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此词条暂由彩云小译翻译，未经人工整理和审校，带来阅读不便，请见谅。{{short description|Law of physics}}

此词条暂由彩云小译翻译，未经人工整理和审校，带来阅读不便，请见谅。{{short description|Law of physics}}

 

{{Thermodynamics|laws}}

{{Thermodynamics|laws}}

[[File:Heat flow hot to cold.png|thumb|upright|Heat flow from hot water to cold water. 热量总是从热水流向冷水]]

[[File:Heat flow hot to cold.png|thumb|upright|Heat flow from hot water to cold water. 热总是从热水流向冷水]]

The first law of thermodynamics provides the definition of the internal energy of a thermodynamic system, and expresses the law of conservation of energy. The second law is concerned with the direction of natural processes. It asserts that a natural process runs only in one sense, and is not reversible. For example, when a path for conduction and radiation is made available, heat always flows spontaneously from a hotter to a colder body. Such phenomena are accounted for in terms of entropy. If an isolated system is held initially in internal thermodynamic equilibrium by internal partitioning impermeable walls, and then some operation makes the walls more permeable, then the system spontaneously evolves to reach a final new internal thermodynamic equilibrium, and its total entropy, S, increases.

The first law of thermodynamics provides the definition of the internal energy of a thermodynamic system, and expresses the law of conservation of energy. The second law is concerned with the direction of natural processes. It asserts that a natural process runs only in one sense, and is not reversible. For example, when a path for conduction and radiation is made available, heat always flows spontaneously from a hotter to a colder body. Such phenomena are accounted for in terms of entropy. If an isolated system is held initially in internal thermodynamic equilibrium by internal partitioning impermeable walls, and then some operation makes the walls more permeable, then the system spontaneously evolves to reach a final new internal thermodynamic equilibrium, and its total entropy, S, increases.

'''热力学第一定律 First Law Of Thermodynamics''' <font color = 'red'><s>对</s></font> <font color = 'blue'>定义了</font>热力学系统所涉及到的'''内能 Internal Energy'''<font color = 'red'><s>进行了定义</s></font> ，并体现了能量守恒定律。热力学第二定律与'''自然过程Natural Processes'''的方向有关。它<font color = 'red'><s>设定</s></font> <font color = 'blue'>断言</font>自然过程只在一种意义上进行，且<font color = 'red'><s>是</s></font> 不可逆<font color = 'red'><s>的</s></font> 。例如，当有了传导和辐射的（传播）路径时，热量总是自发地从一个较热的物体流向一个较冷的物体。这种现象可以用'''熵Entropy'''来解释。<font color = 'red'>若一个孤立系统最初在内部不可渗透的薄膜维持内部的热力学平衡，通过一些操作使得薄膜具有渗透性，则该系统可自发地演变，最终达到一个新的内部热力学平衡，其总熵增加。</font>

'''热力学第一定律 First Law Of Thermodynamics''' <font color = 'red'><s>对</s></font> <font color = 'blue'>定义了</font>热力学系统所涉及到的'''内能 Internal Energy'''<font color = 'red'><s>进行了定义</s></font> ，并体现了能量守恒定律。热力学第二定律与'''自然过程Natural Processes'''的方向有关。它<font color = 'red'><s>设定</s></font> <font color = 'blue'>断言</font>自然过程只在一种意义上进行，且<font color = 'red'><s>是</s></font> 不可逆<font color = 'red'><s>的</s></font> 。例如，当有了传导和辐射的（传播）路径时，热<s>量</s>总是自发地从一个较热的物体流向一个较冷的物体。这种现象可以用'''熵Entropy'''来解释。<font color = 'red'>若一个孤立系统最初在内部不可渗透的薄膜维持内部的热力学平衡，通过一些操作使得薄膜具有渗透性，则该系统可自发地演变，最终达到一个新的内部热力学平衡，其总熵增加。</font>

<font color = 'blue'>若一个'''孤立系统Isolated System'''最初在具有隔热内壁的系统内维持热力学平衡，通过一些操作使内壁透热，则该系统可自发地演变，最终达到一个新的内部热力学平衡，且其总熵{{math|''S''}}增加。</font>

