工程热力学：04 第三章 理想气体的热力学能 焓 熵.ppt

1、Jilin University Thermal Engineering department,1,Engineering Thermodynamics,Chapter Three Thermodynamic Energy, Enthalpy and Entropy of the Ideal-Gas,Jilin University Thermal Engineering department,2,3-1 Thermodynamic energy and enthalpy of ideal gas,Experiment conclusion： u=f(T)thermodynamic energ

2、y is only the function of temperature,Joule experiment,Jilin University Thermal Engineering department,3,According to the constant volume process, the thermodynamic energy（u）is,enthalpy,3-1 Thermodynamic energy and enthalpy of ideal gas,Jilin University Thermal Engineering department,4,calculation o

3、f enthalpy (h) changing： According to the constant volume process,That is,enthalpy is only the function of temperature,3-1 Thermodynamic energy and enthalpy of ideal gas,Jilin University Thermal Engineering department,5,3-2 Specific heats of ideal gas,Definition：,As described in first law,For consta

4、nt,That is,volume process：,Jilin University Thermal Engineering department,6,Definition for constant pressure specific heat ：,As described in first law,3-2 Specific heats of ideal gas,Jilin University Thermal Engineering department,7,For constant pressure process ：,That is,3-2 Specific heats of idea

5、l gas,Jilin University Thermal Engineering department,8,If u=f(v,T)、 h=f(p,T)，and the specific thermodynamic energy u and specific enthalpy h of ideal gas are only the function of temperature, and it can be expressed as follows:,Compare with thermodynamic energy change and enthalpy change of the ide

6、al gas, we can get:,3-2 Specific heats of ideal gas,Jilin University Thermal Engineering department,9,That is,The temperature of unit ideal gas increase 1K in any condition, the increment of the specific thermodynamic energy is equal to its specific constant volume heat, and the increment of specifi

7、c enthalpy is equal to its specific constant pressure heat.,3-2 Specific heats of ideal gas,Jilin University Thermal Engineering department,10,The relation between specific constant volume heat and specific constant pressure heat.,According to the expression of ideal specific constant pressure heat,

8、for,so,That is,3-2 Specific heats of ideal gas,Jilin University Thermal Engineering department,11,And for,so,if,That is,3-2 Specific heats of ideal gas,Jilin University Thermal Engineering department,12,Real specific heat,Specific heat not only relate to the pressure but also relate to temperature.

9、It is usually expressed as the function of temperature according to the experiment.,The heat can be calculated by real specific heat：,Jilin University Thermal Engineering department,13,The real specific heat applies to large temperature difference and high precision.,real specific heat,Jilin Univers

10、ity Thermal Engineering department,14,Average specific heat,That is,Jilin University Thermal Engineering department,15,Heat transfer, the change in enthalpy for constant pressure process:,Heat transfer, the change in internal energy for constant volume process：,Average specific heat,Jilin University

11、 Thermal Engineering department,16,Constant specific heat - the experiment results of the specific heat at 25。,Jilin University Thermal Engineering department,17,3-3 Entropy of ideal gas,Definition of entropy:,or,Quasi-state process：,Jilin University Thermal Engineering department,18,so：,for,and：,3-

12、3 Entropy of ideal gas,Jilin University Thermal Engineering department,19,For infinitesimal process：,3-3 Entropy of ideal gas,Jilin University Thermal Engineering department,20,The entropy changing of the finite process can be the integral of the mentioned expression, for the constant specific heat:

13、,3-3 Entropy of ideal gas,Jilin University Thermal Engineering department,21,Standard state entropy,Entropy changing of the process can be calculated by standard state entropy in the condition of large temperature changing or restrict calculation requirement .,Definition:,Jilin University Thermal En

14、gineering department,22,According to the expression of entropy changing for the ideal gas,According to the definition of standard state entropy:,Standard state entropy,Jilin University Thermal Engineering department,23,3-4 Mixture of ideal gases,The state function of ideal gas also apply to mixture

15、of ideal gases ：,Mass of mixture：,Mole mass：,Definition of ideal gas mixture: no chemical reaction,Jilin University Thermal Engineering department,24,1. Partial pressure and partial volume,Summary of partial pressure：,so,Daltons law pressure of ideal gases mixture should be the summary of partial pr

16、essure of the components,Definition of partial pressure,Jilin University Thermal Engineering department,25,Definition of partial volume,The summary of partial volumes：,so,Amagats law the volume of ideal gases mixture is the summary of the partial volume of the components.,1. Partial pressure and par

17、tial volume,Jilin University Thermal Engineering department,26,For certain component i，the partial pressure and partial volume can be expressed as follows:,We can conclude：,That is the relation between partial pressure and total pressure and partial volume and total volume。,1. Partial pressure and p

18、artial volume,Jilin University Thermal Engineering department,27,2. Components of mixture,The expression of the components of mixture,mass fraction：,mole fraction：,Volume fraction：,so,Jilin University Thermal Engineering department,28,Relationships among the different fractions,for,for,for,so,so,so,

19、Jilin University Thermal Engineering department,29,3. The density, molar mass and equivalent gas constant of mixture,According to the definition of density, the density of mixture should be:,That is,for,so,Jilin University Thermal Engineering department,30,According to the definition of molar mass，t

20、he molar mass of mixture should be:,that is：,for,so,3. The density, molar mass and equivalent gas constant of mixture,Jilin University Thermal Engineering department,31,The equivalent gas constant of mixture should be:,that is：,and,so we can get,3. The density, molar mass and equivalent gas constant

21、 of mixture,Jilin University Thermal Engineering department,32,4. Thermodynamic energy and enthalpy of ideal gas mixtures,The thermodynamic energy of the mixture is the summary of components thermodynamic energy, that is,so：,Jilin University Thermal Engineering department,33,so：,According to the def

22、inition of enthalpy and Amagat law，the enthalpy of mixture of ideal gases：,4. Thermodynamic energy and enthalpy of ideal gas mixtures,Jilin University Thermal Engineering department,34,5. Specific heat of ideal gas mixtures,It can be concluded from thermodynamic energy and specific heat that：,Jilin

23、University Thermal Engineering department,35,It can be concluded from specific enthalpy and specific heat：,5. Specific heat of ideal gas mixtures,Jilin University Thermal Engineering department,36,According to the relation between specific heat and mole,and,so,5. Specific heat of ideal gas mixtures,Jilin University Thermal Engineering department,37,And so：,Substitute,so,5. Specific heat of ideal gas mixtures,