tctc qhqh qcqc w thth. (a) - piston at room temp and atmospheric pressure p v a heat engine example
TRANSCRIPT
Tc
Qh
Qc
W
Th
(a) - piston atroom temp and
atmosphericpressure P
Va
Heat Engine Example
(a-b) - gasheated to keep
volumeconstant as
cart rolls ontopiston
P
Va
b
Heat Engine Example
(b-c) - gasheated toincrease
volume and liftthe cart
P
Va
b c
Heat Engine Example
(c-d) - gascooled to keep
volumeconstant atcart rolls off
pistonP
Va
b c
d
Heat Engine Example
(d-a) - gascooled to
reduce volumeback to initial
level
P
Va
b c
d
Heat Engine Example
Work done?
W, QH, QC, Efficiency, Power
1st Law
Energy is conserved
QWE int
2nd Law
Impossible to convert heat completely to work
i.e. no perfect heat engines
DO DREAMS MATTER?Scott Adams: "Losers have goals, winners have systems." "Success caused passion more than passion caused success."
vs.
Nathan Pacheco: Give dreams you attention - they aren't going to burn brighter in the future.
Carnot’s big ideaA reversible engine works as well backwards as forwards . . .
So no engine operating between two thermal reservoirs can have more efficiency than a reversible engine between the same reservoirs, and all reversible engines will have the same efficiency.
Carnot cycle1. Isothermal expansion2. Adiabatic expansion3. Isothermal compression4. Adiabatic compression
Carnot Efficiency
Carnot engine Most efficient engine possible:
h
c
h
c
T
T
Q
Q
1e
1Q
We
inHeat
Workefficiency
h
Perpetual motion
machines These machines violate either
– Conservation of Energy– 2nd Law of Thermodynamics
What is wrong with this picture?
My first million $
Generator
Battery
Recycling heat from exhaust
Otto Cycle
COP Refrigerators and Heat Pumps
Why gasoline?
“Gasoline stinks. It pollutes the atmosphere with carbon dioxide, and it is blamed for global warming and for nitrous oxides that cause smog. It finances totalitarian dictatorships and terrorists and drives us to war.”
– Richard Muller, Physics for Future Presidents
What about Batteries?
For the same weight : Gasoline has 100 times the usable
energy of the best rechargeable batteries