<font color = 'blue'>若一个'''孤立系统Isolated System'''最初在具有隔热内壁的系统内维持热力学平衡，通过一些操作使内壁透热，则该系统可自发地演变，最终达到一个新的内部热力学平衡，且其总熵{{math|''S''}}增加。</font>

In a fictive reversible process, an infinitesimal increment in the entropy () of a system is defined to result from an infinitesimal transfer of heat () to a closed system (which allows the entry or exit of energy – but not transfer of matter) divided by the common temperature () of the system in equilibrium and the surroundings which supply the heat:

In a fictive reversible process, an infinitesimal increment in the entropy () of a system is defined to result from an infinitesimal transfer of heat () to a closed system (which allows the entry or exit of energy – but not transfer of matter) divided by the common temperature () of the system in equilibrium and the surroundings which supply the heat:

在<font color = 'red'><s>设置的虚拟</s></font> <font color = 'blue'>假想的</font>可逆过程中，系统的熵的无穷小增量<math>dS</math>被定义为由无穷小的热量<math>δQ</math>传递到一个封闭系统(允许能量进入或出去，但不允许物质传递<blue>的系统</blue>)除以<blue>该</blue>平衡系统和提供热量的环境的共同温度 <math>T</math>:

在<font color = 'red'><s>设置的虚拟</s></font> <font color = 'blue'>假想的</font>可逆过程中，系统的熵的无穷小增量<math>dS</math>被定义为由无穷小的热<s>量</s><math>δQ</math>传递到一个封闭系统(允许能量进入或出去，但不允许物质传递<blue>的系统</blue>)除以<blue>该</blue>平衡系统和提供热<s>量</s>的环境的共同温度 <math>T</math>:

Different notations are used for infinitesimal amounts of heat () and infinitesimal amounts of entropy () because entropy is a function of state, while heat, like work, is not. For an actually possible infinitesimal process without exchange of mass with the surroundings, the second law requires that the increment in system entropy fulfills the inequality   

Different notations are used for infinitesimal amounts of heat () and infinitesimal amounts of entropy () because entropy is a function of state, while heat, like work, is not. For an actually possible infinitesimal process without exchange of mass with the surroundings, the second law requires that the increment in system entropy fulfills the inequality   

用不同的符号''δ''和''d''表示无穷小量的热量和无穷小量的熵，因为熵是状态函数，而热量和功一样<font color = 'blue'>则</font>不是状态函数。<font color = 'red'><s>第二定律要求系统熵的增量满足不等式，</s></font>对于实际上可能存在的不与环境发生<font color = 'red'><s>质量</s></font><font color = 'blue'>物质</font>交换的无穷小过程，<font color = 'blue'>第二定律要求</font>系统熵增量满足不等式：

用不同的符号''δ''和''d''表示无穷小量的热<s>量</s>和无穷小量的熵，因为熵是状态函数，而热<s>量</s>和功一样<font color = 'blue'>则</font>不是状态函数。<font color = 'red'><s>第二定律要求系统熵的增量满足不等式，</s></font>对于实际上可能存在的不与环境发生<font color = 'red'><s>质量</s></font><font color = 'blue'>物质</font>交换的无穷小过程，<font color = 'blue'>第二定律要求</font>系统熵增量满足不等式：

   --[[用户:嘉树|嘉树]]（[[用户讨论:嘉树|讨论]]） 根据上下文（讲到封闭系统），此处疑“mass”译为物质更佳

   --[[用户:嘉树|嘉树]]（[[用户讨论:嘉树|讨论]]） 根据上下文（讲到封闭系统），此处疑“mass”译为物质更佳

热力学第二定律的历史起源是'''卡诺原理Carnot's principle'''。

热力学第二定律的历史起源是'''卡诺原理Carnot's principle'''。

它指的是'''卡诺热机Carnot heat engine'''的一个循环，<font color = 'red'><s>它</s></font><font color = 'blue'>卡诺热机</font>以'''准静态quasi-static'''的极限慢速运转，因此热量和功在子系统之间进行传递，子系统总是处于它们自己内部的热力学平衡状态。

