Second Law of Thermodynamics

The Thermal Bottleneck

热瓶颈

If the first law of thermodynamics says you can't win, then the Second Law of Thermodynamics says you can't even break even. The First Law is essentially a statement of conservation of energy and asserts that you can't get more energy out of a heat engine than you put in. But the Second Law says that no heat engine can use all the heat produced by a fuel to do work. The Carnot cycle sets the ideal efficiency which can be obtained if there is no friction, mechanical losses, leakage, etc., but real machine efficiencies are much less.

如果第一热力学定律说你无法赢，那么第二热力学定律说你甚至无法保本。第一定律本质上是能量守恒的陈述，并断言你不能从热机中得到比投入更多的能量。但第二定律指出，没有任何热机能利用燃料产生的全部热量来做功。卡诺循环设定了在没有摩擦、机械损失、泄漏等情况下的理想效率，但实际机器的效率要低得多。

Qualitative Statements: Second Law of Thermodynamics

定性陈述：热力学第二定律

The second law of thermodynamics is a profound principle of nature which affects the way energy can be used. There are several approaches to stating this principle qualitatively. Here are some approaches to giving the basic sense of the principle.

热力学第二定律是自然界的一个深刻原理，它影响着能量的使用方式。有几种方法可以定性地表述这一原理。以下是一些表述该原理基本含义的方法。

1. Heat will not flow spontaneously from a cold object to a hot object.

热量不会自发地从冷物体传到热物体。

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2. Any system which is free of external influences becomes more disordered with time. This disorder can be expressed in terms of the quantity called entropy.

任何不受到外部影响的系统，随着时间的推移会变得更加无序。这种无序程度可以用一个称为熵的量来表示。

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3. You cannot create a heat engine which extracts heat and converts it all to useful work.

你不能制造一个热机，它从热源中提取热量并将其全部转化为有用功。

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4. There is a thermal bottleneck which constrains devices which convert stored energy to heat and then use the heat to accomplish work. For a given mechanical efficiency of the devices, a machine which includes the conversion to heat as one of the steps will be inherently less efficient than one which is purely mechanical.

存在一个热瓶颈，它限制了将存储的能转化为热能，然后利用热能完成功的装置。对于给定的机械效率，将热能转换作为一步的机器会比纯粹机械的机器效率更低。

Further
discussion

进一步讨论