1、第一章 基本概念 Chapter 1. Basic Concepts,Contents,1.1 Thermodynamic System 热力系统1.2 Properties of A System系统的状态参数1.3 State and Equilibrium状态及平衡状态1.4 Process and Cycles过程与循环,,Company Logo,Terminology(术语）,closed system 闭口系统 open system 开口系统 adiabatic system 绝热系统 isolated system 孤立系统 boundary 边界 surrounding 环
2、境 equilibrium state 平衡状态 process 过程 interaction 相互作用 Turbine 汽轮机 piston cylinder device 活塞-缸装置 temperature 温度 pressure 压力 absolute pressure 绝对压力 relative pressure 相对压力 gage pressure 表压力 vacuum pressure 真空度 atmospheric pressure 大气压力 reciprocal 倒数 mass 质量，物质,1.1 热力系统 Thermodynamic System,1. System（热力系
3、统）系统就是指被选做研究对象的物体或空间。（ A quantity of matter or a region in space chosen for study is called a system.）For example:,气缸-活塞装置 Cylinder-piston devices,汽轮机Steam turbine,Work Output,Boundary,System,Heat Absorption,Working Medium,Heat rejection,Work Output,System,Working Medium,(1) Surroundings（外界）The mass
4、 or region outside the system is called surroundings.(2) Boundary（边界）The real or imaginary surface that separates the system from its surroundings is called boundary.(3) Interactions between system and its surroundings (系统与外界间的相互作用）There are mass or energy exchange between system and its surrounding
5、s. And they must cross the boundaries.系统与外界之间有质量及能量的交换，且都必须穿越边界,2. System, Surroundings and Boundary系统、外界和边界,System Surroundings,Mass exchange Energy exchange,Mass entering or leaving the system,Energy entering or leaving the system,Energy can cross the boundary, in the form of heat and work.,(4) Ch
6、aracteristics of boundaries,Boundaries are selected subjectively 边界是人为选定的.,Boundaries can be fixed or movable. 边界可以是固定的，也可以是可移动,Boundaries can be real or imaginary.边界可以是真实的，也可以是假想的,Boundaries are selected subjectively 热力系统选取的人为性：,锅 炉boiler,汽轮机(turbine),发电机(generator),给水泵(pump),凝汽器(condenser),过热器(reh
7、eater),Only work exchange,Only heat exchange,Work and heat exchange,真实、虚构,固定、活动,fixed 、 movable,real 、,imaginary,In terms of the interaction between system and its surroundings依据系统和外界之间的相互作用,Yes NoMass ? open closed,Heat ? non-adiabatic adiabatic,Work ? with work without work,Mass, heat or work ? no
8、n-isolated isolated,3. Types of systems 热力系统分类,A closed system (a control mass 控制质量) consists of a fixed amount of mass, and no mass can cross its boundary. That is, no mass enters or leave a closed system.闭口系与外界无物质交换such as, Piston-cylinder device (汽缸-活塞装置）An open system (or a control volume 控制体积）i
9、s a properly selected region in space. Both mass and energy can cross the boundary of a control volume.开口系与外界有物质交换such as, A Water heater, a turbine and a compressor, etc,Closed system and Open system 闭口系统和开口系统,Adiabatic system is that no heat cross the boundary or heat is negligible compared with t
10、he work cross the boundary 绝热系统与外界之间无热量交换Isolated system is a special case that no mass and energy cross the boundary.孤立系统与外界之间无任何物质和能量交换,B. Adiabatic system and Isolated system 绝热系统和孤立系统,1 open system,非孤立系相关外界 孤立系,1+2 closed system,1+2+3 adiabatic closed system,1+2+3+4 isolated system,（2）In terms o
11、f internal condition of the system （依据系统的内部状况）,其它分类方式,Physical and Chemical Properties (物理化学性质),Even System 均匀系Uneven System非均匀系,Number of Working medium 工质种类,multi substance system 多元系,Single substance system 单元系,Phase 相态,Multiple Phase 多相,Single Phase 单相,1.2 State and State Properties 状态及状态参数,1. S
12、tate The state reveals the physical condition of a system. 状态：某一瞬间热力系所呈现的宏观状况2. Property （状态参数） （1）Properties are used to depict any characteristics of a system. 状态参数：描述系统宏观物理状况的物理量,简称参数 such as Pressure P （压力），temperature T（温度），volume V（体积），mass m（质量），internal energy U（热力学能），enthalpy（焓），entropy（熵），
