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1、Chapter 3 The Properties Of Ideal Gas,The Properties Of Ideal Gas,3-1. Ideal gas 3-2. Ideal gas equation of state 3-3. Specific heat 3-4. Internal energy and enthalpy 3-5. Entropy of the ideal gas 3-6. The mixed of ideal gas,3-1.Ideal gas,Definition: Ideal gas is an imaginary gas that obeys these re
2、lationships (or conditions): The molecules of ideal gas are elastic particles that have no volume ; There is no any force among the molecules of ideal gas; There are several equations of state , some simple and others very complex. The simplest and best known equation of state for substances in gas
3、phase is the ideal-gas equation of state.,3-1.Ideal gas,This equation of state predicts the p-v-t behavior of a gas quite accurately within some property selected region.,3-2.Ideal gas equation of state,1.Ideal gas equation of state Rg: is gas constant, unit: kJ/kg.k,3-2.Ideal gas equation of state,
4、2.Universal gas constant Rm: is universal gas constant, unit: kJ/kmol.k Rm=8.314 kJ/kmol.k,3-2.Ideal gas equation of state,3. Example,3-3.Specific heat,1.Definition: Specific heat is the amount of energy that crosses the boundary of a system containing unit mass of matter so that its temperature cha
5、nges by 1 degree. Here , unit mass mean: per kg, m3, kmol ; So specific heat unit: kJ/kg.K , kJ/m3.K , kJ/kmol.K ; It depend on : state, the matter , process , unit .,3-3.Specific heat,Specific heat at constant volume and pressure are: From:,3-2.Specific heat,We can get: If is ideal gas :,3-2.Specif
6、ic heat,for ideal gas we can get :,3-2.Specific heat,The relationship between cp, cv:,So : cp cv if:,3-2.Specific heat,We can get:,For actul gas :,3-3.Specific heat,2.The calculation of specific heat Average specific heat calculation: c=f(t, p) there is no potential energy for idear gas , so : c=f(t
7、) if : c=a+bt+ct2,3-3.Specific heat,c=f(t),A,t1 B,t2 D,t,O,F,E,c,q,q,H,G,cm,3-3.Specific heat,Because t1, t2 are change, so let t1=0,3-3.Specific heat,See attach table 4, 5,6,3-3.Specific heat,Average specific heat with line relationship: c=f(t) if : c=a+bt,3-3.Specific heat,c=a+bt,A,t1 B,t2 D,t,F,E
8、,c,q,q,H,G,cm,3-3.Specific heat,Average specific heat with line relationship:,Let t1=0, t2=t then,See attach table 7,3-4.Internal energy and enthalpy of ideal gas,Ideal gas in first law:,3-5.Entropy of the ideal gas,1.Entropy is property,(Ideal gas & Reversible process),(Ideal gas & Reversible proce
9、ss),3-5.Entropy of the ideal gas,2.Calculation of entropy deference,3-5.Entropy of the ideal gas,If T is small, and cp, cv have fixed value, then:,3-5.Entropy of the ideal gas,Example:,3-6. The mixed of ideal gas,1.Composition of ideal gas mixture To determine the properties of a mixture, we need to
10、 know the composition of the mixture as well as the properties of the individual components. There are three ways to describe the composition of mixture: Mass Fractions, Volume Fractions, Molar Fractions,3-6. The mixed of ideal gas,2.Mass Fractions,3-6. The mixed of ideal gas,3. Volume Fractions,3-6
11、. The mixed of ideal gas,3. Molar Fractions,3-6. The mixed of ideal gas,5.Daltons law of additive pressures for mixture of ideal gases,P=pi,Gas 1 V, T,+,+,Daltons law: The pressure of a gas mixture is equal to the sum of the pressure each gas would exert if it existed alone at the mixture temperatur
12、e and volume.,p1,Gas 2 V, T,p2,Gas i V, T,pi,=,Gas mixture V, T,P=pi,3-6. The mixed of ideal gas,5.Amagats law of additive volumes for mixture of ideal gases,V=Vi,Gas 1 p, T,+,+,Amagats law: The volume of a gas mixture is equal to the sum of the volumes each gas would occupy if it existed alone at t
13、he mixture temperature and pressure.,V1,Gas 2 p, T,V2,Gas i p, T,Vi,=,Gas 1 p, T,V1,Gas 2 p, T,V2,Gas i p, T,Vi,Gas mixture p, T,V=Vi,3-6. The mixed of ideal gas,6.Relationship of fractions,3-6. The mixed of ideal gas,6.Relationship of fractions,3-6. The mixed of ideal gas,7.The specific heat, internal energy, enthalpy, entropy of the mixture,
