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  • There are over one billion cars in the world today,

    世界上有超過十億輛汽車

  • getting people where they need to go,

    將人們送到需要到達的地方

  • but cars aren't just a mode of transportation,

    但汽車自並不只是一種交通工具

  • they're also a chemistry lesson waiting to be taught.

    也是一門等著大家去探究的化學課

  • The process of starting your car begins in the engine cylinders,

    啟動汽車的流程始於發動機汽缸

  • where a spritz of gasoline from the fuel injector

    自噴油器先噴出少量汽油

  • and a gulp of air from the intake valve

    加上一點來自進氣閥的空氣

  • mix together before being ignited by a spark,

    兩者均勻混合後再以火花點燃

  • forming gases that expand and push the piston.

    燃燒產生的氣體會膨脹,進而推動活塞

  • But combustion is an exothermic reaction, meaning it releases heat.

    但燃燒是一種釋出能量的放熱反應

  • Lots of it.

    生成很多的能量

  • And while much of this heat escapes through the tail pipe,

    所以縱使很多熱能從排氣管釋出

  • the heat that remains in the engine block needs to be absorbed, transported, and dissipated

    還有許多停留在引擎內的熱能 需要被吸收、傳遞和消散

  • to protect the metal components from deforming or even melting.

    如此才不會使金屬零件變形、甚至熔化

  • This is where the cooling system comes in.

    這就是冷卻系統的作用

  • A liquid gets circulated throughout the engine,

    我們需要液體繞著引擎循環流動吸熱

  • but what kind of liquid can absorb all that heat?

    但是哪種液體能吸收這麼大量的熱能?

  • Water may seem like an obvious first choice.

    水似乎很是首選

  • After all, its specific heat,

    畢竟它的比熱

  • the amount of energy required to raise the temperature

    也就是溫度提升1℃

  • of a given amount by one degree Celsius,

    所需的能量

  • is higher than that of any other common substance.

    比其他相似的物質都還多

  • And we have a lot of heat energy to absorb.

    而我們有很大量的熱能需要被吸收

  • But using water can get us into deep trouble.

    但是如果用水,會帶來很大的麻煩

  • For one thing, its freezing point is zero degrees Celsius.

    例如它的凝固點是0℃

  • Since water expands as it freezes,

    我們知道水結冰時體積會膨脹

  • a cold winter night could mean a cracked radiator and a damaged engine block,

    在寒冷的冬天夜晚,結冰可能 就會導致散熱器破裂或引擎缸體受損

  • a chilling prospect.

    真是令人不寒而慄!

  • And considering how hot car engines can get,

    再者,因為汽車引擎溫度很高

  • the relatively low boiling point of 100 degrees Celsius

    水100℃的沸點就相對太低了

  • can lead to a situation that would get anyone steamed.

    會導致水動輒沸騰

  • So, instead of water, we use a solution,

    所以說,我們需要一種溶液取代水

  • a homogeneous mixture consisting of a solute and a solvent.

    那是一種含有溶質和溶劑的均勻溶液

  • Some of the solution's properties will differ depending on the proportion of solute present.

    有些溶液的性能會隨著 溶質的比例而改變

  • These are called colligative properties, and as luck would have it,

    這叫做「依數性質」,而幸運的是

  • they include freezing point depression and boiling point elevation.

    它可以降低凝固點並提升沸點

  • So, solutions have both a lower freezing point and a higher boiling point than pure solvent,

    所以,溶液有比純溶劑(水) 還低的凝固點及較高的沸點

  • and the more solute is present, the bigger the difference.

    濃度愈高,差別就越大

  • So, why do these properties change?

    為何這些性質會改變呢?

  • First of all, we need to understand that temperature is a measure

    首先,我們需要知道溫度取決於

  • of the particle's average kinetic energy.

    粒子的平均動能

  • The colder the liquid, the less of this energy there is,

    液體溫度越低,所含的能量就越少

  • and the slower the molecules move.

    分子的運動速度也越慢

  • When a liquid freezes, the molecules slow down,

    當液體分子運動速度慢到一定程度時,就會凝固

  • enough for their attractive forces to act on each other,

    慢到讓它們受到彼此引力的牽引

  • arranging themselves into a crystal structure.

