Fall wk 3 – Mon.11.Oct.04
•
•
•
•
•
Welcome, roll, questions
Thermal physics and Energy Ch.3
break
continue Calculus Ch.1
Looking ahead
Energy Systems, EJZ
Discuss Ch.3,
Conventional conversion of energy
• Key points?
• Insights from team discussion?
• Questions?
- questions of fact: Can we find answer
in the text? What page?
- Outstanding questions of fact
- Outstanding significant questions
Energy conversion - outline
•
•
•
•
•
Scientific principles – App.A
Review of Thermal Physics
New: Power and Efficiency
Steam plant: closed cycle
Engine cycles: open
Laws of Thermodynamics
0. Thermal equilibrium
1. Energy can be neither created nor
destroyed.
Ex: Heat in = Work done + internal energy
2. Entropy increases: useful energy is lost
to heat
Heat = energy = work
Energy = force * distance
Joule = Newton * meter
J = kg m2/s2,
cal = 4.1868 J = 4 x 10-3 BTU
Horsepower = 1 hp = 550 ft * lb/s = 746 Watt
POWER = rate of doing work = Energy/time
Watts = Joules/sec
Efficiency = Energyin / Energyout = Powerin / Powerout
Q: What is a kilowatt-hour? A measure of:
A. Energy
B. Power
C. Efficiency
Thermal energy  heat engine
Steam power plant
• closed cycle, external combustion
• burn fossil fuel  heat water  steam  move
turbines  electricity
Gas and diesel engines
• open cycle, internal combustion
• compress  heat  ignite  expand  motion
Steam plant
burn fuel  heat water  steam  move turbines  electricity
Increase efficiency by
decreasing losses
Generator: motion  electricity
Electric Power = Voltage * Current: P = VI
Ohm’s law: Voltage = Current * Resistance: V = IR
Higher voltage transmission: lower ohmic losses
Engine cycles
compress  heat  ignite  expand  motion
Gas engines are usually less efficient than diesel engines
Work done by a gas (CT 3, 64, green)
Work done = pressure * volume = area under curve (clockwise)
Heat added = work done + change in internal energy of gas
How to improve engine performance?
• thermal efficiency is limited, since waste heat is
exhausted
• compression ratio – diminishing returns, and higher
temps  preignition
• * lower weight  better performance: a = F/m
• aerodynamics – small effect
• power train designs – gradual improvements
• * driving habits, mass transit
Calculus - outline
•
•
Modified Calc HW
Practice with logarithmic functions
(Pre)Calculus question for seminar:
If global energy use increases by 2.5% per
year, how long will it take for global
demand to double?
a. First, guess.
b. What is the percent increase if it doubles?
c. Hint: D = D0 at
Calc 1 HW 2
Homework due this Thus: Calc 1 HW 2 without
Ch.1.5
1.4 # 1, 2, 9, 11, 14, 18, 26, 35
1.6 # 2, 4, 14, 28
Next Thus: Calc 1 HW 3
1.5 # 1, 10, 14, 16, 20, 29, 31, 34, 36
1.6 # 8, 18, 23
Phys 18 HW 1
Thermal (and basic) physics problems due this Thus:
Ch.1 #5, 7, 16, 18, 24, 26, 29
Ch.18 #4, 5, (24), 26, 28, 35, (73, 85)
Problems in (parentheses) are not available on eGrade.
Hand them in separately?
I will post solutions after class Thus.
Phys 18 HW 2 due next Thus:
Ch.18 # (27), 29, 32, 33, (94)
Looking ahead
• Seminar in Sem II C2109 tonight
• Please put your team’s best Q on the board
before 5:00 so we can start on time
• Tomorrow:
– Debate: Coal vs Fission
– visitors will discuss sustainability and solar
panels on Tuesday and Wednesday
• Later:
- TA available here Wed 1-3, QRC Fri 10-12
- Next Mon. CE Fair – we’ll set up telescope
Heat of transformation ConcepTests
80
Work done by gas ConcepTests
Steam plant cycle
Diesel engine cycle
Hydroplant