13、 viscosity（粘度），thermal conductivity（导热系数）。,（2） Characteristics of State Properties 状态参数的特征, Properties of a state are determined by the state. If the state is specified, its properties are fixed, or vise versa. 状态确定，则状态参数也确定，反之亦然, The magnitude of the change in property is independent of the path (r
14、oute), but just depend on the initial and final states. 状态参数的积分特征：状态参数的变化量与路径无关，只与初终态有关,Mathematically：,点函数、态函数,1,2,a,b,point function,是否是状态参数？,充要条件：, Properties are functions of state, there exist total differentialfor properties 状态参数的微分特征：全微分,After a series of change, the state returns to the orig
15、inal one,then the changes in its properties are 0,Assuming z =z (x , y),dz是全微分,充要条件：,是否是状态参数？,Total differentials,Pressure p、temperature T、Specific volume v can be measured directly (1) Density and Specific Volume密度和比容 Density is defined as mass per unit volume. 密度指单位体积所含物质的多少。,3. Basic State Proper
16、ties基本状态参数,Specific volume,Specific volume is the reciprocal of density and is defined as volume per unit mass.单位质量的物质所占有的体积，用v表示。,比体积是表示物质内部分子疏密程度的状态参数。, Definition: It is defined as the force exerted by a fluid vertically on a surface of unit area.垂直作用于单位面积上的力(for solid is stress: person stand on
17、foot) Unit of pressure It has the unit of Newton per square meter （N/m2)1 Pa=1 N/m21 kPa= 103 Pa1 MPa= 106 Pa,SI Unit:,(2) Pressure 压力,绝对压力 (absolute pressure),1 bar =105 Pa=100 kPa =0.1 MPa 标准大气压 Standard atmosphere1 atm= 101325 Pa=101.325 kPa工程大气压 Engineer atmosphere 1 at=1 kgf/cm2 =9.807 N/cm2 =9
18、.807*104 Pa液柱高度 Height of liquid column 1 atm=760 mm Hg1 at =10 m H2O,Other units 其他单位,1 mmHg=1gh =133.3 Pa,Absolute pressure is the actual pressure at a given position, denoted as .绝对压力指系统中工质的真实压力。Relative pressure indicates the difference between the absolute pressure and the local atmospheric pre
19、ssure .相对压力反映绝对压力与当地大气压力的差值。, Absolute pressure and relative pressure绝对压力和相对压力, Gage Pressure and Vacuum Pressure表压与真空度,Gage pressure（表压力）is denoted as Pg 表压力：当高于大气压时，压力计显示的绝对压力超出大气压力的部分。,表压力=绝对压力-大气压力,真空度表示绝对压力低于大气压力的量值Vacuum pressure （真空度）：Pressures below atmosphere pressure. It is the pressure di
20、fference between atmospheric and system pressure when system pressure is lower than atmospheric And it is denoted as PV or H.,真空度=大气压力-绝对压力,绝对压力与相对压力,If p pb,If p pb,Vacuum pressure pv,pb,pg,p,pv,p,relative pressure,absolute pressure,Gage pressure pg,pg,Notice:,If the atmospheric pressure changes, t
21、he gage pressure may change even though the absolute pressure of the system remain constant. That is, only absolute pressure is state property. 如果大气压力发生变化，即使工质的绝对压力不变，测压计的对数也会变，所以只有绝对压力才是状态参数。Absolute pressure is used in practical calculation 工程计算中，必须选取绝对压力,Generally, the gage is put in the atmosphe
22、re, it can only measure the difference between the absolute pressure and local atmospheric pressure. It can not give out the absolute pressure. 测量压力的仪表通常处于大气环境中，不能直接 测量出绝对压力，显示的是绝对压力和当时当地大气压的差值。, Pressure Measurement 压力p的测量,Relative pressure is the value of the absolute pressure relative to the ambi
23、ent pressure. 绝对压力与环境压力的相对值相对压力,示意图,U-tube manometer,Bourdon Tube,Ambient Pressure and Atmospheric Pressure 环境压力与大气压力,指压力表所处环境,环境压力 Ambient pressure,It is a mechanical pressure measurement device and consists of a hollow metal tube bent like a hook whose end is closed and connected to a dial indicat
24、or needle.,C-Type,B. Bourdon tube （弹簧管式压力表）,As shown in the following figure，it is known that pb=101325Pa, the height difference is H=300mm mercury liquid. The gauge pressure of B is 0.2543MPa, then what is the pressure for side A, and what is the value of PgA? 已知大气压pb=101325Pa，U型管内 汞柱高度差H=300mm，气体表
