第二章理想气体的性质Chapter2PropertiesofIdealGas.ppt

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1、第二章 理想气体的性质Chapter 2.Properties of Ideal Gas,2.1 理想气体的状态方程 Equation of State for Ideal Gas 2.2 理想气体的比热 Specific Heat of Ideal Gas2.3 混合理想气体的性质 Properties of Ideal Gas Mixtures,工程热力学的两大类工质,1、理想气体（ideal gas）,可用简单的式子描述如汽车发动机和航空发动机以空气为主的燃气、空调中的湿空气等,2、实际气体（real gas）,不能用简单的式子描述，真实工质 如火力发电的水和水蒸气、制冷空调中制冷工质等

2、,实际气体的特点Characteristics of real gases includes:由大量分子组成(consists of large quantities of molecular)分子做无规则运动(molecules take random movement continuously)分子间有作用力(interaction force among molecules)分子本身有体积(the volume of molecules)以上特点决定了实际气体的性质很复杂。,1.两点假设(Assumptions)忽略分子的容积(The volume of the gas molecule

3、 is negligible.)。忽略分子之间的作用力(The interaction forces between molecules are negligible),3.1 理想气体的状态方程（Equation of State for Ideal Gas）,1.分子之间没有作用力 2.分子本身不占容积,但是,当实际气体 p 很小,V 很大,T不太低时,即处于远离液态的稀薄状态时,可视为理想气体。,理想气体模型 Model of ideal-gas,现实中没有理想气体,哪些气体可当作理想气体,T常温，p7MPa的双原子分子,理想气体,O2,N2,Air,CO,H2,如汽车发动机和航空发动机

4、以空气为主的燃气等,三原子分子（H2O,CO2)一般不能当作理想气体,特殊可以，如空调的湿空气，高温烟气的CO2,2.理想气体状态方程式Equation of state for ideal gas(1).For 1 1kg working gas,Pv=RTP:绝对压力(absolute pressure)，Pa。v:比容(specific volume),m3/kg。T：热力学温度(Kelvin Temperature),K。R：气体常数(Gas constant)与气体的种类有关。(2)For m kg working gas,mPv=mRT or PV=mRT,摩尔质量(molar m

5、ass):the mass of 1mol substance(1mol 物质的质量)，M 摩尔体积(molar volume):the volume of 1mol substance(1mol物质占有的体积)，Vm。阿伏假德罗定律(Avogadros hypothesis):在同温同压下，各种气体的摩尔体积都相等。,在标准状况下,(3)For 1mol working gas,Vm=Mrv/1000，Mr：分子量。MrPv=MrRT PVm=RmT,Vm常用来表示数量,Rm与R的区别,Rm通用气体常数,R气体常数,M-Molar mass,例如,Universal Gas constant

6、,与气体种类无关,Gas constant,与气体种类有关,(4)For n Mole working gas For n mol gas,PV=nRmT,理想气体(Definition of Ideal Gas)：,凡遵循克拉贝龙(Clapeyron)方程的气体,四种形式的克拉贝龙方程：,Rm 与R,摩尔容积Vm,状态方程(E.O.S),统一单位,计算时注意事项实例 Attentions:,V=1m3的容器有N2，温度为20，压力表读数1000mmHg，pb=1atm，求N2质量。,1）,2）,3）,4）,The volume of the room is V=4m 5m 6m=120 m3

7、The mass of air in a room is determined from the ideal gas relation to be,Example.Determine the mass of air in a room whose dimensions are 4m 5m 6m at 100kPa and 25Solution The mass of air in a room is to be determined.Analysis Air at specified conditions can be treated as an ideal gas.From table,th

8、e gas constant of air is R=0.287 kJ/kg.K and the absolute temperature is T=25+273.15=298.15 K.,3.2 比热和热容Specific Heats and Heat Capacity 1.比热容（比热）的定义 Definition of Specific heat 将单位物量的物质温度升高1K所需加入的热量。The energy required to raise the temperature of a unit quantity of a substance by one degree,2.基于不同物

9、量单位的三种比热(Three kinds of Specific heats based on different quantity units)质量比热容(Specific heat based on mass)1kg物体温度1K升高1K所吸收的热量，记作c，单位为 J/kgK It is denoted as c and its unit is J/kgK),(2)摩尔比热容(Specific heat based on mole)：Mc kJ/kmolK 1mol物体温度1K升高1K所吸收的热量，记作 Mc 单位为 kJ/kmolK)。(3)体积比热容(Specific heat bas

10、ed on Volume at standard condition)c kJ/Nm3K(标准状态下1m3(1Nm3)物体温度升高1K所吸收的热量，记作c 单位为 kJ/m3K)。,比热容,c:质量比热容,Mc:摩尔比热容,C:容积比热容,Mc=Mc=22.414C,The relationship among the three specific heat,T,s,(1),(2),1 K,比热容是过程量还是状态量?,c1,c2,用的最多的某些特定过程的比热容,定容比热容,定压比热容,3.定压比热和定容比热 Specific heat at constant pressure and at c

11、onstant volume For a constant pressure process:or,and for a constant volume process:,or,迈耶公式Mayers formula,令,比热比,理想气体的定压和定容比热容的关系 The relation between two specific heat of Ideal gases,4.理想气体比热容的计算,温度是影响比热容的主要因素(Temperature is the main factor that has influence on the specific heat）,(1)真实比热 Actual sp

12、ecific heat,根据实验结果整理,(2)平均比热 Mean specific heat,t,t2,t1,c(cp,cv),附表3，4，5，6,c=f(t),摄氏,求O2在100-500平均定压热容,分子运动论,(3)定比热容 Constant specific heat,运动自由度,当温度变化不大时，可认为比热容为常数，与温度无关，此时也是常数。When the change in temperature is not so large,the influence of temperature on specific heat is negligible.,k,1.67,1.4,1.2

13、9,Exercises：,1.Calculate the constant specific heat of air based on mass.2.Calculate the mean specific heat of oxygen between 100 to 650,2.3混合理想气体的性质 Properties of Ideal Gas Mixtures,1.混合气体的分压力和道尔顿分压力定律 Component pressure and Daltons law of additive pressures（1）分压力的定义（Definition of Component pressur

14、e）假定混合气体中组成气体单独存在，并具有与混合气体相同的温度及容积时的压力。（2）道尔顿分压力定律(Daltons law of additive pressures),2.混合气体的分容积和阿密盖特分容积定律Component Volume and Amagats law additive volume（1）Definition of component volume(分容积 的定义)假定混合气体中组成气体具有与混合气体相同的温度及压力时，单独存在所占有的容积。（2）Amagats law additive volume(阿密盖特分容积定律),3.Composition of gas mi

15、xture(混合气体的成分)（1）质量成分（mass fraction）(2)容积成分（volume fraction),(3)摩尔成分（mole fraction)(4)质量成分、容积成分与摩尔成分间的换算关系（relationship between mass fraction,volume fraction and mole fraction),4.混合气体的折合分子量与气体常数 Molar mass(Average mass)and the gas constant（1）Molar mass(折合分子量)（2）Gas constant(折合气体常数),5.分压力的确定 Determine the Component pressure 6.混合气体的比热 Specific heat of gas mixture,Reading and Review(阅读和复习）Book of English version(英文版教材)Sections 2.6 on Page 8789(第8789页 第2.6节）Sections 2.92.10 on Page 98105，(第98105页 第2.92.10节）Book of Chinese version(中文版教材)Chapter 2（第二章）,