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  • If you've ever used a can of compressed air (also called a gas duster), to, say, clean

    如果你曾經使用過一罐壓縮空氣(也稱為氣體吸塵器),例如,清潔

  • crumbs out of your computer keyboard , you're probably aware that after a little while,

    在你的電腦鍵盤上的麵包屑 ,你可能意識到,過了一小會兒。

  • the air coming out of the can and even the can itself get really really cold.

    從罐子裡出來的空氣,甚至罐子本身也變得非常非常冷。

  • Like, cold enough they put frostbite warnings on the can!

    就像,冷到他們在罐子上貼上凍傷的警告!

  • And for good reason!

    而且理由充分!

  • It's tempting to think that compressed air cans get cold because when the gas comes out

    人們很容易認為壓縮空氣罐會變冷,因為當氣體出來時

  • of the can it expands and thus cools off.

    它在罐子裡會膨脹,從而冷卻下來。

  • But that's not exactly right - whether an expanding gas gets hotter or colder (and how

    但這並不完全正確--膨脹的氣體是變得更熱還是更冷(以及如何

  • much hotter or colder it gets) depends on the exact manner in which the gas expands.

    它變得更熱或更冷)取決於氣體膨脹的確切方式。

  • And if we apply the relevant equation fornormalgas expansion , we predict that

    而如果我們應用 "正常 "氣體膨脹的相關方程式,我們預測

  • the gas inside the compressed air can should drop from room temperature to around 100 degrees

    壓縮空氣罐內的氣體應從室溫降至100度左右

  • celsius below zero , which is, um, WAY colder than what comes out of a compressed air can.

    攝氏零度以下,嗯,比壓縮空氣罐裡出來的東西要冷得多。

  • So the gas can't be expanding in the normal way gases expand.

    所以氣體不可能以正常的氣體膨脹方式進行膨脹。

  • . And here's why: that would be like cutting the top off the can and letting the gas expand

    .這就是原因:這就像把罐頭切掉,讓氣體膨脹。

  • freely in all directions.

    在所有的方向上自由移動。

  • But the gas is actually being squeezed out through a tiny valve.

    但氣體實際上是通過一個微小的閥門被擠出來的。

  • This difference is key; the gas passing through a valve isn't simply expanding - it's

    這一區別是關鍵;通過閥門的氣體並不是簡單的膨脹--它是

  • also being pushed through by the rest of the gas behind it!

    也被它後面的其他氣體推過!

  • And that compression from behind gives the gas enough heat energy to essentially counteract

    而這種來自背後的壓縮給了氣體足夠的熱能,基本上可以抵消

  • the cooling from expansion.

    膨脹帶來的冷卻。

  • In terms of the gas law, this means the volume goes up by the same factor that the pressure

    就氣體定律而言,這意味著體積上升的因素與壓力上升的因素相同。

  • goes down, so pressure times volume is pretty much constant and the temperature stays about

    下降,所以壓力乘以體積是基本恆定的,溫度保持在大約

  • constant.

    恆定。

  • But not exactly - most gases at room temperature do get slightly colder when passing through

    但並不完全如此--大多數室溫下的氣體在通過時確實會略微變冷。

  • a valve . A good demo of this is to let the air out of a bike tire; the valve gets colder

    一個閥門。一個很好的例子是把自行車輪胎的空氣放出來;閥門會變冷。

  • , but not crazy cold.

    ,但不是瘋狂的寒冷。

  • Similarly, the gas leaving a can of compressed air cools a little bit passing through the

    同樣地,離開壓縮空氣罐的氣體經過以下幾個方面的冷卻

  • nozzle . But this can't be the only contributor to the cooling.

    噴嘴。但這不可能是造成冷卻的唯一因素。

  • I mean, the can itself cools off by significantly more than can be explained by expansion through

    我的意思是,罐子本身的冷卻程度大大超過了通過膨脹所能解釋的程度。

  • a valve , and it's not like it's even being sprayed by the air coming out.

    一個閥門,而且它甚至不像是被噴出的空氣所噴出的。

  • No, the real cooling power is hinted at by the warning labels on cans of compressed air

    不,真正的冷卻能力是由壓縮空氣罐上的警告標籤暗示的。

  • telling you to not to shake them or spray them upside down - if you DO shake one, you'll

    告訴你不要搖晃它們或倒過來噴 - 如果你真的搖晃它們,你會

  • realize right away that it's not just gas inside - there's liquid in there, too!