它指的是'''卡诺热机Carnot heat engine'''的一个循环，<font color = 'red'><s>它</s></font><font color = 'blue'>卡诺热机</font>以'''准静态quasi-static'''的极限慢速运转，因此热<s>量</s>和功在子系统之间进行传递，子系统总是处于它们自己内部的热力学平衡状态。

卡诺热机是研究热机效率的工程师特别感兴趣的理想装置。

卡诺热机是研究热机效率的工程师特别感兴趣的理想装置。

当卡诺发现卡诺原理时，'''热量理论caloric theory of heat'''还没有得到重视，热力学第一定律还没有得到承认，熵的概念还没有数学表达。

当卡诺发现卡诺原理时，'''热量理论caloric theory of heat'''还没有得到重视，热力学第一定律还没有得到承认，熵的概念还没有数学表达。

The motive power of heat is independent of the agents employed to realize it; its quantity is fixed solely by the temperatures of the bodies between which is effected, finally, the transfer of caloric.

The motive power of heat is independent of the agents employed to realize it; its quantity is fixed solely by the temperatures of the bodies between which is effected, finally, the transfer of caloric.

热量的原动力与实现热的媒介无关，<font color = 'red'><s>热量的数量</s></font><font color = 'blue'>热的量</font>完全取决于两个物体之间的温度，最后是热量的传递。

热<s>量</s>的原动力与实现热的媒介无关，<font color = 'red'><s>热量的数量</s></font><font color = 'blue'>热的量</font>完全取决于两个物体之间的温度，最后是热量的传递。

<blockquote>Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time.</blockquote>

<blockquote>Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time.</blockquote>

The statement by Clausius uses the concept of 'passage of heat'. As is usual in thermodynamic discussions, this means 'net transfer of energy as heat', and does not refer to contributory transfers one way and the other.

The statement by Clausius uses the concept of 'passage of heat'. As is usual in thermodynamic discussions, this means 'net transfer of energy as heat', and does not refer to contributory transfers one way and the other.

克劳修斯的表述使用了“'''热量通道Passage Of Heat'''”的概念。<font color = 'red'><s>正如通常在热力学的讨论，这意味着“能量作为热量的净转移” ，而不是另一种形式上的"分摊转账"或其他。</s></font><font color = 'blue'>

克劳修斯的表述使用了“'''热通道Passage Of Heat'''”的概念。<font color = 'red'><s>正如通常在热力学的讨论，这意味着“能量作为热的净转移” ，而不是另一种形式上的"分摊转账"或其他。</s></font><font color = 'blue'>

在热力学的讨论中，通常这意味着“能量作为热的形式的净转移” ，而不是指其他方式的转移。</font>

在热力学的讨论中，通常这意味着“能量作为热的形式的净转移” ，而不是指其他方式的转移。</font>

   --[[用户:趣木木|趣木木]]（[[用户讨论:趣木木|讨论]]）不太理解分摊转账contributory transfers  

   --[[用户:趣木木|趣木木]]（[[用户讨论:趣木木|讨论]]）不太理解分摊转账contributory transfers  

Heat cannot spontaneously flow from cold regions to hot regions without external work being performed on the system, which is evident from ordinary experience of refrigeration, for example. In a refrigerator, heat flows from cold to hot, but only when forced by an external agent, the refrigeration system.

Heat cannot spontaneously flow from cold regions to hot regions without external work being performed on the system, which is evident from ordinary experience of refrigeration, for example. In a refrigerator, heat flows from cold to hot, but only when forced by an external agent, the refrigeration system.

