Transcript energy use and sources - Fort Thomas Independent Schools

HEAT ENGINES
HEAT ENGINE
A
heat engine is any device that changes
thermal energy into mechanical
energy so work can be done.
 Mechanical work can be done only if heat
flows from a high-temperature to lowtemperature region.
HEAT FLOW IN A
High
Temp
Heat
in
Work
Heat
out
Lower
Temp
HEAT ENGINE (STEAM)
THERMAL ENERGY IN : MECHANICAL ENERGY OUT
The process of an internal combustion
engine resembles that of a heat engine.
http://www.planemath.com/activities/pmenterprises/propulsi
on/propulsion3.html
HEAT ENGINES

Only some of the heat transferred from the hightemperature region can be transformed into mechanical
energy (work). The remainder of the thermal energy is
exhausted as waste heat.
Phases of Matter

Solid

Liquid

Definite volume and shape


Definite volume
Undefined shape

Plasma

Undefined volume and shape
Electrically charged gas—High
temp!
Neon, lightning, stars, auroras,
fluorescent bulbs

Gas

Undefined volume and
shape

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Melting and Evaporation Require
Input of Thermal Energy

Melting (requires heat of fusion)


Heat of fusion is released when liquids freeze
Evaporation (requires heat of vaporization)

Heat of vaporization is released when gases condense
Evaporation vs. Condensation

Evaporation is a cooling
process

Condensation is a
warming process

Evaporation causes the
temperature of the
liquid to decrease
(removes thermal
energy from
surroundings)

Condensation causes
the temperature of the
surroundings to
increase (adds thermal
energy to the
surroundings)
23.8 Energy and Changes of Phase
If you heat a solid sufficiently, it will melt and become a liquid.
If you heat the liquid, it will vaporize and become a gas.
The change in the internal energy of a substance causes the
change of phase.
23.1 Evaporation
The cloth covering on the
sides of the canteen
promotes cooling when it is
wet. As the faster-moving
water molecules leave the
cloth, the temperature of the
cloth decreases.
Starter Question #2
How does a thermometer work?
The kinetic theory be used to explain expansion and
contraction of materials when the temperature of
the material changes.
As the temperature rises, heat is transferred from the
surroundings to the liquid inside the thermometer
and the molecules that compose the liquid vibrate
faster. This causes the liquid to expand and rise.
As the temperature falls, heat is transferred away from
the liquid inside to the surroundings and the
molecules that compose this liquid slow down.
This causes the liquid to contract.

The liquid in the thermometer stops rising or falling
when thermal equilibrium is reached (no more heat
flow!)
Air temperature = Liquid temperature
Winter Vs. Summer Heat Flow
In winter
-Heat loss from inside
(warmer) to outside
(colder)
-Heating system must
operate to transfer
thermal energy from
fuel to fluid to room
to keep house warm

In summer
-Heat gain from outside
(warmer) to inside
(cooler)
- Cooling system must
operate to transfer
incoming heat entering
the house back to the
outside

21.7 The High Specific Heat Capacity of Water
Water has a high specific heat and is transparent, so it takes
more energy to heat up than land does.
Moderating Effect of Water on Climate
Water has a high specific heat capacity. This
means…
 It takes a large amount of heat to raise its
temperature
 It absorbs a large amount of heat
 It stores a large amount of heat
 It has to give up a large amount of heat in
order to cool down
 It takes a long time for water to cool down