    馬上意識到裡面不僅僅是氣體--還有液體!"。

  • Liquid like 1,1-difluoroethane, which is a gas at normal temperatures and pressures,

    像1,1-二氟乙烷這樣的液體,在正常溫度和壓力下是一種氣體。

  • but a liquid once you pressurize it to around 6 times atmospheric pressure.

    但一旦你把它加壓到大約6倍大氣壓,就會變成液體。

  • And it's the essential component of these compressed air cans.

    而且它是這些壓縮空氣罐的重要組成部分。

  • Inside the can, 1,1-difluoroethane exists as both a liquid and a gas, in equilibrium

    在罐內,1,1-二氟乙烷既是液體又是氣體,處於平衡狀態。

  • - just enough of the liquid boils off to maintain six atmospheres of pressure in the top of

    - 剛好有足夠的液體沸騰出來,以保持在頂部的六個大氣壓的壓力。

  • the can, a pressure high enough that rest stays liquid.

    罐子裡的壓力足夠高,以便其餘部分保持液體狀態。

  • Because it's at six times atmospheric pressure, when you open the valve the difluoroethane

    因為它的壓力是大氣壓的六倍,當你打開閥門時,二氟乙烷

  • rushes out in a steady stream.

    源源不斷地衝出來。

  • But this then means that the inside of the can is no longer pressurized enough to keep

    但這意味著罐子內部不再有足夠的壓力來保持

  • the liquid from boiling - so more of it boils off until the gas reaches six atmospheres

    液體不會沸騰--是以更多的液體會沸騰,直到氣體達到六個大氣壓。

  • of pressure again and a new equilibrium is reached with slightly less liquid in the can.

    再次加壓,達到新的平衡,罐內液體略少。

  • This is how the can is able to keep blowing a stream of consistent strength even when

    這就是為什麼罐子能夠持續吹出穩定的強度,即使在

  • mostly empty.

    大部分是空的。

  • But more importantly to our temperature conundrum, changes from liquid phase to gas phase require

    但對我們的溫度難題更重要的是,從液相到氣相的變化需要

  • a TON of energy, and that energy has to come from somewhere.

    大量的能量,而這些能量必須來自某處。

  • Just like how the evaporation of sweat removes energy from your skin, cooling you off, inside

    就像汗水的蒸發如何從你的皮膚上帶走能量,使你冷卻下來一樣,在內部

  • a can of compressed air, vaporization - aka boiling - is what steals energy from the liquid

    在一罐壓縮空氣中,汽化--又稱沸騰--是從液體中竊取能量的。

  • and cools it off.

    並將其冷卻。

  • Significantly!

    顯著的!

  • Spraying out 10% of the contents will cool the entire remainder of the can by around

    噴出10%的內容物將使整個罐子的剩餘部分冷卻約10分鐘。

  • 20 degrees celsius!

    攝氏20度!

  • If it seems counterintuitive that a boiling substance cools itself off, look no further

    如果沸騰的物質會自行冷卻,這似乎有悖常理,那就不要再看了

  • than the humble pressure cooker . Water normally boils above 100 degrees celsius, but by sealing

    比起簡陋的快鍋,壓力鍋.水通常會在100攝氏度以上沸騰,但通過密封

  • in steam, the pressure rises, enabling the water in the pot to remain a liquid well beyond

    在蒸汽中,壓力上升,使鍋裡的水保持液體狀態,遠遠超過了水的溫度。

  • water's normal boiling point - just like the difluoroethane in a can of compressed

    水的正常沸點--就像一罐壓縮空氣中的二氟乙烷。

  • air.

    空氣。

  • And releasing water vapor out of the nozzle of a pressure cooker lowers the pressure inside,

    而將水蒸氣從壓力鍋的噴嘴中釋放出來會降低內部的壓力。

  • allowing a bit more water to boil off as steam and lowering the temperature of the remaining

    讓更多的水作為蒸汽沸騰,並降低剩餘的溫度。

  • water - just like the difluoroethane in a compressed air can.

    水 - 就像壓縮空氣罐中的二氟乙烷。

  • And if you keep letting off steam, eventually the water will cool all the way back down

    而如果你繼續放出蒸汽,最終水會一路冷卻下來。

  • to its regular boiling point of 100 degrees , just like how if you keep spraying a can

    到100度的常規沸點,就像你不斷噴灑一罐

  • of compressed air, the difluoroethane inside will cool all the way back down to its regular

    在壓縮空氣的作用下,裡面的二氟乙烷會一直冷卻到其正常狀態。

  • boiling point of negative 25 degrees .

