Name: gas temperature changes in adiabatic processes
Uploaded: 2023-04-30T12:32:28.000Z
Duration: 1 min 18 s
Channel: JoVE

K12 Standards

new-york-state-science-learning-standards

New York State Science Learning Standards

High School

Physical Science

HS. Energy

HS-PS3-3.

Adiabatic Processes for an Ideal Gas

Proces termodynamiczny bez wymiany ciepła wewnątrz lub na zewnątrz systemu nazywany jest adiabatycznym.
Tak więc, zgodnie z pierwszą zasadą termodynamiki, zmiana energii wewnętrznej jest ujemna w stosunku do pracy wykonanej w procesie adiabatycznym.
Na przykład tłok przeciwpożarowy składający się z izolowanej termicznie rurki ma jeden koniec zamknięty, a drugi koniec ma ruchomy tłok. 
Jeśli mały kawałek wacika zostanie umieszczony w tubie, a tłok zostanie szybko wciśnięty w dół w temperaturze pokojowej, wacik zapali się pomimo braku ciepła. Dzieje się tak z powodu kompresji adiabatycznej.
Tutaj, w miarę zmniejszania się objętości, wykonana praca staje się ujemna, stąd wewnętrzna zmiana energii jest dodatnia, z odpowiadającym jej wzrostem temperatury gazu.
I odwrotnie, podczas otwierania butelki ze schłodzonym napojem gazowanym, gaz uwięziony w butelce ulega adiabatycznemu rozszerzaniu, co powoduje, że wykonana praca jest dodatnia.
W rezultacie energia wewnętrzna zmniejsza się wraz z odpowiednim spadkiem temperatury, kondensując odparowaną parę w widoczną chmurę.

<ol>
	<li>Young, H.D. i Freedman, R.A. (2012). Fizyka uniwersytecka z fizyką współczesną. San Francisco, Kalifornia: Pearson. Tamże, s. 640.</li>
	<li>Protokół OpenStax. (2019). Fizyka uniwersytecka Vol. 2. [Wersja internetowa]. Pobrane z <a href="https://openstax.org/books/university-physics-volume-2/pages/3-6-adiabatic-processes-for-an-ideal-gas">https://openstax.org/books/university-physics-volume-2/pages/3-6-adiabatic-processes-for-an-ideal-gas</a></li>
</ol>

procesy adiabatyczne dla gazu doskonałego

Gdy gaz doskonały jest sprężany adiabatycznie, to znaczy bez dodawania ciepła, wykonywana jest nad nim praca, a jego temperatura wzrasta. Podczas rozprężania adiabatycznego gaz działa, a jego temperatura spada. Sprężenia adiabatyczne faktycznie zachodzą w cylindrach samochodu, gdzie sprężanie mieszanki gazowo-powietrznej następuje tak szybko, że nie ma czasu, aby mieszanina wymieniła ciepło z otoczeniem. Niemniej jednak, ponieważ podczas sprężania wykonywana jest praca nad mieszaniną, jej temperatura znacznie wzrasta. W rzeczywistości wzrost temperatury może być tak duży, że mieszanina może eksplodować bez dodatku iskry. Takie eksplozje, ponieważ nie są zsynchronizowane, powodują, że samochód słabo pracuje – zwykle „stuka”. Ponieważ temperatura zapłonu rośnie wraz ze wzrostem liczby oktanowej benzyny, jednym ze sposobów rozwiązania tego problemu jest użycie benzyny o wyższej liczbie oktanowej.

Innym interesującym procesem adiabatycznym jest swobodna ekspansja gazu. Wyobraź sobie, że gaz jest zamknięty przez membranę po jednej stronie dwukomorowego, izolowanego termicznie pojemnika. Po przebiciu membrany gaz przedostaje się na pustą stronę pojemnika, przez co swobodnie się rozszerza. Gdy gaz rozpręża się „pod próżnią”, ciśnienie maleje (p = 0), gaz nie działa, a ponieważ naczynie jest izolowane termicznie, rozszerzanie jest adiabatyczne. Przy Q = 0 i W = 0 w pierwszej zasadzie, dU = 0, zatem energia wewnętrzna w początkowym i końcowym stanie równowagi wynosi to samo dotyczy darmowej ekspansji. Jeśli gaz jest idealny, energia wewnętrzna zależy tylko od temperatury. Dlatego też, gdy gaz doskonały rozszerza się swobodnie, jego temperatura się nie zmienia.

Procesy adiabatyczne dla gazu doskonałego

Kiedy gaz doskonały jest sprężany adiabatycznie, to znaczy bez dodawania ciepła, wykonuje się na nim pracę, a jego temperatura wzrasta. W ekspansji adiabatycznej ...

Education

JoVE Core

Physics

Fizyka

Unit 1

Jednostka 1

The First Law of Thermodynamics

Pierwsza zasada termodynamiki

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

gas temperature changes in adiabatic processes

Adiabatic processes change the temperature of an ideal gas without heat transfer. In an adiabatic compression, no heat is added, but work is done on the gas. That work raises the gas temperature. In an adiabatic expansion, the gas does work and its temperature drops.

A common example is the compression of a gas-air mixture inside a car engine cylinder. The compression happens so quickly that there is no time for heat to move between the mixture and its surroundings. Even so, the work done on the mixture can raise its temperature enough for it to explode without a spark. When that explosion happens at the wrong time, the engine knocks and runs poorly. Higher-octane gasoline can help because it has a higher ignition temperature.

The transcript also describes free expansion of a gas. In this case, a gas starts on one side of a thermally insulated two-compartment container. When the membrane is punctured, the gas rushes into the empty side and expands into a vacuum. Because the pressure outside is zero, the gas does no work. Since the container is thermally insulated, the process is adiabatic. With Q = 0 and W = 0, the first law gives dU = 0, so the internal energy stays the same before and after the expansion. For an ideal gas, internal energy depends only on temperature, so the temperature does not change during free expansion.

Gas Temperature Changes in Adiabatic Processes

gas-temperature-changes-in-adiabatic-processes

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adiabatic processes for an ideal gas

Adiabatic processes change the temperature of an ideal gas without heat transfer. In an adiabatic compression, no heat is added, but work is done on the gas. That work raises the gas temperature. In an adiabatic expansion, the gas does work and its temperature drops. A common example is the compression of a gas-air mixture inside a car engine cylinder. The compression happens so quickly that there is no time for heat to move between the mixture and its surroundings. Even so, the work done on...

pressure and volume in an adiabatic process

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Learn how adiabatic compression and free expansion affect an ideal gas. See why temperature rises in compression, drops in expansion, and stays the same in free expansion.

Gas Temperature Changes in Adiabatic Processes | JoVE K12

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Gas Temperature Changes in Adiabatic Processes

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