如果不对系统<font color = 'red'><s>进行外部功</s></font><font color = 'blue'>外部做功</font>，热量<font color = 'red'><s>就</s></font>不能自发地从冷区流向热区，这一点从制冷的普通经验中也可以看出。在冰箱中，<font color = 'red'><s>热量从冷到热，但只有在外部媒介——制冷系统的强制作用下才会发生变化。</s></font><font color = 'blue'>只有在外部媒介也就是制冷系统的强制作用下热才会从冷区流到热区。</font>

如果不对系统<font color = 'red'><s>进行外部功</s></font><font color = 'blue'>外部做功</font>，热<font color = 'red'><s>量就</s></font>不能自发地从冷区流向热区，这一点从制冷的普通经验中也可以看出。在冰箱中，<font color = 'red'><s>热量从冷到热，但只有在外部媒介——制冷系统的强制作用下才会发生变化。</s></font><font color = 'blue'>只有在外部媒介也就是制冷系统的强制作用下热才会从冷区流到热区。</font>

Suppose there is an engine violating the Kelvin statement: i.e., one that drains heat and converts it completely into work in a cyclic fashion without any other result. Now pair it with a reversed Carnot engine as shown by the figure. The efficiency of a normal heat engine is η and so the efficiency of the reversed heat engine is 1/η. The net and sole effect of the combined pair of engines is to transfer heat from <math>\Delta Q=Q\left(\frac{1}{\eta}-1\right)</math> the cooler reservoir to the hotter one, which violates the Clausius statement. (This is a consequence of the first law of thermodynamics, as for the total system's energy to remain the same, <math> \text{Input}+\text{Output}=0 \implies Q-\frac{Q}{\eta} = -Q_c </math>, so therefore <math> Q_c=Q\left( \frac{1}{\eta}-1\right) </math> ). Thus a violation of the Kelvin statement implies a violation of the Clausius statement, i.e. the Clausius statement implies the Kelvin statement. We can prove in a similar manner that the Kelvin statement implies the Clausius statement, and hence the two are equivalent.

Suppose there is an engine violating the Kelvin statement: i.e., one that drains heat and converts it completely into work in a cyclic fashion without any other result. Now pair it with a reversed Carnot engine as shown by the figure. The efficiency of a normal heat engine is η and so the efficiency of the reversed heat engine is 1/η. The net and sole effect of the combined pair of engines is to transfer heat from <math>\Delta Q=Q\left(\frac{1}{\eta}-1\right)</math> the cooler reservoir to the hotter one, which violates the Clausius statement. (This is a consequence of the first law of thermodynamics, as for the total system's energy to remain the same, <math> \text{Input}+\text{Output}=0 \implies Q-\frac{Q}{\eta} = -Q_c </math>, so therefore <math> Q_c=Q\left( \frac{1}{\eta}-1\right) </math> ). Thus a violation of the Kelvin statement implies a violation of the Clausius statement, i.e. the Clausius statement implies the Kelvin statement. We can prove in a similar manner that the Kelvin statement implies the Clausius statement, and hence the two are equivalent.

假设有一个热机违反了开尔文定理: 也就是说，这个热机以循环的方式吸收热量并将其<font color = 'blue'>完全</font>转化为功，而<font color = 'blue'>且</font>不产生任何影响。现<font color = 'blue'>在将其</font>与反向卡诺<font color = 'red'><s>发动</s></font>机<font color = 'red'><s>相对应</s></font><font color = 'blue'>比较</font>，如图所示。

假设有一个热机违反了开尔文定理: 也就是说，这个热机以循环的方式吸收热<s>量</s>并将其<font color = 'blue'>完全</font>转化为功，而<font color = 'blue'>且</font>不产生任何影响。现<font color = 'blue'>在将其</font>与反向卡诺<font color = 'red'><s>发动</s></font>机<font color = 'red'><s>相对应</s></font><font color = 'blue'>比较</font>，如图所示。

