1、Chapter One Basic Concepts,Engineering Thermodynamics,Jilin University Thermal engineering department,2019/6/27,1,Lecturer主讲人：李明 Thermal Energy Department of CAE 汽车工程学院热能工程系 Tel.：85095196 E-mail:,System, surroundings, and boundary., 1-1 Thermodynamic System,Closed system (Control mass )Control volum
2、e(open system),Jilin University Thermal engineering department,2019/6/27,2,热力系统选取的人为性,锅 炉,汽轮机,发电机,给水泵,凝汽器,过热器,只交换功,只交换热,既交换功 也交换热,3,Jilin University Thermal engineering department,2019/6/27,Mass cannot cross the boundaries of a closed system, but energy can., 1-1 Thermodynamic System,Jilin Universit
3、y Thermal engineering department,2019/6/27,4,Jilin University Thermal engineering department,2019/6/27,4,Jilin University Thermal engineering department,2019/6/27,热力系统分类,以系统与外界关系划分：,有 无 是否传质 开口系 闭口系,是否传热 非绝热系 绝热系,是否传功 非绝功系 绝功系,是否传热、功、质 非孤立系 孤立系,5,Jilin University Thermal engineering department,2019/
4、6/27,A control volume may involve fixed, moving; real, and imaginary boundaries., 1-1 Thermodynamic System,Jilin University Thermal engineering department,2019/6/27,6,1 开口系,1-1 热力系统,非孤立系相关外界 孤立系,1+2 闭口系,1+2+3 绝热闭口系,1+2+3+4 孤立系,7,Jilin University Thermal engineering department,2019/6/27,The thermodyn
5、amic state of a system is defined by specifying values of a set of measurable properties sufficient to determine all other properties. For fluid systems, typical properties are pressure, volume and temperature., 1-2 The Concept of “State”,Jilin University Thermal engineering department,2019/6/27,8,A
6、 process between states 1 and 2 and the process path., 1-2 The Concept of “State”,Jilin University Thermal engineering department,2019/6/27,9,1-2 状态和状态参数,状态：某一瞬间热力系所呈现的宏观状况,状态参数：描述热力系状态的物理量,状态参数的特征：,1、状态确定，则状态参数也确定，反之亦然,2、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,3、状态参数的微分特征：全微分,State and state properties,10,
7、Jilin University Thermal engineering department,2019/6/27,强度参数与广延参数,强度参数：与物质的量无关的参数如压力 p、温度T,广延参数：与物质的量有关的参数可加性如 质量m、容积 V、内能 U、焓 H、熵S,比参数：,比容,比内能,比焓,比熵,单位：/kg /kmol 具有强度参数的性质,Intensive properties,Extensive properties,11,Jilin University Thermal engineering department,2019/6/27,状态参数的积分特征,状态参数变化量与路径无关
8、，只与初终态有关。,数学上：,点函数、态函数,1,2,a,b,例：温度变化,山高度变化,point function,12,Jilin University Thermal engineering department,2019/6/27,状态参数的微分特征 Differential Characteristics,设 z =z (x , y),dz是全微分,充要条件：necessary and sufficient condition,可判断是否是状态参数,Total differentials,13,Jilin University Thermal engineering departme
9、nt,2019/6/27,Absolute, gage, and vacuum pressures., 1-2 The Concept of “State”,Jilin University Thermal engineering department,2019/6/27,14,Comparison of temperature scales. Celsius scale Kelvin scale Fahrenheit scale Rankine scale, 1-2 The Concept of “State”,Jilin University Thermal engineering dep
10、artment,2019/6/27,15,温度T 的一般定义,传统：冷热程度的度量。感觉，导热，热容量,微观：衡量分子平均动能的量度T 0.5 m w 2,1) 同T , 0.5mw 2 不同，如碳固体和碳蒸气,2) 0.5mw 2总0, T 0, 1951年核磁共振法对氟化锂晶体的实验发现负的开尔文温度,3) T=0 0.5mw 2=0 分子一切运动停止，零点能,16,Jilin University Thermal engineering department,2019/6/27,The Zeroth Law of Thermodynamics,如果两个系统分别与第三个系统处于热平衡，则两
11、个系统彼此必然处于热平衡。,If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.,17,Jilin University Thermal engineering department,2019/6/27, 1-3 Equilibrium State,在不受外界影响的条件下（重力场除外），如果系统的状态参数不随时间变化，则该系统处于平衡状态。 A system in thermodynamic equilibrium sat
12、isfies: mechanical equilibrium (no unbalanced forces) thermal equilibrium (no temperature differences) chemical equilibrium,Jilin University Thermal engineering department,2019/6/27,18,Types of Equilibrium,1、热平衡Thermal equilibrium : if the temperature is the same throughout the entire system,温差 Temp
13、erature differential,热不平衡势Unbalanced potentials,19,Jilin University Thermal engineering department,2019/6/27,2、力平衡Mechanical equilibrium : if there is no change in pressure at any point of the system with time. The variation of pressure as a result of gravity in most thermodynamic system is relative