25、B读数为0.2543MPa，求：A室压力pA及气压表A的读数pgA,Exercise.1 (练习1）,Solution：,The Zeroth Law of Thermodynamics 热力学第零定律（R.W. Fowler in 1931） If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. 如果两个系统分别与第三个系统处于热平衡，则两个系统彼此必然处于热平衡。,温度测量的理论基础 B 温度计,传统：冷热程度的度量。
26、感觉，导热，热容量 微观：衡量分子热运动平均动能的量度T 0.5 m w 2,(3) Temperature （温度）,By replacing the third body with a thermometer (温度计）, we can read the temperature from the thermometer.,The Zeroth Law can be restated as: Two bodies are in thermal equilibrium if both have the same temperature reading even if they are not
27、in contact. （即使两个物体不相接触，只要它们处于热平衡，则温度值相等),Equality of temperature is a necessary and sufficient condition for thermal equilibrium,i.e. no transfer of heat. （温度相等是热平衡的充要条件）,,Company Logo,为什么叫做热力学第零定律？,热力学第零定律 1931年 T 热力学第一定律 18401850年 E 热力学第二定律 18541855年 S 热力学第三定律 1906年 S基准,Temperature measurement,,C
28、ompany Logo,温度计,substance （水银，铂电阻）,characteristics （体积膨胀，阻值）,Scale 刻度,温标 Temperature scale,Reference state 基准点,处于同一热平衡状态的各个热力系，必定有某一宏观特征 彼此相同，用于描述此宏观特征的物理量 温度。,温度是确定一个系统是否与其它系统处于热平衡的物理量。,Definition of Temperature(温度的热力学定义),Temperature scale 温标,Kelvin scale 热力学温标（绝对温标）,Celsius scale 摄氏温标,Fahrenheit s
29、cale 华氏温标 (German, G. Fahrenheit, 1686-1736),Rankine scale 朗肯温标(W. Rankine, 1820-1872),Temperature 273.16 K 0.01 ,The temperature intervals on both scales are the same.,Conversion relation among temperature scales 常用温标之间的关系,,Company Logo,绝对K,摄氏,华氏F,朗肯R,100,373.15,0.01,273.16,0,273.15,-17.8,0,-273.15
30、,212,671.67,37.8,100,0,32,-459.67,0,459.67,491.67,冰熔点,水三相点,盐水熔点,发烧,水沸点,559.67,Conversion relations between temperature scales,,Company Logo,（1） Intensive properties Intensive properties are those independent of the size of a system, such as temperature, pressure and density强度参数:与质量的多少无关的参数，不具有可加性 .,
31、4. Intensive and Extensive Properties强度参数和广延参数,Extensive properties are those whose values depend on the size or extent of the system. 广延参数:与物质的量有关的参数，具有可加性,(2) Extensive properties 广延参数,such asmass, volume, internal energy and enthalpy如 质量m、容积 V、内能 U、焓 H、,Specific properties 比参数:,Specific propertie
32、s is extensive properties per unit mass.比参数是单位质量的广延参数,比容,比内能,比焓,比熵,Intensive and Extensive Properties 强度参数与广延参数,速度,动能,高度,位能,内能,温度,（Intensive）,（Intensive）,Velocity,Kinetic Energy,Height,Potential Energy,Temperature,Internal Energy,（Intensive）,（Extensive）,（Extensive）,（Extensive）,(1) Definition A syste
33、m in equilibrium experiences no changes with time when it is isolated from its surroundings. 所谓平衡状态就是指在没有外界影响的情况下，系统的状态不随时间而发生变化。,1. Equilibrium State（平衡状态）,1.3 Equilibrium State and State Postulate 平衡状态和状态公理,In an equilibrium state there are no unbalanced potentials (or driving forces)平衡状态下，系统内外不存在
34、不平衡势差（推动力 B. A system is not in thermodynamic equilibrium unless the condition of all the relevant types of equilibrium are satisfied.,(2) How to fulfill thermodynamic equilibrium? 如何实现热力学平衡？,热平衡（Thermal equilibrium ） If the temperature is the same throughout the entire system.,热不平衡势Unbalanced poten
35、tials,温差 Temperature differential,力平衡 (Mechanical equilibrium )If there is no change in pressure at any point of the system with time.,压差 Pressure differential,力不平衡势Unbalanced potentials,Phase equilibrium（相平衡） If a system involves two phases, when the mass of each phase reaches an equilibrium level
36、and stays there ,it is in phase equilibrium. Chemical equilibrium (化学平衡 ）If no chemical reaction occur, that is, the chemical composition does not change with time, a system is in chemical,温差 热不平衡势 压差 力不平衡势相变 相不平衡势化学反应 化学不平衡势,平衡的本质：不存在不平衡势,In an equilibrium state there are no unbalanced potentials,(