普通热机的效率为η，反向热机的效率为1/η。这对<font color = 'red'><s>热机的联合作用为</s></font><font color = 'blue'>联合热机的净效应和唯一效应是</font><math>\Delta Q=Q\left(\frac{1}{\eta}-1\right)</math> 将热量从较冷热源<font color = 'blue'>转移</font>到较热热源，这违反了克劳修斯表述。（这是能量守恒定律的结果，因为系统的总能量保持不变<math> \text{Input}+\text{Output}=0 \implies Q-\frac{Q}{\eta} = -Q_c </math>，所以<math> Q_c=Q\left( \frac{1}{\eta}-1\right) </math>。）因此，违反开尔文表述意味着违反克劳修斯表述，即克劳修斯表述暗示了开尔文表述。我们可以用类似的方式证明开尔文表述暗示了克劳修斯表述，因此两者是等价的。

普通热机的效率为η，反向热机的效率为1/η。这对<font color = 'red'><s>热机的联合作用为</s></font><font color = 'blue'>联合热机的净效应和唯一效应是</font><math>\Delta Q=Q\left(\frac{1}{\eta}-1\right)</math> 将热<s>量</s>从较冷热源<font color = 'blue'>转移</font>到较热热源，这违反了克劳修斯表述。（这是能量守恒定律的结果，因为系统的总能量保持不变<math> \text{Input}+\text{Output}=0 \implies Q-\frac{Q}{\eta} = -Q_c </math>，所以<math> Q_c=Q\left( \frac{1}{\eta}-1\right) </math>。）因此，违反开尔文表述意味着违反克劳修斯表述，即克劳修斯表述暗示了开尔文表述。我们可以用类似的方式证明开尔文表述暗示了克劳修斯表述，因此两者是等价的。

It is impossible to devise a cyclically operating device, the sole effect of which is to absorb energy in the form of heat from a single thermal reservoir and to deliver an equivalent amount of work.

It is impossible to devise a cyclically operating device, the sole effect of which is to absorb energy in the form of heat from a single thermal reservoir and to deliver an equivalent amount of work.

===Planck's statement 普朗克表述===

===Planck's statement 普朗克表述===

With this formulation, he described the concept of adiabatic accessibility for the first time and provided the foundation for a new subfield of classical thermodynamics, often called geometrical thermodynamics. It follows from Carathéodory's principle that quantity of energy quasi-statically transferred as heat is a holonomic process function, in other words, <math>\delta Q=TdS</math>.  

With this formulation, he described the concept of adiabatic accessibility for the first time and provided the foundation for a new subfield of classical thermodynamics, often called geometrical thermodynamics. It follows from Carathéodory's principle that quantity of energy quasi-statically transferred as heat is a holonomic process function, in other words, <math>\delta Q=TdS</math>.  

<font color = 'red'><s>公理化处理后，</s></font><font color = 'blue'>通过这个阐明，</font>他<font color = 'red'><s>第一次</s></font><font color = 'blue'>首次</font>描述了'''绝热可达性 Adiabatic Accessibility'''的概念，并成为经典热力学的一个新的子领域，即通常所说的'''几何热力学  Geometrical Thermodynamics'''<font color = 'red'><s>奠定了基础</s></font>。由卡拉西奥多里原理可以推出，<font color = 'red'><s>准静态转移的热量值是一个可积过程函数，</s></font><font color = 'blue'>作为热的能量的准静态转移是一个完整的过程函数</font>即<math>\delta Q=TdS</math>。

<font color = 'red'><s>公理化处理后，</s></font><font color = 'blue'>通过这个阐明，</font>他<font color = 'red'><s>第一次</s></font><font color = 'blue'>首次</font>描述了'''绝热可达性 Adiabatic Accessibility'''的概念，并成为经典热力学的一个新的子领域，即通常所说的'''几何热力学  Geometrical Thermodynamics'''<font color = 'red'><s>奠定了基础</s></font>。由卡拉西奥多里原理可以推出，<font color = 'red'><s>准静态转移的热的值是一个可积过程函数，</s></font><font color = 'blue'>作为热的能量的准静态转移是一个完整的过程函数</font>即<math>\delta Q=TdS</math>。

  --[[用户:Dorr|Dorr]]（[[用户讨论:Dorr|讨论]]）准静态转移的热量值是一个可积过程函数 存疑

  --[[用户:Dorr|Dorr]]（[[用户讨论:Dorr|讨论]]）准静态转移的热量值是一个可积过程函数 存疑

... there is only one way in which the entropy of a [closed] system can be decreased, and that is to transfer heat from the system.