14、ly small and usually disregarded,Types of Equilibrium,压差 Pressure differential,力不平衡势Unbalanced potentials,20,Jilin University Thermal engineering department,2019/6/27,3、相平衡Phase equilibrium : when the mass of each phase reaches an equilibrium level and stays there,4、化学平衡Chemical equilibrium : if its
15、 chemical composition does not change with time. That is, no chemical reactions occur.,State Postulate 状态公理The thermodynamics state of a simple compressible system is completely specified by two independent , intensive properties （强度参数：将系统人为地划分为若干部分，对各部分来说，如某一性质仍保持系统原来的数值，这一性质即为强度性质）., 1-3 Equilibri
16、um State,Jilin University Thermal engineering department,2019/6/27,21,平衡Equilibrium与稳定Steady,稳定：参数不随时间变化,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？,稳定不一定平衡，但平衡一定稳定,22,Jilin University Thermal engineering department,2019/6/27,平衡Equilibrium与均匀Even,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,23,Jilin Universi
17、ty Thermal engineering department,2019/6/27,为什么引入平衡概念？,如果系统平衡，可用一组确切的参数（压力、温度、比体积）描述,但平衡状态是死态，没有能量交换,能量交换,状态变化,破坏平衡,如何描述,24,Jilin University Thermal engineering department,2019/6/27,状态方程、坐标图,平衡状态可用一组状态参数描述其状态,状态公理：对组元一定的闭口系，独立状态参数个数 N=n+1,想确切描述某个热力系，是否需要所有状态参数？,25,Jilin University Thermal engineerin
18、g department,2019/6/27,状态公理State postulate,闭口系：,而不平衡势差彼此独立, 独立参数数目N=不平衡势差数=能量转换方式的数目=各种功的方式+热量= n+1,n 容积变化功、电功、拉伸功、表面张力功等,26,Jilin University Thermal engineering department,2019/6/27,简单可压缩系统的独立变量数,简单可压缩系统：N = n + 1 =2,绝热简单可压缩系统 N = ?,只交换热量和一种准静态的容积变化功,The state of a simple compressible system is com
19、pletely specified by two independent properties,27,Jilin University Thermal engineering department,2019/6/27,状态方程Equation of state,简单可压缩系统：N = 2,状态方程 基本状态参数（p,v,T)之间的关系,28,Jilin University Thermal engineering department,2019/6/27,The P-V diagram of a compression process., 1-3 Equilibrium State,Jilin
20、 University Thermal engineering department,2019/6/27,29,系统与外界无能量和物质变化：thermal equilibrium+force equilibrium+chemical equilibrium,座标图diagram,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,2,1,30,Jilin University Thermal engineering department,2019/6/27, 1-4 Gas Equ
21、ation of State,This implies: (1) very little molecular interaction (p 0),and (2) molecules are point masses, i.e., zero volume.,Gas equation of state,For 1kg,For 1mol,The ideal gas equation of state,Jilin University Thermal engineering department,2019/6/27,31,What is standard state？ p0/Vm,0/T0,The u
22、niversal gas constant,M = Molecular weight, kg/kmol, 1-4 Gas Equation of State,Jilin University Thermal engineering department,2019/6/27,32,Example1-2 Known,assumptions,find,solution,result,2019/6/27,Jilin University Thermal engineering department,33,A gas does a differential amount of work W as it
23、forces the piston to move by a differential amount ds., 1-5 Quasi-static Process and reversible process,Jilin University Thermal engineering department,2019/6/27,34,突然去掉重物作用力与逐步撤力的差异,Only “infinitesimal” unbalanced forces exist, so that the process can be viewed as taking place in a series of “quasi
24、-equilibrium” states. (The term quasi can be taken to mean “as if”.),For this to be true the process must be slow in relation to the time needed for the system to come to equilibrium internally., 1-5 Quasi-static Process and reversible process,Jilin University Thermal engineering department,2019/6/2
25、7,35,准静态过程有实际意义吗？,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？,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）,Relaxation time,有足够时间恢复新平衡 准静态过程,36,Jilin University Thermal engineering department,2019/6/27,准静态过程的容积变化功,p,p外,f,初始：pA = p外A +f,A,如果 p外微小,可视为准静态过程,dl,以汽缸中mkg工质为系统,mkg工质发生容积变化对外界作的功,W = pA dl =pd
26、V,1kg工质,w =pdv,dl 很小，近似认为 p 不变,Moving Boundary Work,37,Jilin University Thermal engineering department,2019/6/27,准静态过程的容积变化功,p,p外,2,mkg工质：,W =pdV,1kg工质：,w =pdv,1,注意：,上式仅适用于准静态过程,38,Jilin University Thermal engineering department,2019/6/27,准静态容积变化功的说明,p,V,.,1,2,.,2） p-V 图上用面积表示,3）功的大小与路径有关，过程量Path fu
