1 / 17

170 likes | 171 Views

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

Download Presentation
## Announcements 9/21/11

**An Image/Link below is provided (as is) to download presentation**
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Content is provided to you AS IS for your information and personal use only.
Download presentation by click this link.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

**Announcements 9/21/11**• Prayer • Exam 1 starts a week from Saturday! • 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)**Video**• Adiabatic cotton burner • Mist from pressurized bottle**Special Processes: Review**• Constant volume (isovolumetric) • Constant pressure (isobaric) • Constant temperature (isothermal) • No heat added (adiabatic) • General process? • Eint = ? • Won gas = ? • Qadded = ? P B A V**P**State 1 V Last Special Case: Cyclical Processes • Eint = ? • Is it Wby gas or Won gas? • Qadded = ?**work**heat in (higher T) engine exhaust out (lower T) Engines: Energy Transformation • Qin = work by gas + Qout • Notation: Qh, Qc, Th, Tc, |W| • Qh = |W| + Qc**Heat Engine Example**a (a) - piston at room temp and atmospheric pressure P V**Heat Engine Example**(a-b) - gas heated to keep volume b constant as cart rolls onto piston P a V**Heat Engine Example**c (b-c) - gas heated to increase b volume and lift P the cart a V**Heat Engine Example**(c-d) - gas cooled to keep volume constant at cart rolls off piston d c b P a V**Heat Engine Example**c b (d-a) - gas P cooled to reduce volume d back to initial a level V**Efficiency**• How good is your engine? • Definition**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?**Reading Quiz (graded)**• What is the name we use for the cycle which models how a gas engine works? • Brayton cycle • Carnot cycle • Diesel cycle • Otto cycle • Tri cycle**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 Derived in book:**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? • They would get more efficient • They would get less efficient • The efficiency would not change**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**Worked problem: Class designed**• Make up a “three-legged cycle”. • What is the efficiency of this cycle? • Game plan: • Calculate Q for each leg • Calculate Qin, Qout, |W| • e = |W|/Qin • [Next class period: Test to make sure e < emax]

More Related