1. Announcements 9/22/10 HW solutions 1-8 posted… but running out of space This is what I see when I grade clicker quizzes: Quiz 6 No student assigned to transmitter 1B0E1C09 No student assigned to transmitter 1FC8F72 No student assigned to transmitter 8FF4FB8 No student assigned to transmitter 13149F98 No student assigned to transmitter 7586837 No student assigned to transmitter 1B5B3D7D No student assigned to transmitter 141E909A No student assigned to transmitter 13CA2FF6 Question 1 Average score: 1.00/ 1 ( 38 students) Question 2 Average score: 1.76/ 2 ( 41 students) Question 3 Average score: 1.00/ 1 ( 41 students) Question 4 Average score: 1.49/ 2 ( 41 students) Question 5 Average score: 1.00/ 1 ( 40 students) Question 6 Average score: 1.00/ 1 ( 41 students) Question 7 Average score: 1.00/ 1 ( 41 students) Question 8 Average score: 1.00/ 1 ( 40 students) Average score on quiz: 9.24/10 Deadline to get your clicker registered: start of exam (next week)

2. Quick writing When I expand a gas from one volume to another, the final pressure will be greater if it is expanded isothermally than if it is expanded adiabatically. Explain why without using equations.

3. Special Processes: Review Constant volume Constant pressure Constant temperature No heat added General process? a. a.  E int = ? b. b.W on gas = ? c. c.Q added = ?

4. Last Special Case: Cyclical Processes  E int = ? net W by gas or W on gas ? |W| = ? Q added = ? P V State 1

5. Engines: Energy Transformation Q in = work by gas + Q out Notation: Q h, Q c, T h, T c, |W| Q h = |W| + Q c engine heat work exhaust

6. (a) - piston at room temp and atmospheric pressure P V a Heat Engine Example

7. (a-b) - gas heated to keep volume constant as cart rolls onto piston P V a b Heat Engine Example

8. (b-c) - gas heated to increase volume and lift the cart P V a b c Heat Engine Example

9. (c-d) - gas cooled to keep volume constant at cart rolls off piston P V a b c d Heat Engine Example

10. (d-a) - gas cooled to reduce volume back to initial level P V a b c d Heat Engine Example

11. Efficiency How good is your engine? Definition

12. Worked Problem A car engine produces power of 5000 W, at 20 cycles/second. Its efficiency is 20%. What are |W|, Q h, and Q c per cycle? What do those quantities represent?

13. Reading Quiz (graded) What is the name we use for the cycle which models how a gas engine works? a. a.Carnot cycle b. b.Brayton cycle c. c.Diesel cycle d. d.Otto cycle e. e.Tri cycle

14. Otto Cycle: Gas Engines (Starting at 2) Piston is compressed quickly Heat is then added quickly by igniting fuel (const volume) Piston then expands quickly Heat is then expelled quickly (by getting rid of old air) → In our approxi- mation we pretend like same air is reused Image credit: http://www.grc.nasa.gov/WWW/K-12/airplane/otto.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/otto.html “Compression ratio” r = V max /V min Derived in book:

15. Thought Question If I replaced all of the nitrogen (N 2 ) in the air with carbon dioxide (CO 2 ), what do you think would happen to the efficiency of car engines? a. a.They would get more efficient b. b.They would get less efficient c. c.The efficiency would not change

16. Diesel Cycle: Diesel Engines What’s the main difference between gas and diesel engines? Change to our PV-diagram model Diesel cycle details… done in HW problem

17. Worked problem: Class designed Make up a “three-legged cycle”. What is the efficiency of this cycle? Game plan: a. a.Calculate Q for each leg b. b.Calculate Q in, Q out, |W| c. c.e = |W|/Q in d. d.Test to make sure e < e max