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Announcements 3 rd exam Redo due Thursday, Dec. 4 th Presentations for Exam 3 (or 1 or 2) ???

Announcements 3 rd exam Redo due Thursday, Dec. 4 th Presentations for Exam 3 (or 1 or 2) ??? if ?? when?? how many?? Final exam, Wednesday, Dec. 10 th Extra problem solving sessions?? if ?? when?? how many??

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Announcements 3 rd exam Redo due Thursday, Dec. 4 th Presentations for Exam 3 (or 1 or 2) ???

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  1. Announcements • 3rd exam • Redo due Thursday, Dec. 4th • Presentations for Exam 3 (or 1 or 2) ??? • if ?? when?? how many?? • Final exam, Wednesday, Dec. 10th • Extra problem solving sessions?? • if ?? when?? how many?? • Physics colloquium Thursday, Dec. 4th at 4 PM • Professor Scott Wollenwebber, WFU School of Medicine -- "Positron Emission Tomography: From Basic Physics to Functional Images" • Today’s lecture – analysis of thermodynamic processes • Efficiency of a thermodynamic process • Carnot, Otto, Diesel processes • Notion of entropy PHY 113 -- Lecture 21

  2. Review of thermodynamic ideas “First law” of thermodynamics: DEint = Q - W For an ideal gas: PV = nRT Special cases: Isovolumetric (V=constant) W = 0 Isobaric (P=constant) Isothermal process (T=constant) DEint = 0 Adiabatic process (Q = 0) PHY 113 -- Lecture 21

  3. Extra credit: Show that the work done by an ideal gas which has an initial pressure Pi and initial volume Vi when it expands adiabatically to a volume Vf is given by: PHY 113 -- Lecture 21

  4. Pf B C P (1.013 x 105) Pa A D Pi Vi Vf Examples process by an ideal gas: Efficiency as an engine: e = Wnet/ Qinput PHY 113 -- Lecture 21

  5. Otto cycle: PHY 113 -- Lecture 21

  6. P d c b e PHY 113 -- Lecture 21

  7. P Otto cycle QAB=0 QCD=0 Example: r=5, g=1.4 e=0.475 PHY 113 -- Lecture 21

  8. Diesel cycle QAB=0 QCD=0 D A V Example: VD/VC=5, VA/VB=15, g=1.4 e=0.558 PHY 113 -- Lecture 21

  9. Stirling engine A P Th D Example: Th = 3Tc VB=VC=5VA=5VDg = 1.3 B Tc C PHY 113 -- Lecture 21

  10. Carnot process PHY 113 -- Lecture 21

  11. Carnot cycle PHY 113 -- Lecture 21

  12. Carnot cycle QBC=0 QDA=0 PHY 113 -- Lecture 21

  13. Examples Efficiency of a Carnot engine operating between the temperatures of Tc=0oC and Th=100oC:  For a Carnot engine, it is clear that we cannot achieve e=100%; not possible to completely transform heat into work. It is possible to show that the Carnot engine is the most efficient that one can construct between the two operating temperatures Tc and Th. PHY 113 -- Lecture 21

  14. Carnot cycle for cooling and heating “coefficient of performance” COPheating=|Qh/W|=Th/(Th-Tc) COPcooling=|Qc/W|=Tc/(Th-Tc) Example: Suppose that on a cold winter day, a heat pump has a compressor which brings outdoor air at Tc=-3oC into a room at Th=22oC. What is the COP? COP=295.15/25=11.8 PHY 113 -- Lecture 21

  15. More about Carnot cycle PHY 113 -- Lecture 21

  16. Carnot cycle shown in a T-S diagram: PHY 113 -- Lecture 21

  17. Other examples of entropy calculations: Ideal gas: Isovolumetric process: Isobaric process: Melting of solid having mass m and latent heat L at melting temperature TM: PHY 113 -- Lecture 21

  18. Pf B C P (1.013 x 105) Pa A D Pi Vi Vf Peer instruction question: Consider the “square cycle” shown below. What can you say about the entropy change in each cycle: • SABCDA= 0 • SABCDA> 0 • SABCDA< 0 PHY 113 -- Lecture 21

  19. PHY 113 -- Lecture 21

  20. PHY 113 -- Lecture 21

  21. PHY 113 -- Lecture 21

  22. PHY 113 -- Lecture 21

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