... there is only one way in which the entropy of a [closed] system can be decreased, and that is to transfer heat from the system.

……只有一种方法可以减少<font color = 'red'><s>[闭合]</s></font><font color = 'blue'>（封闭）</font>系统的熵，那就是从系统中转移热量。

……只有一种方法可以减少<font color = 'red'><s>[闭合]</s></font><font color = 'blue'>（封闭）</font>系统的熵，<font color = 'red'><s>那就是从系统中转移热量</s></font><font color = 'blue'>将热从系统中转移出去</font>。

In his ideal model, the heat of caloric converted into work could be reinstated by reversing the motion of the cycle, a concept subsequently known as thermodynamic reversibility. Carnot, however, further postulated that some caloric is lost, not being converted to mechanical work. Hence, no real heat engine could realise the Carnot cycle's reversibility and was condemned to be less efficient.

In his ideal model, the heat of caloric converted into work could be reinstated by reversing the motion of the cycle, a concept subsequently known as thermodynamic reversibility. Carnot, however, further postulated that some caloric is lost, not being converted to mechanical work. Hence, no real heat engine could realise the Carnot cycle's reversibility and was condemned to be less efficient.

在他的理想模型中，<font color = 'red'><s>热转换成功</s></font><font color = 'blue'>热转化为功的过程</font>可以通过逆转循环的运动而恢复，这个概念后来被称为'''热力学可逆性 Thermodynamic Reversibility'''。然而，卡诺进一步假定，一些热量损失了，并没有转化为机械功。因此，没有一个真实的热机能够实现'''卡诺循环 Carnot Cycle'''的可逆性，并且被认为效率较低。

在他的理想模型中，<font color = 'red'><s>热转换成功</s></font><font color = 'blue'>热转化为功的过程</font>可以通过逆转循环的运动而恢复，这个概念后来被称为'''热力学可逆性 Thermodynamic Reversibility'''。然而，卡诺进一步假定，一些热<s>量</s>损失了，并没有转化为机械功。因此，没有一个真实的热机能够实现'''卡诺循环 Carnot Cycle'''的可逆性，并且被认为效率较低。

Though formulated in terms of caloric (see the obsolete caloric theory), rather than entropy, this was an early insight into the second law.

Though formulated in terms of caloric (see the obsolete caloric theory), rather than entropy, this was an early insight into the second law.

该理论尽管是用热量表述的（见被取代的'''<font color = 'red'><s>热质说</s></font><font color = 'blue'>热量理论</font> Caloric Theory'''），而不是熵，但是它是对第二定律的早期认识。

该理论尽管是用热<s>量</s>表述的（见被取代的'''<font color = 'red'><s>热质说</s></font><font color = 'blue'>热量理论</font> Caloric Theory'''），而不是熵，但是它是对第二定律的早期认识。

   --[[用户:嘉树|嘉树]]（[[用户讨论:嘉树|讨论]]） “热质说”的翻译存疑

   --[[用户:嘉树|嘉树]]（[[用户讨论:嘉树|讨论]]） “热质说”的翻译存疑

<font color = 'red'><s>19世纪提出的开尔文-普朗克第二定律(Kelvin-Planck)表示：“任何循环运行的设备都不可能从单个蓄热体接收热量并产生净功。”这被证明相当于克劳修斯的陈述。</s></font><font color = 'blue'>19世纪提出的开尔文-普朗克第二陈述(Kelvin-Planck)表示：“任何循环运行的设备都不可能从单个热源接收热并产生净功。”这被证明与克劳修斯的陈述等价。</font>

<font color = 'red'><s>19世纪提出的开尔文-普朗克第二定律(Kelvin-Planck)表示：“任何循环运行的设备都不可能从单个蓄热体接收热<s>量</s>并产生净功。”这被证明相当于克劳修斯的陈述。</s></font><font color = 'blue'>19世纪提出的开尔文-普朗克第二陈述(Kelvin-Planck)表示：“任何循环运行的设备都不可能从单个热源接收热并产生净功。”这被证明与克劳修斯的陈述等价。</font>

