Chapter 18 Second law of thermodynamics 热机:持续地将热量转变为功的机器 冷凝器 play stop 工作物质(工质):热机中被利用来吸收热量 并对外做功的物质
Chapter 18 Second Law of Thermodynamics 热机 ：持续地将热量转变为功的机器 . 工作物质（工质）：热机中被利用来吸收热量 并对外做功的物质
Chapter 18 Second law of thermodynamics 2 Schematic working process of steam engine 热机从高温热源吸 取热量,一部分转变成 功,另一部分放到低温 高温热源T1 热源。T he working substances absorb heat Q 热机 from high temperature resource; one part of W energy becomes work, 放 and the other part release to the ow 低温热源T2 temperature resource
Chapter 18 Second Law of Thermodynamics 高温热源T1 低温热源T2 热机 W Q放 Q吸 热机从高温热源吸 取热量，一部分转变成 功，另一部分放到低温 热 源 。 The working substances absorb heat from high temperature resource; one part of energy becomes work, and the other part release to the low temperature resource. 2 Schematic working process of steam engine
Chapter 18 Second law of thermodynamics 3循环过程 Cycle 系统经过一系列变化状态过程后,又回到 原来的状态的过程叫热力学循环过程 In general, if a system starts from a certain initial pt a state, through a closed series of thermodynamic processes, the system B returns to its initial state, then these processes are called a cycle
Chapter 18 Second Law of Thermodynamics In general, if a system starts from a certain initial state, through a closed series of thermodynamic processes, the system returns to its initial state, then these processes are called a cycle. 3 循环过程Cycle 系统经过一系列变化状态过程后，又回到 原来的状态的过程叫热力学循环过程 . p o V A B VA VB c d
Chapter 18 Second law of thermodynamics 4循环过程的特点 important features of cyclic process 经过一个循环,内能不变。△U=0 循环曲线为闭合曲线。 ·循环曲线所包围的面 B 积为系统做的净功
Chapter 18 Second Law of Thermodynamics 4 循环过程的特点 important features of cyclic process •经过一个循环，内能不变。 •循环曲线所包围的面 积为系统做的净功。 •循环曲线为闭合曲线。 DU = 0 p o V W A B VA VB c d
Chapter 18 Second law of thermodynamics 从状态A经状态c达到状态B,系统对外界做功W1, W=S VAcBY 从状态A经状态达到状态 B,外界对系统做功W2, B W=S 2 VAAdBVB O B 系统对外做净功的数值为W=WrW2 adBc
Chapter 18 Second Law of Thermodynamics p o V W A B VA VB c d 从状态A经状态c达到状态B，系统对外界做功W1， 系统对外做净功的数值为W=W1 -W2 VA AcBVB W1 = S 从状态A经状态d达到状态 B，外界对系统做功W2， VA AdBVB W2 = S W = SAdBc