Power use per
person per day,
by Country
(2007)
Why do we use the unit of the “Joule”?
Why do we use the unit of the “Joule”?
The physicist James Joule (1843) discovered that the
amount of energy needed to raise the temperature of
water was the same whether it was work done on the
water or heat added.
Joule’s mechanical
heating apparatus
(1845)
First Law of
Thermodynamics:
Heat = Work
W = ΔE = ΔTE
So, how much heat do you need to add to raise the
temperature of 1 gram of something 1°C?
It depends on the substance!!!
Q = mcΔT
Heat added = (mass)(specific heat)(change in T)
What are some consequences of this for climate and
climate change?
THIS is how the “calorie” and
“Btu” were defined!
1 calorie = energy required to
raise 1 gram of water 1°C
1 Btu (British thermal unit) =
energy required to raise 1 pound
of water 1°F
THIS is how the “calorie” and
“Btu” were defined!
1 calorie = energy required to
raise 1 gram of water 1°C
1 Btu (British thermal unit) =
energy required to raise 1 pound
of water 1°F
It takes 4.19 kJ to raise 1 kg of
water 1°C
It takes a LOT of energy to get water to change its phase
(to get ice to melt, and to get liquid water to boil)!
It takes a LOT of energy to get water to change its phase
(to get ice to melt, and to get liquid water to boil)!
Heat of Fusion: It takes 335 kJ to turn 0°C ice into 0°C
water
Heat of Vaporization: It takes 2260 kJ to turn 100°C
water into 0°C steam
How much energy does it take to turn 1 kg of 0°C ice
into 100°C steam?
How much energy does it take to turn 1 kg of 0°C ice
into 100°C steam?
E = 335kJ + (4.19 kJ/°C)(100°C) + 2260 kJ
= 335 kJ + 419 kJ + 2260 kJ = 3014 kJ
HEAT flow by three mechanisms:
Conduction
Convection
Radiation
Fig. 4-7, p. 106
CONDUCTION:
k = thermal conductivity
CONDUCTION:
R = δ/k = “R value”
Qc = A x (T2 – T1)
t
R
Table 5-2a, p. 134
Table 5-2b, p. 134
Equivalent thicknesses needed to provide an R value of
R = 22 (ft2hr°F/Btu)
CONVECTION:
RADIATION (Electromagnetic):
RADIATION (Electromagnetic):
RADIATION (Electromagnetic):
Many energy-related machines
are examples of a “Heat Engine”
 Transforms Heat into Work
Ex/ Steam engines, combustion
engine, heat pump (refrigerator
or air conditioner)
Efficiency = Work out x 100%
Energy in
Efficiency = Work out x 100%
Energy in
= (Heat in – Heat out) x 100%
Heat in
Efficiency = Work out x 100%
Energy in
= (Heat in – Heat out) x 100%
Heat in
= (TH – TC) x 100%
TH
Efficiency = (TH – TC) x 100%
TH
The HOTTER an engine runs, the
more efficient it is.
Efficiency = (TH – TC) x 100%
TH
The HOTTER an engine runs, the
more efficient it is.
Ex/ If TH = 400K and TC = 300K
then Max possible efficiency =
(400K – 300K)/400K = 25%
Efficiency = (TH – TC) x 100%
TH
The HOTTER an engine runs, the
more efficient it is.
Ex/ If TH = 400K and TC = 300K
then Max possible efficiency =
(400K – 300K)/400K = 25%
Ex/ If TH = 1000K and TC = 300K
then Max possible efficiency =
(1000K – 300K)/1000K = 70%
Efficiency = (TH – TC) x 100%
TH
The HOTTER an engine runs, the
more efficient it is.
Ex/ If TH = 400K and TC = 300K
then Max possible efficiency =
(400K – 300K)/400K = 25%
Ex/ If TH = 1000K and TC = 300K
then Max possible efficiency =
(1000K – 300K)/1000K = 70%
It can never be 100%!
Second Law of Thermodynamics
1) Heat can flow spontaneously (by itself) only from a hot
source to a cold sink.
Second Law of Thermodynamics:
1) Heat can flow spontaneously (by itself) only from a hot
source to a cold sink.
2) No heat engine can be 100% efficient; some heat
always has to be discharged to a sink at a lower
temperature
Which of these will happen?
Second Law of Thermodynamics:
 In ANY system, the result of an interaction will be an
INCREASE in disorder (Entropy)
 Time has a direction! (toward disorder)
Which of these will happen?
How does an air conditioner work?
How does an air conditioner work?
What happens to a gas when you compress it?
A heat pump (air conditioner, refrigerator) uses the trick
that gases become hot when compressed, cold when
expanded.
A heat pump (air conditioner, refrigerator) uses the trick
that gases become hot when compressed, cold when
expanded.
1. HOT
A heat pump (air conditioner, refrigerator) uses the trick
that gases become hot when compressed, cold when
expanded.
2. Cools off
1. HOT
A heat pump (air conditioner, refrigerator) uses the trick
that gases become hot when compressed, cold when
expanded.
2. Cools off
1. HOT
3. Ambient
A heat pump (air conditioner, refrigerator) uses the trick
that gases become hot when compressed, cold when
expanded.
2. Cools off
1. HOT
3. Ambient
4. COLD
A heat pump (air conditioner, refrigerator) uses the trick
that gases become hot when compressed, cold when
expanded.
2. Cools off
1. HOT
5. Warms up
3. Ambient
4. COLD
A heat pump (air conditioner, refrigerator) uses the trick
that gases become hot when compressed, cold when
expanded.
6. Ambient
2. Cools off
1. HOT
5. Warms up
3. Ambient
4. COLD
You can also do
this by changing
the phase – from
liquid to gas and
back again.
You can also do
this by changing
the phase – from
liquid to gas and
back again.
The gas GIVES OFF
heat when you
compress it into a
liquid
You can also do
this by changing
the phase – from
liquid to gas and
back again.
The gas GIVES OFF
heat when you
compress it into a
liquid
The gas
ABSORBS heat
when you let it
expand back
into a gas
What are three
things about the
world’s energy
future that most
concern you?
What are three
things about the
world’s energy
future that make
you optimistic?
1)
1)
2)
2)
3)
3)