de um fluido quando ele é forçado através de uma válvula ou ...

Education

JoVE Core

Physics

Física

Unit 1

Unidade 1

The First Law of Thermodynamics

A Primeira Lei da Termodinâmica

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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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