The expression of the second law for closed systems (so, allowing heat exchange and moving boundaries, but not exchange of matter) is:

The expression of the second law for closed systems (so, allowing heat exchange and moving boundaries, but not exchange of matter) is:

封闭系统的第二定律(允许热量交换和移动边界，但不允许物质交换)的表达式是:

封闭系统的第二定律(允许热<s>量</s>交换和移动边界，但不允许物质交换)的表达式是:

To a fair approximation, living organisms may be considered as examples of (b). Approximately, an animal's physical state cycles by the day, leaving the animal nearly unchanged. Animals take in food, water, and oxygen, and, as a result of metabolism, give out breakdown products and heat. Plants take in radiative energy from the sun, which may be regarded as heat, and carbon dioxide and water. They give out oxygen. In this way they grow. Eventually they die, and their remains rot away, turning mostly back into carbon dioxide and water. This can be regarded as a cyclic process. Overall, the sunlight is from a high temperature source, the sun, and its energy is passed to a lower temperature sink, i.e. radiated into space. This is an increase of entropy of the surroundings of the plant. Thus animals and plants obey the second law of thermodynamics, considered in terms of cyclic processes. Simple concepts of efficiency of heat engines are hardly applicable to this problem because they assume closed systems.

To a fair approximation, living organisms may be considered as examples of (b). Approximately, an animal's physical state cycles by the day, leaving the animal nearly unchanged. Animals take in food, water, and oxygen, and, as a result of metabolism, give out breakdown products and heat. Plants take in radiative energy from the sun, which may be regarded as heat, and carbon dioxide and water. They give out oxygen. In this way they grow. Eventually they die, and their remains rot away, turning mostly back into carbon dioxide and water. This can be regarded as a cyclic process. Overall, the sunlight is from a high temperature source, the sun, and its energy is passed to a lower temperature sink, i.e. radiated into space. This is an increase of entropy of the surroundings of the plant. Thus animals and plants obey the second law of thermodynamics, considered in terms of cyclic processes. Simple concepts of efficiency of heat engines are hardly applicable to this problem because they assume closed systems.

从近似的角度来看，生命体可以被认为是(b)的一个例子。近似地，一只动物的身体状态每天循环，使得它几乎没有什么变化。动物吸收食物、水和氧气，经过'''新陈代谢metabolism'''，输出分解的产物和热量。植物吸收来自太阳的辐射能量，这可以认为是热量，以及二氧化碳和水，然后它们释放氧气。它们就是这样生长的，最终会死亡，尸体腐烂，大部分重新变成二氧化碳和水。这可以看作是一个循环过程。总的来说，阳光来自一个高温的源——太阳，它的能量被传递到一个较低的温度汇，例如向太空辐射。这个过程使得植物周围环境的熵增加。因此从循环过程的角度来看，动物和植物服从热力学第二定律。简单的热机效率概念很难适用于这个问题，因为它们假定系统是封闭的。

从近似的角度来看，生命体可以被认为是(b)的一个例子。近似地，一只动物的身体状态每天循环，使得它几乎没有什么变化。动物吸收食物、水和氧气，经过'''新陈代谢metabolism'''，输出分解的产物和热<s>量</s>。植物吸收来自太阳的辐射能量，这可以认为是热<s>量</s>，以及二氧化碳和水，然后它们释放氧气。它们就是这样生长的，最终会死亡，尸体腐烂，大部分重新变成二氧化碳和水。这可以看作是一个循环过程。总的来说，阳光来自一个高温的源——太阳，它的能量被传递到一个较低的温度汇，例如向太空辐射。这个过程使得植物周围环境的熵增加。因此从循环过程的角度来看，动物和植物服从热力学第二定律。简单的热机效率概念很难适用于这个问题，因为它们假定系统是封闭的。