Chapter 18 Second law of thermodynamics Chapter 18: Second Law of Thermodynamics(热力学第二定律) O The second law of thermodynamics ○ Reversible and irreversible process(可逆过程 与不可逆过程 o Carnot cycle(卡诺循环 Entropy(熵)
Chapter 18 Second Law of Thermodynamics The second law of thermodynamics Reversible and irreversible process (可逆过程 与不可逆过程): Carnot cycle(卡诺循环) Chapter 18: Second Law of Thermodynamics（热力学第二定律） Entropy(熵)
Chapter 18 Second law of thermodynamics ◆第二定律的提出 1功热转换的条件第一定律无法说明 2热传导的方向性、气体自由膨胀的不可 逆性问题第一定律无法说明 热力学第二定律的两种表述 1开尔文说法:不可能制造出这样一种循 环工作的热机,它只使单一热源冷却来做功,而 不放出热量给其他物体,或者说不使外界发生任 何变化
Chapter 18 Second Law of Thermodynamics 1 开尔文说法：不可能制造出这样一种循 环工作的热机，它只使单一热源冷却来做功，而 不放出热量给其他物体，或者说不使外界发生任 何变化 . 第二定律的提出 1 功热转换的条件第一定律无法说明. 2 热传导的方向性、气体自由膨胀的不可 逆性问题第一定律无法说明. 一 热力学第二定律的两种表述
Chapter 18 Second law of thermodynamics New words Engine Efficiency 热机效率 Reversible and irreversible process 可逆和不可逆过程p433 Entropy 熵p440
Chapter 18 Second Law of Thermodynamics New words Engine Efficiency 热机效率 Reversible and Irreversible Process 可逆和不可逆过程 p433 Entropy 熵 p440
Chapter 18 Second law of thermodynamics 818-1 The second Law of Thermodynamics P429-430 Some one-way processes P429-430 自然过程是不可逆的,是按一定的方向进行的。 1功热转换p429 通过摩擦而使功变热的过程是不可逆的 例如:飞轮转动、焦耳实验(重物下落)。 The initial potential energy of the rock changes to kinetic energy as the rock falls, but you will never see the reverse happen-a rock at rest on the ground suddenly rise up in the air because the internal energy is transformed into kinetic energy
Chapter 18 Second Law of Thermodynamics §18-1 The second Law of Thermodynamics P429-430 1 功热转换 p429 通过摩擦而使功变热的过程是不可逆的。 例如：飞轮转动、焦耳实验（重物下落）。 The initial potential energy of the rock changes to kinetic energy as the rock falls, but you will never see the reverse happen-a rock at rest on the ground suddenly rise up in the air because the internal energy is transformed into kinetic energy. Some one-way processes P429-430 自然过程是不可逆的，是按一定的方向进行的
Chapter 18 Second law of thermodynamics 2热传导现象P429 热量由高温物体自动地传向低温物体的过 程是不可逆的。 Heat flows naturally from a hot object to a cold object; heat will not flow spontaneously a cold object to a hot object Second Law of Thermodynamics: p430 Heat flows naturally from a hot object to a cold object; heat will not flow spontaneously form a cold object to a hot object
Chapter 18 Second Law of Thermodynamics Heat flows naturally from a hot object to a cold object; heat will not flow spontaneously a cold object to a hot object. 2 热传导现象 P429 热量由高温物体自动地传向低温物体的过 程是不可逆的。 Second Law of Thermodynamics: p430 Heat flows naturally from a hot object to a cold object; heat will not flow spontaneously form a cold object to a hot object
Chapter 18 Second law of thermodynamics §18-3 Reversible and irreversible process(可逆 过程与不可逆过程):p433 Reversible process可逆过程) 无摩擦的准静态过程. Reversible process is carried out infinitely slowly, so that the process can be considered a series of equilibrium states, and the whole process could be done in reverse with no change in magnitude of the work done or heat exchanged
Chapter 18 Second Law of Thermodynamics §18-3 Reversible and irreversible process (可逆 过程与不可逆过程): p433 Reversible process(可逆过程) ----无摩擦的准静态过程. Reversible process is carried out infinitely slowly, so that the process can be considered a series of equilibrium states, and the whole process could be done in reverse with no change in magnitude of the work done or heat exchanged
Chapter 18 Second law of thermodynamics ◆可逆过程:在系统状态变化过程中,如果 逆过程能重复正过程的每一状态,而不引起其 他变化,这样的过程叫做可逆过程 准静态等温过程P4 执 源 (P2,V2,7) T 准静态无摩擦过程为可逆过程
Chapter 18 Second Law of Thermodynamics 准静态无摩擦过程为可逆过程 可逆过程 : 在系统状态变化过程中,如果 逆过程能重复正过程的每一状态, 而不引起其 他变化, 这样的过程叫做可逆过程
Chapter 18 Second law of thermodynamics Irreversible process is one that can not be reversed by means of small changes in the environment 在不引起其他变化的条件下,不能使逆过程重 复正过程的每一个状态的过程称为不可逆过程 (自然过程都是不可逆的) All real process are irreversible 非准静态过程为∵ 不可逆过程
Chapter 18 Second Law of Thermodynamics Irreversible process is one that can not be reversed by means of small changes in the environment. 在不引起其他变化的条件下,不能使逆过程重 复正过程的每一个状态的过程称为不可逆过程. (自然过程都是不可逆的) All real process are irreversible. 非准静态过程为 不可逆过程
Chapter 18 Second law of thermodynamics 818-2 Heat Engines P430 The working substances absorb heat from high temperature resource, High ternperature one part of energy becomes work. and Steam Water the other part release Intake valve Boiler (open dluring to the low expansIon) temperature resource After a cycle, the Exhaust valve Piston (closed during ekpilnsltlll working substances Pum resume their original ( wate Condenser state。 Low tcmpcraturc
Chapter 18 Second Law of Thermodynamics §18-2 Heat Engines P430 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. After a cycle, the working substances resume their original state
Chapter 18 Second law of thermodynamics 1热机发展简介 历史上热力学理论最初是在研究热机工作过程的基 础上发展起来的。热机是利用热来做功的机器。1698 年萨维利和1705年纽可门先后发明了蒸汽机,当时蒸 汽机的效率极低.1765年瓦特进行了重大改进,大大 提高了效率.人们一直在为提高热机的效率而努力,从 理论上研究热机效率问题,一方面指明了提高效率的 方向,另一方面也推动了热学理论的发展 各种热机的效率 液体燃料火箭=48%柴油机7=37 汽油机 7=25%蒸汽机m=8%
Chapter 18 Second Law of Thermodynamics 历史上热力学理论最初是在研究热机工作过程的基 础上发展起来的。热机是利用热来做功的机器。1698 年萨维利和1705年纽可门先后发明了蒸汽机，当时蒸 汽机的效率极低 . 1765年瓦特进行了重大改进 ，大大 提高了效率 .人们一直在为提高热机的效率而努力，从 理论上研究热机效率问题， 一方面指明了提高效率的 方向， 另一方面也推动了热学理论的发展 . 各种热机的效率 液体燃料火箭 柴油机 汽油机 蒸汽机 = 48% = 8% = 37% = 25% 1 热机发展简介