1. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
The Classical Second Law of Thermodynamics
April 17, 2012
Prof. Sanghee Kim
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

2. processes proceed in a certain direction
First Law : energy conservation in any ordinary process
(no restriction on the direction of heat and work flow)
ex) A hot cup of coffee cools by virtue of heat transfer to the surroundings,
but heat will not flow from the cooler surroundings to the hotter cup of coffee.
processes proceed in a certain direction
Second Law : existence of such a restriction
(difference in quality bwn heat & work )
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

3. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.1 Heat Engines and Refrigerators
Fig 7.1 : A system that undergoes a cycle involving work and heat.
→ Heat Engine
- Heat Engine : work Cycle ( Q : in, W : out)
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

4. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
열전달만으로
두과정이 하나의
사이클을 완성할 수 없음
Fig7.2 : An example showing the impossibility of completing a cycle by transferring heat from a low-temperature body to a high-temperature body
→ Refrigerator (Heat Pump)
- Refrigerator : work Cycle (TL → TH, W : in)
(Heat Pump) QL
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

5. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
단순열기관
작동물질(working fluid)
: 열을 받거나 방출하는 물질
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

6. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
물이작동유체인 열기관
저온으로 전달되는 열량
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

7. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Thermal Efficiency of a Heat Engine
(7.1)
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

8. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

9. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

10. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Refrigeration Cycle
냉매로부터 열이 외부로 전달
일을 입력받아
저온에서 고온으로
열전달 실현
냉동공간에서 저온접점으로 QL만큼 전달되고
고온접점에서 QH만큼 전달
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

11. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Refrigerator
(7.2)
Thermal Reservoir : heat can be transferred indefinitely without change in the temperature of the reservoir (열저장조: 저장조의 온도변화없이 무한정으로 열교환/열저장조의 온도는 항상 일정)
- from Source(발열원) or Sink (흡열원)
ex) atmosphere , ocean
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

12. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

13. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

14. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.2 The Second Law of Thermodynamics
Kelvin-Planck Statement
It is impossible to construct a device that will operate in a cycle and produce no effect other than the raising of a weight and the exchange of heat with a single reservoir.
(M.Planck, 1897)
Es is unmoeglich, eine ~
100%일로 만드는 것은 불가능
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

15. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Clausius Statement
It is impossible to construct a device that will operate in a cycle and produce no effect other than the transfer of heat from a cooler body to a hotter body.
(Clausius)
저온에서 고온으로 열전달시 외부에서
일의 입력없이 저온의 열이 고온으로 가는
것을 불가능
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

16. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Equivalence of the two statements =0
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

17. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Perpetual-motion machine of the second kind
QL이 나와야 하는데
그대로 재활용 됨으로 Kelvin에 위배
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

18. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.3 The Reversible Process
Reversible Process
: A process that once having taken place can be reversed and in so doing leave no change in either system or surroundings.
Irreversible process
Reversible process
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

19. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.4 Factors that Render Processes Irreversible
Reversible Process
- frictionless mechanical process
- frictionless adiabatic state change
Irreversible Process
: impossible to return to original state (All Natural Process)
- Friction
- Unrestrained Expansion
- Heat transfer Through a Finite Temperature Difference
- Mixing of Two Different Substances
- Other Factors
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

20. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Friction
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

21. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Unrestrained expansion
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

22. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Mixing
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

23. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
Internally Reversible
Externally Irreversible
Reversible
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

24. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.5 The Carnot Cycle - Reversible
: the most efficient cycle that can operate between two constant-temperature reservoirs
가역과정에서 가장 효율이 높은 사이클
1 : rev. isothermal process, QH is transferred to the system
2 : rev. adiabatic process, Working Fluid : TH→TL
3 : rev. isothermal process, QL is rejected from the system
4 : rev. adiabatic process, Working Fluid : TL→TH
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

25. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
가역등온
가역단열
가역단열압축
가역등온
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

26. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
단열팽창시 열이 떨어지나
온도를 일정하게 유지하면서 팽창시킴
단열압축시 열이 생성되나
그 열을 빼주면서 압축시킴 저온
내열기관/디젤기관
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

27. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.6 Two Propositions Regarding the Efficiency of Carnot Cycle
First Proposition
Second Proposition
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

28. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.7 The Thermodynamic Temperature Scale
Carnot 사이클은 온도만의 함수
Carnot 사이클의 효율과 절대온도의 관계로 표시가능
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

29. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.8 The Ideal-Gas Temperature Scale
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

30. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

31. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

32. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

33. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
이상기체의 Carnot 사이클
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

34. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
압축 V4<V3
비체적 감소
팽창 V2>V1
비체적 증가
①→②
정온가열
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

35. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
단열팽창
②→③ *
정온방열
③→④
단열압축
④→① *
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

36. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.9 Ideal vs. real machines
가역(Carnot)사이클
실제열기관/냉동기/열펌프
 효율이 낮음
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

37. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

38. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

39. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

40. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

41. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition
7.10 Engineering Applications
Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition

42. Sonntag & Borgnakke / Fundamentals of Thermodynamics, 7th Edition