    進而形成規則的結晶構造

  • But the presence of solute particles gets in the way of these attractions,

    但溶質分子會阻礙這些作用

  • requiring a solution to be cooled down further before the arrangement can occur.

    所以我們需要一種在 結晶前就能被冷卻的溶液

  • As for the boiling point, when a liquid boils,

    至於沸點,當液體沸騰時

  • it produces bubbles filled with its vapor,

    它會產生充滿蒸氣的氣泡

  • but for a bubble to form, the vapor pressure must become as strong

    但要生成氣泡,液體的蒸氣壓需要

  • as the atmosphere constantly pushing down on the surface of the liquid.

    大到與當時液面的大氣壓力相同

  • As the liquid is heated, the vapor pressure increases,

    當液體升溫時,蒸氣壓會上升

  • and when it becomes equal to the atmospheric pressure,

    當升至與大氣壓力相等時

  • the bubbles form and boiling occurs.

    就會形成氣泡,即是沸騰

  • A solution's vapor pressure is lower than that of pure solvent,

    溶液的蒸氣壓比未加溶質的純溶劑低

  • so it must be heated to an even higher temperature

    所以須被加熱到高於原沸點的溫度

  • before it can match the strength of the atmosphere.

    蒸氣壓才能與大氣壓力一樣大

  • As an added bonus, the pressure in the radiator

    另一項有利的因素是在散熱器中的壓力

  • is kept above atmospheric pressure,

    會保持高於大氣壓力

  • raising the boiling point by another 25 degrees Celsius.

    這可將沸點再提升25℃

  • The solution commonly used for a car's cooling system

    汽車冷卻系統中常用的溶液

  • is a 50/50 mixture of ethylene glycol and water,

    是乙二醇和水1比1比例的混合溶液

  • which freezes at -37 degrees Celsius and boils at 106 degrees Celsius.

    它的凝固點是零下37℃,沸點為106℃

  • At the highest recommended proportion of 70 to 30,

    然而, 最佳比例是7比3

  • the freezing point is even lower at -55 degrees Celsius,

    凝固點甚至低至零下55℃

  • and the boiling point rises to 113 degrees Celsius.

    沸點則高達113℃

  • As you can see, the more ethylene glycol you add,

    由此可知,水中加入越多乙二醇,

  • the more protection you get, so why not go even higher?

    就越能保護汽車,那為何不 多多益善呢?

  • Well, it turns out you can have too much of a good thing

    原因是會「太補」了!

  • because at higher proportions,

    因為在很高濃度時,

  • the freezing point actually starts to go back up.

    凝固點可能反而會上升

  • The properties of the solution head towards the properties of ethylene glycol,

    此特性和乙二醇的性質有關

  • which freezes at -12.9 degrees Celsius,

    乙二醇在零下12.9℃時凝固

  • a higher temperature than we attained with the solution.

    比最佳比例的溶液還高

  • The solution flows through the engine, absorbing heat along the way.

    溶液流經引擎,一路上持續吸收熱能

  • When it reaches the radiator, it's cooled by a fan,

    到達散熱器時,會被風扇

  • as well as air rushing through the front of the car

    及吹入引擎室的空氣冷卻

  • before returning to the hot engine compartment.

    之後再流經引擎

  • So, an effective and safe engine coolant

    所以一種高效率且安全的引擎冷卻液

  • must have a high specific heat, a low freezing point, and a high boiling point.

    必須具有高比熱、 低凝固點及高沸點的特性

  • But instead of searching all over the world for the perfect liquid to solve our problem,

    但除了遍地尋找可以 解決問題的完美液體外

  • we can create our own solution.

    我們還可以自己製造

There are over one billion cars in the world today,

世界上有超過十億輛汽車

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B1 中級 中文 美國腔 TED-Ed 溶液 液體 引擎 大氣 溫度

【TED-Ed】汽車的化學原理 (Under the hood: The chemistry of cars - Cynthia Chubbuck)

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    Chia-Lin Hsin 發佈於 2014 年 09 月 15 日
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