37、3) Equilibrium & Steady (平衡与稳定),,Company Logo,Steady just means the properties do not vary with time. 稳定仅仅意味着参数不随时间变化,Stable but existing unequibrium potential 稳定但存在不平衡势差,去掉外界影响，则状态变化,若以（热源+铜棒+冷源）为系统，又如何？,Steady does not mean in equilibrium, but equilibrium must be steady. 稳定不一定平衡，但平衡一定稳定,(4) Equili
38、brium & Even (平衡与均匀),,Company Logo,平衡：时间上 均匀：空间上,平衡不一定均匀，单相平衡态则一定是均匀的 Substances in equilibrium does not mean theyre even, however, a single phase substance at equilibrium state must be even,(1) The equilibrium state of a system can be described by a set of properties.系统的平衡状态可以用确定的参数来描述However, give
39、n a certain number of properties is sufficient to fix a state.,2. The State Postulate 状态公理,想确切描述某个热力系， 是否需要所有状态参数？,The state of a simple comressible system can be completely specified by two independent properties.确定简单可压缩系统的状态仅需要两个彼此独立的状态参数,(2)The State Postulate,Number of independent properties =不平
40、衡势差数 独立参数数目N =能量转换方式的数目=各种功的方式 + 热量= n+1,状态公理,最重要的系统,只交换热量和一种准静态的容积变化功,容积变化功,压缩功膨胀功,简单可压缩系统 Simple compressible system,Moving Boundary Work,Compression Work,Expansion Work,A simple compressible system is a system in the absence of electrical magnetic, gravitational motion and surface tension effects
41、.,Two independent properties: If one property can be varied while the other one is held constant.(eg. P and T are independent properties for single phase systems, but are dependent properties for multiphase systems.),For Adiabatic Simple Compressible System 绝热简单可压缩系统 N = ?,Not all properties are ind
42、ependent of each other, if two independent properties are known, then other properties of the same state can be determined.各状态参数不是互相独立的，只要知道二个状态参数就可以确定系统的状态。,3. Equation of State 状态方程式,The relationship between properties is called Equation of State (E.O.S) .Narrowly speaking, the relation between p,
43、v,T is called E.O.S.状态方程 基本状态参数（p,v,T)之间的关系,Equation of state 状态方程,For Simple compressible system：N = 2,F( p,v,T)=0P=f(T,v) T=f(P,v) v=f(P,T),座标图 diagram,,Company Logo,For simple compressible system, N=2 (简单可压缩系统 N=2，) 平面坐标图,p,v,1）系统任何平衡态可表示在坐标图上,2）过程线中任意一点为平衡态,3）不平衡态无法在图上用实线表示,常见p-v图和T-s图,2,1,1.4 P
44、rocess and Cycles 过程与循环,平衡状态 Equilibrium state,状态不变化 No change in state,能量不能转换 No energy transformation occurs,Non-equilibrium state 非平衡状态,无法简单描述 Cant be described simply,1. Quasi-static or Quasi-equilibrium process 准静态过程,（1） Process and path（过程和路径）Any change that a system undergoes from one equilib
45、rium state to another is called a process.热力过程：工质从一个平衡状态过渡到另一个平衡状态所经历的全部 状态的总和。路径: The series of states through which a system passes during a process is called the path of the process.,Process 一般过程,p1 = p0+the weight of the heavy block,p，T,p0,T1 = T0,Take the heavy block away,Finally,p2 = p0,T2 = T
46、0,p,v,1,2,.,.,准静态过程 Quasi-static process,p1 = p0+重物,p，T,p0,T1 = T0,假如重物有无限多层,每次只去掉无限薄一层,p,v,1,2,.,.,.,系统随时接近于平衡态,(2) Quasi-static or Quasi-equilibrium process准静态过程,When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times, it is calle
47、d a quasi-static or quasi-equilibrium process.在无限小势差推动下的由连续平衡态组成的过程，就是准静态过程。,准静态过程有实际意义吗？ Is it applicable?,,Company Logo,既是平衡，又是变化,既可以用状态参数描述，又可进行热功转换?,疑问：理论上准静态应无限缓慢，工程上怎样处理？,准静态过程的工程条件,,Company Logo,破坏平衡所需时间 （外部作用时间）,恢复平衡所需时间 （驰豫时间）,有足够时间恢复新平衡 准静态过程,Relaxation time,A quasi-equilibrium process can be viewed as a sufficiently slow process.,准静态过程的工程应用,,Company Logo,For example：活塞式内燃机 2000转/分曲柄 2冲程/转，0.15米/冲程,活塞运动速度=20002 0.15/60=10 m/s,压力波恢复平衡速度（声速）350 m/s,破坏平衡所需时间 （外部作用时间）,