    沸點為負25度。

  • A can of compressed air is quite literally a 1,1-difluoroethane pressure cooker.

    一罐壓縮空氣簡直就是一個1,1-二氟乙烷壓力鍋。

  • And just like you shouldn't shake a pressure cooker or turn it upside down (unless you

    就像你不應該搖晃快鍋,壓力鍋或把它倒過來一樣(除非你

  • want to spray superheated water everywhere), cans of compressed air don't work very well

    想把過熱的水噴得到處都是),壓縮空氣罐的效果不是很好。

  • sideways or upside down: instead of spraying out gas, you'll spray out the liquid that

    側面或顛倒:你不是噴出氣體,而是噴出液體,而不是噴出氣體。

  • was only being kept liquified by the high pressure inside the can , so it immediately

    只有通過罐內的高壓才能保持液化,是以它立即

  • vaporizes and drastically cools down whatever it's contacting . INSTANT ICE! (though difluoroethane

    蒸發並大幅冷卻它所接觸到的東西。瞬間結冰!(儘管二氟乙烷

  • can dissolve in water and is poisonous, so definitely don't use this ice for anything

    可以溶解於水,並且有毒,所以絕對不要用這種冰塊做任何事情。

  • food-related).

    與食品有關)。)

  • In conclusion, the cause for the coldness of cans of compressed air can be clarified

    綜上所述,可以明確壓縮空氣罐的冷度原因

  • by comprehending the consequent clue: they aren't actually cans of compressed air.

    通過理解隨之而來的線索:它們實際上並不是壓縮空氣的罐子。

  • They're cans of pressure-liquified 1,1-difluoroethane, and lowering the pressure inside by spraying

    它們是一罐加壓液化的1,1-二氟乙烷,通過噴灑來降低內部壓力。

  • them allows more liquid to boil off, cooling what remains.

    它們允許更多的液體沸騰,冷卻剩下的液體。

  • I love learning about the physics of regular stuff; I mean, black holes and quantum mechanics

    我喜歡學習常規的物理學知識;我是說,黑洞和量子力學

  • are cool, too, but they're not quite as tangible or relatable as the things we interact

    也很酷,但它們並不像我們互動的東西那樣有形或可親。

  • with on a regular basis.

    偶爾也會與之合作。

  • And if you, too, want to dive deeper into the physics of everyday objects, look no further

    如果你也想更深入地研究日常物品的物理學,就不要再看了

  • than Brilliant, this video's sponsor.

    比起Brilliant,這個視頻的贊助商。

  • Brilliant has a whole course on the physics of everyday objects, including fridges and

    Brilliant有一門關於日常物品的物理學課程,包括冰箱和水壺。

  • water towers and bikes - bikes are great! - and Brilliant also has fun, short daily

    水塔和自行車--自行車是很好的!- 輝煌也有有趣的、簡短的日常

  • challenges and puzzles to learn about stuff like regression to the mean and fluids and

    挑戰和謎題,以瞭解諸如迴歸平均值和流體和的東西。

  • thermodynamics without the huge time commitment it would take to learn enough about Joule-Thompson

    熱力學,而不需要花費大量的時間來學習足夠的焦耳-湯普森知識。

  • expansion through a valve to make a whole youtube video about it

    擴張通過一個閥門,使整個YouTube視頻關於它...

  • Brilliant continues to be an incredible supporter of MinutePhysics and they're offering 20%

    百利公司繼續是MinutePhysics的一個令人難以置信的支持者,他們正在提供20%的優惠。

  • off of a premium subscription to the first 200 of you who go to brilliant.org/minutephysics,

    對前200名進入brilliant.org/minutephysics的人提供高級訂閱的優惠。

  • which gives you full access to all of Brilliant's courses, puzzles and daily challenges.

    這使你可以完全進入Brilliant的所有課程、謎題和每日挑戰。

  • Again, that's brilliant.org/minutephysics for 20% off a premium subscription, and to

    同樣,這也是brilliant.org/minutephysics,可獲得高級訂閱的八折優惠,並可前往

  • let Brilliant know you came from here.

    讓Brilliant知道你來自這裡。

If you've ever used a can of compressed air (also called a gas duster), to, say, clean

如果你曾經使用過一罐壓縮空氣(也稱為氣體吸塵器),例如,清潔

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為什麼壓縮空氣罐會變冷? (Why Do Compressed Air Cans Get Cold?)

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    Summer 發佈於 2021 年 05 月 19 日
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