Moderating Effect of Water on Climate


During the summer, surrounding air is cooled by the
water and keeps the coast cooler than the
intercontinental locations.
During the winter, the surrounding air is warmed by
the water and keeps the coast warmer than the
intercontinental locations.
SAN FRANCISCO, CA
21.7 The High Specific Heat Capacity of Water
Water stores and hold heat well because of its high specific
heat. This affects global climate.
Gulf Stream brings warm water
northeast from the Caribbean.
Thermal Front
The Gulf Stream (warm
water from equator)
meets
The Labrador Current
(cold water from polar
region)
Labrador
Current
Gulf
Stream
21.7 The High Specific Heat Capacity of Water
Climate of America
On the west coast, air moves from the Pacific Ocean to the
land.
• In winter, the water warms the air that moves over it and
warms the western coastal regions of North America.
• In summer, the water cools the air and the western
coastal regions are cooled.
The central interior of a large continent usually
experiences extremes of temperature.
Land, with a lower specific heat capacity, gets hot
in summer but cools rapidly in winter.
21.7 The High Specific Heat Capacity of Water
Climate of Europe
Look at a world globe and notice the high
latitude of Europe.
Both Europe and Canada get about the
same amount of the sun’s energy per
square kilometer.
Marine Climate
Continental Climate
Cork
Edmonton
http://www.sampleireland.com/weather-in-ireland-year-round.html
Marine Climate
Continental Climate
Cork
Edmonton
Same insolation
angle, different
climate due to
proximity to water
and the warming
effect from the
Gulf Stream
http://www.sampleireland.com/weather-in-ireland-year-round.html
The Gulf Stream brings warm winters to Ireland and the prevailing winds off the
Atlantic carry with them rain. It means grass can grow almost all year round —
creating the lush sweeping pastures of the Emerald Isle. Today they make up 93
percent of all farmland. No other country in Europe has quite as much grass as
Ireland.
Comparing Climate Data
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Cork, Ireland and Edmonton, Alberta, in Canada are close to the same
latitude
 Cork is 51°47'N
 Edmonton is 53° 34' N
Find the following for Cork, Ireland
 Average daily high and low temperatures for Jan.
____ ____
 Average daily high and low temperatures for July
____ ____
 Temp. variation for winter to summer (hi/low)
____ ____
 Average Precipitation for January and July
Find the following for Edmonton, Alberta (you will have to convert
Celsius to Fahrenheit and mm to inches)
 Average daily high and low temperatures for Jan.
____ ____
 Average daily high and low temperatures for July
____ ____
 Temp. variation for winter to summer (hi/low)
____ ____
 Average Precipitation for January and July
____ ____
Why are the climates for these two cities so different? (Read Ch 21.7, pg.
415-416 )
Comparing Climate Data

Cork, Ireland and Edmonton, Alberta, in Canada are close to the same latitude

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Compare the climates for each using the graphs provided. You will have to convert
Celsius to Fahrenheit and mm to inches to make comparison!
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Cork is 51°47'N
Edmonton is 53° 34' N)
Coldest month and average day and night temperatures (data is already averaged!)
Warmest month and average day and night temperatures (data is already averaged)
Average summer high and low temperatures (you average the temperature over three summer
months)
Average winter high and low and temperatures (you average the temperature over three winter
months)
Temperature Mean for day and night (average 12 day and 12 night temperatures)
Month with greatest precipitation and least precipitation
Precipitation variation (amount of change from highest to lowest)—difference between highest
and lowest
Temperature variation (amount of change from highest to lowest average day and night
temperatures)
Why are the climates for these two cities different? (read attachment on-line)
Reason for the Seasons
2
Changing Angle of Sunlight
• The hemisphere tilted toward the Sun receives sunlight at
higher angles than the hemisphere tilted away from the Sun.
• Higher insolation angle means greater intensity of radiant
energy (the sun shines more directly on a smaller area).
Summer in Northern Hemisphere
Identify the Seasons and the Equinox or Solstice, and comment about the number
of daylight vs. night hours
Season _________
_________
Equinox or Solstice
Season _________
Season _________
Equinox or Solstice
Equinox or Solstice
Season ________
Equinox or Solstice
Identify the Seasons and the Equinox or Solstice
Equal day and night—12hr and 12 hr
Season _________
spring
Equinox or Solstice
Less night
hours, more
daylight
hours
Less daylight
hours, more
night hours
winter
Season _________
summer
Season _________
Equinox or Solstice
Equinox or Solstice
fall
Season _________
Equinox or Solstice
FUNCTION OF A REFRIGERATOR
Remove
unwanted
Thermal Energy
from inside
By evaporation
Deposit
unwanted
Thermal Energy
on the outside
By condensation
HOW DO AIR CONDITIONERS
AND REFRIGERATORS WORK?

Evaporation of refrigerant removes thermal energy
from inside.


Evaporation occurs when liquid refrigerant is allowed to
expand (pressure release—lowers vaporization point—heat
drawn from food causes evaporation)
Condensation of refrigerant releases thermal energy
to the outside

Work must be done by the compressor to compress the
refrigerant gas so that the thermal energy drawn from food
is released outside when the gas is forced to condense
under pressure)

22.
How do natural systems tend to proceed?
24.7 Entropy
According to the second law of thermodynamics, in
the long run, the entropy of a system always increases
for natural processes.
24.6 Order Tends to Disorder
Natural systems tend to proceed toward
a state of greater disorder.
The universe trends from a higher state
to a lower state of organization.
Examples:
Air flows from high to low pressure
Heat flows from hot to cold
24.7 Entropy
Entropy is the measure of the amount of disorder
in a system.
Disorder increases; entropy increases.
24.7 Entropy
This run-down house demonstrates entropy. Without continual
maintenance, the house will eventually fall apart.