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atms 305 atmospheric thermodynamics and statics

Today's lecture topics:The Second Law of Thermodynamics and Entropy (W

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atms 305 atmospheric thermodynamics and statics

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    1. Todays lecture objectives: The Second Law of Thermodynamics and Entropy (W&H 3.7) If I need energy to create thunderstorms, how much bang for the buck can I get out of a given atmospheric environment? ATMS 305 Atmospheric Thermodynamics and Statics

    2. Todays lecture topics: The Second Law of Thermodynamics and Entropy (W&H 3.7) Types of processes The Carnot cycle entropy The temperature-entropy and skew T-ln p diagrams Generalized statement of the Second Law of Thermodynamics ATMS 305 The Second Law of Thermodynamics and Entropy

    3. First Law of Thermodynamics

    4. First Law of Thermodynamics Energy cannot be created or destroyed. It can only be changed from one form into another.

    5. First Law of Thermodynamics Conservation of Energy Says Nothing About Direction of Energy Transfer

    6. Second Law of Thermodynamics Preferred (or Natural) Direction of Energy Transfer Determines Whether a Process Can Occur

    7. Second Law of Thermodynamics Three Types of Thermodynamic Processes Natural (or Irreversible) Impossible Reversible

    8. Natural (or Irreversible) Process Physical Processes That Proceed in One Direction But Not The Other Tends Towards Equilibrium Equilibrium Only At End of Process

    9. Natural (or Irreversible) Process Examples Free Expansion of Gas

    10. Natural (or Irreversible) Process Examples Free Expansion of Gas

    11. Natural (or Irreversible) Process Examples Thermal Conduction

    12. Natural (or Irreversible) Process Examples Thermal Conduction

    13. Natural (or Irreversible) Process Examples Conversion of Potential & Kinetic into Internal Energy

    14. Natural (or Irreversible) Process Examples Conversion of Potential & Kinetic into Internal Energy

    15. Natural (or Irreversible) Process Examples Conversion of Potential & Kinetic into Internal Energy

    16. Natural (or Irreversible) Process Equilibrium Time independent Properties do not change with time

    17. Impossible Process Physical processes that do not occur naturally Process that takes system from equilibrium

    18. Impossible Process Examples Free Compression of Gas

    19. Impossible Process Examples Free Compression of Gas

    20. Impossible Process Examples Thermal Conduction

    21. Impossible Process Examples Thermal Conduction

    22. Impossible Process Examples Conversion of Potential, Kinetic and Internal Energy

    23. Impossible Process Examples Conversion of Potential, Kinetic and Internal Energy

    24. Impossible Process Cannot Occur without Input of Work

    25. Impossible Process Systems Entropy Decreases Total Entropy Increases

    26. Reversible Process Reversal in direction returns substance & environment to original states

    27. Reversible Process A conceptual process Idealized version of how things should be No processes are truly reversible

    28. Reversible Process Useful concept Helps investigate Second Law and Entropy

    29. Reversible Process Conditions that aid a reversible process Process occurs slow enough Each state of the system is in an equilibrium State variables reach equilibrium

    30. Distinction between a reversible and an irreversible process: reversible one can reverse the process and cause the system (e.g. Polly Parcel) and the environment both to return to their original condition irreversible one can reverse the process and cause the system to return to its original condition, but the environment will have suffered a change from the original condition ATMS 305 The Second Law of Thermodynamics and Entropy

    31. Nicolas Leonard Sadi Carnot French engineer and physicist A Reflection on the Motive Power of Heat (1824) Heat Engines Cyclic and Reversible Processes

    32. http://www.keveney.com/Locomotive.html ATMS 305 The Second Law of Thermodynamics and Entropy

    33. ATMS 305 The Second Law of Thermodynamics and Entropy Carnots ideal heat engine Working substance in a cylinder (Y) with insulating walls and a conducting base (B) fitted with an insulated, frictionless piston (P) Nonconducting stand (S) Infinite warm reservoir of heat (H) at constant temperature T1 Infinite cold reservoir for heat (C) at constant temperature T2

    34. ATMS 305 The Second Law of Thermodynamics and Entropy Carnots ideal heat engine (cont.) Heat is supplied to the working substance within the cylinder at (H) Heat is extracted from the working substance within the cylinder at (C) As the working substance expands (or contracts) the cylinder moves outward (or inward) and external work is done by (or on ) the engine

    35. ATMS 305 The Second Law of Thermodynamics and Entropy Carnots ideal heat engine (cont.) [A] start of cycle with working substance at T2 , piston sits on stand (S) and is pushed in, adiabatic compression, so that the substance is moved to state [B] [B] the working substance now has a temperature T1 due to the adiabatic compression in moving from [A] to [B]. The cylinder is now placed on reservoir (H) from which it extracts a quantity of heat Q1. The working substance expands isothermally at temperature T1 to point [C]

    36. ATMS 305 The Second Law of Thermodynamics and Entropy Carnots ideal heat engine (cont.) [C] cylinder is returned to the stand (S) and undergoes an adiabatic expansion until its temperature falls to T2 [D] The cylinder is now placed on reservoir (C) to which it expels a quantity of heat Q2. The working substance is compressed isothermally at temperature T2 to point [A]

    37. ATMS 305 The Second Law of Thermodynamics and Entropy

    38. ATMS 305 The Second Law of Thermodynamics and Entropy Entropy (S) In passing reversibly from one adiabat to another along an isotherm heat is absorbed or rejected, where the amount of heat Qrev depends on the temperature T of the isotherm (the subscript rev indicates that the heat is exchanged reversibly)

    39. ATMS 305 The Second Law of Thermodynamics and Entropy Entropy (S) The ratio Qrev/T is the same no matter which isotherm is chosen in passing from one adiabat to another. Therefore, the ratio Qrev/T is a measure of the difference between the two adiabats; it is called the difference in entropy (S).

    40. Entropy (S) A thermodynamic state function Similar to pressure, temperature or volume Path independent

    41. Entropy (S) A measure of the microscopic disorder of a system

    42. Entropy (S) A measure of the microscopic disorder of a system

    43. Entropy (S) A measure of the energy that is no longer available to do work

    44. ATMS 305 The Second Law of Thermodynamics and Entropy Carnot cycle A to B and C to D transformations are both adiabatic and reversible (constant entropy) In passing from B to C, the substance takes in reversibly a quantity of heat Q1 from the source at T1; the entropy of the source decreases by Q1/T1.

    45. ATMS 305 The Second Law of Thermodynamics and Entropy Carnot cycle Net change in entropy in the complete Carnot cycle is Q2/T2 - Q1/T1. However, we have shown that this difference is zero, hence, there is no change in entropy in a Carnot cycle

    46. ATMS 305 The Second Law of Thermodynamics and Entropy

    47. ATMS 305 The Second Law of Thermodynamics and Entropy

    48. ATMS 305 The Second Law of Thermodynamics and Entropy

    49. ATMS 305 The Second Law of Thermodynamics and Entropy The temperature-entropy and skew T-ln p diagrams

    50. ATMS 305 The Second Law of Thermodynamics and Entropy The temperature-entropy diagram Adiabats are perpendicular to isotherms Isobars are slightly curved Changes in temperature lapse rate in atmospheric soundings are readily discernible

    51. ATMS 305 The Second Law of Thermodynamics and Entropy The skew T-ln p diagram Ordinate is proportional to ln p Abscissa is proportional to (T + ln p) Isotherms are straight, parallel lines Adiabats are slightly curved lines Angle between isotherms and adiabats is nearly 90o

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