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So when I expand this gas adiabatically and it cools down, why do you think it might cool down?
现在我们知道了气体绝热膨胀时,温度会下载，为什么会降温？
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You take fuel, rather you take something that's warm, and you put it in contact with the atmosphere, it cools down.
改变约束,继续加热,气体膨胀。
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Real refrigerators actually work with liquids that go into gases so use the latent heat of the liquid, so it doesn't really work like the Joule-Thomson expansion. So this is real.
液体变成气体来工作,以运用液体的潜热，所以这不是,真正像焦耳-汤姆逊膨胀一样工作,这是真实的气体，不像焦耳。
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And what we'll discover is that when we allow the gas to expand reversibly, we get the most work. This is neat.
最后将发现,当气体可逆膨胀的时候，对外做功最大。
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So the work that you're doing to expand, to go through this experiment, ends up cooling the gas.
因此在膨胀气体的过程中,气体降温。
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And so an experiment said the gas didn't increase its temperature when it expanded the vacuum.
这个实验告诉你,气体在向真空膨胀的过程,中温度没有升高。
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OK, so we ended up last time, we talked about Joule-Thomson expansion, which is an irreversible expansion through a nozzle, through a porous plug, constant enthalpy expansion.
上节课，我们讨论了焦耳-汤姆逊，膨胀过程,也就是气体，通过毛细管。
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When you expand a real gas into vacuum, the temperature goes down.
当一个真实气体，向真空膨胀咱的时候温度会下降。
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well since the gas is expanding into vacuum no work is done.
因为气体是向真空膨胀,因此这个过程不做功。
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So the Joule free expansion involves opening this valve and asking what happens when this gas moves into the other bulb or distributes between the two.
焦耳自由膨胀就是,打开阀门后的过程,气体从一个腔跑到另一个腔,并在它们之间平均分配。
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What happened to the temperature in a Joule expansion in ideal gas?
对理想气体,焦耳-汤姆逊膨胀过程中温度如何变化？
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The purpose here is to look at a series of processes in which temperature is held constant, and we're going to calculate how much work we get from allowing a gas to expand under various conditions.
目的是让大家了解一下,几个保持温度不变的过程，然后我们将计算,气体在不同膨胀过程中,的对外做功。
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The gas has expanded.
气体膨胀了。
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And here, in an isothermal expansion, The bath is putting back the energy that the gas is expanding or using to expand, and so the energy is flowing back into the gas through the environment in the isothermal expansion.
而在等温膨胀中，恒温环境将气体膨胀对外做功,而损失的能量又返还回来，在等温膨胀中,能量从环境,流向系统。
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