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Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. Doodle survey about exam review times, vote for times before Friday If you emailed me about Mathematica issues on HW 7 and still need to turn it in, do so by Friday Regarding showing your work for the TA: (Foxtrot)
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Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Dec 19, 2015

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Page 1: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday!

a. Doodle survey about exam review times, vote for times before Friday

If you emailed me about Mathematica issues on HW 7 and still need to turn it in, do so by Friday

Regarding showing your work for the TA: (Foxtrot)

Page 2: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Video

Adiabatic cotton burner Mist from pressurized bottle

Page 3: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Special Processes: Review

Constant volume (isovolumetric) Constant pressure (isobaric) Constant temperature (isothermal) No heat added (adiabatic) General process?

a. Eint = ?

b. Won gas = ?

c. Qadded = ?

A

B

P

V

Page 4: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Last Special Case: Cyclical Processes

Eint = ?

Is it Wby gas or Won gas?

Qadded = ?

P

V

State 1

Page 5: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Engines: Energy Transformation

Qin = work by gas + Qout

Notation: Qh, Qc, Th, Tc, |W|

Qh = |W| + Qc

engineheat in(higher T)

work

exhaust out (lower T)

Page 6: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

(a) - piston atroom temp and

atmosphericpressure P

Va

Heat Engine Example

Page 7: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

(a-b) - gasheated to keep

volumeconstant as

cart rolls ontopiston P

Va

b

Heat Engine Example

Page 8: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

(b-c) - gasheated toincrease

volume and liftthe cart

P

Va

b c

Heat Engine Example

Page 9: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

(c-d) - gascooled to keep

volumeconstant atcart rolls off

piston

P

Va

b c

d

Heat Engine Example

Page 10: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

(d-a) - gascooled to

reduce volumeback to initial

level

P

Va

b c

d

Heat Engine Example

Page 11: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Efficiency How good is your engine? Definition

Page 12: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Worked Problem A car engine produces 5000 W of power,

at 20 cycles/second. Its efficiency is 20%. What are |Wnet|, Qh, and Qc per cycle?

What do those quantities represent?

Page 13: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Reading Quiz (graded)

What is the name we use for the cycle which models how a gas engine works?

a. Brayton cycle b. Carnot cyclec. Diesel cycled. Otto cyclee. Tri cycle

Page 14: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Otto Cycle: Gas Engines (Starting at 2)

Piston is com-pressed 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)

→ We pretend heat is added without changing gas

Image credit: http://www.grc.nasa.gov/WWW/K-12/airplane/otto.html

“Compression ratio” r = Vmax/Vmin

1

11Ottoer Derived in book:

Page 15: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Thought Question

If I replaced all of the nitrogen (N2) in the air with carbon dioxide (CO2), what do you think would happen to the efficiency of car engines?

a. They would get more efficientb. They would get less efficientc. The efficiency would not change

1

11Ottoer

Page 16: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

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

Page 17: Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed.

Worked problem: Class designed

Make up a “three-legged cycle”. What is the efficiency of this cycle? Game plan:

a. Calculate Q for each legb. Calculate Qin, Qout, |W|

c. e = |W|/Qin

d. [Next class period: Test to make sure e < emax]