27、nction,4）统一规定：dV0，膨胀 对外作功（正） dV0，压缩 外内作功（负）,5）适于准静态下的任何工质（一般为流体）,6）外力无限制，功的表达式只是系统内部参数,7）有无f，只影响系统功与外界功的大小差别,39,Jilin University Thermal engineering department,2019/6/27,可逆reversible过程的定义,系统经历某一过程后，如果能使系统与外界同时恢复到初始状态，而不留下任何痕迹，则此过程为可逆过程。,A process that can reversed without leaving any trace on the su
28、rroundings. That is, both the system and the surroundings are returned to their initial states at the end of the reverse process.,可逆过程只是指可能性，并不是指必须要回到初态的过程。,40,Jilin University Thermal engineering department,2019/6/27,可逆过程的实现,准静态过程 + 无耗散效应 = 可逆过程,无不平衡势差,通过摩擦使功 变热的效应(摩阻，电阻，非弹性变性，磁阻等）,不平衡势差 不可逆根源耗散效应,
29、耗散效应,irreversibility,Dissipative effect,41,Jilin University Thermal engineering department,2019/6/27,Heat transfer,常见的不可逆过程,不等温传热,T1,T2,T1T2,Q,节流过程(阀门）,p1,p2,p1p2,normal irreversible processes,Throttler,42,Jilin University Thermal engineering department,2019/6/27,常见的不可逆过程,混合过程,自由膨胀,真空,normal irrever
30、sible processes,Unrestrained expansion,Mixing process,43,Jilin University Thermal engineering department,2019/6/27,引入可逆过程的意义, 准静态过程是实际过程的理想化过程，但并非最优过程，可逆过程是最优过程。, 可逆过程的功与热完全可用系统内工质的状态参数表达，可不考虑系统与外界的复杂关系，易分析。, 实际过程不是可逆过程，但为了研究方便，先按理想情况（可逆过程）处理，系统参数加以分析，然后考虑不可逆因素加以修正。,44,Jilin University Thermal engin
31、eering department,2019/6/27,A reversible process for a system is defined as a process that, once having taken place, can be reversed, and in so doing leaves no change in either the system or surroundings.,In other words the system and surroundings are returned to their original condition before the
32、process took place.,In reality, there are no truly reversible processes; however, for analysis purposes, one uses reversible to make the analysis simpler, and to determine maximum theoretical efficiencies., 1-5 Quasi-static Process and reversible process,Jilin University Thermal engineering departme
33、nt,2019/6/27,45,45,Jilin University Thermal engineering department,2019/6/27, 1-6 The work of quasi-static process,Interactions,Jilin University Thermal engineering department,2019/6/27,46,功的力学定义:The product of a force and the distance through which this force acts,功的热力学定义:当热力系与外界发生能量传递时，如果对外界的唯一效果可
34、归结为取起重物，此即为热力系对外作功。Work is done by a system if the sole effect on the surroundings could be the raising of a weight.,46,Jilin University Thermal engineering department,2019/6/27,Deformation of the system boundary, 1-6 The work of quasi-static process,Jilin University Thermal engineering department,2
35、019/6/27,47,Evaluating the work .Integral for a quasi-static process., 1-6 The work of quasi-static process,Jilin University Thermal engineering department,2019/6/27,48, 1-7 Heat,A resistor heating water,Evaluating the heat .Integral for a quasi-static process.,Jilin University Thermal engineering d
36、epartment,2019/6/27,49,Heat is defined as the form of energy that is transferred between two systems (or its surroundings) by virtue of temperature difference. 热量定义：热量是热力系与外界相互作用的另一种方式，在温度的推动下，以微观无序运动方式传递的能量。,引入“熵”,热量与容积变化功,能量传递方式 容积变化功 传热量,性质 过程量 过程量,推动力 压力 p 温度 T,标志 dV , dv dS , ds,公式,条件 准静态或可逆 可逆
37、,50,Jilin University Thermal engineering department,2019/6/27,熵（ Entropy）的定义,reversible,比参数 kJ/kg.K,ds: 可逆过程 qrev除以传热时的T所得的商,清华大学刘仙洲教授命名为“熵”,广延量 kJ/K,51,Jilin University Thermal engineering department,2019/6/27,熵的说明explanation,1、熵是状态参数,3、熵的物理意义：熵体现了可逆过程传热的大小与方向,2、符号规定,系统吸热时为正 positive Q 0 dS 0 系统放热时
38、为负 negative Q 0 dS 0,4、用途：判断热量方向计算可逆过程的传热量,52,Jilin University Thermal engineering department,2019/6/27, 1-8 Cyclic Processes,Jilin University Thermal engineering department,2019/6/27,53,要实现连续作功，必须构成循环,定义：力系统经过一系列变化回到初态，这一系列变化过程称为热力循环。,A system is said to have undergone a cycle if it returns to its
39、initial state at the end of the process,循环和过程Cycle and process,循环由过程构成cycle composed by processes,不可逆循环,可逆reversible,过程process,不可逆irreversible,循环,可逆循环,正循环,动力循环Power cycle,顺时针方向,净效应：对外作功,净效应：吸热,54,Jilin University Thermal engineering department,2019/6/27,2,3,4,1,v,p,2,3,4,1,v,p,2019/6/27,Jilin University Thermal engineering department,55,逆循环 reverse cycle,净效应：对内作功,净效应：放热,逆时针方向counterclockwise /anticlockwise,逆时针方向,3,2,1,3,2,1,4,4,v,p,s,T,
