Transcript HeatEnergy

Heat Energy
• Read Textbook: Meteorology Today
– Chapter 2, Appendix G
• Homework Problems Chapter 2
– Questions for Review: 1, 3-5, 7, 8, 12-14, 17, 21
– Questions for Thought: 2, 7, 9-11
– Problems and Exercises: 1, 2, 4
Heat Energy
Temperature is our measurement of the average
kinetic energy found in the random motions and
vibrations of countless atoms and molecules.
Temperature is a way of quantifying the kinetic
energy of countless atoms and molecules.
Temperature is Energy.
Distribution of Speeds
Maxwell-Boltzman Velocity Distribution
Temperature and Kinetic Energy
T = a mwv2
a = 4.0 x 10-5 Ks2/m2
v2 = average molecular speed (KE)
mw = molecular weight
28.01
32.00
18.02
44.01
28.96
Molecule
N2
O2
H2O
CO2
Average Atmosphere
Temperature Conversions
CELCIUS
C = 5/9 (F-32)
FAHRENHEIT
F = (9/5 C) + 32
ABSOLUTE
or KELVIN
K = C + 273
Boiling Point of Water
CELCIUS
C = 5/9 (F-32)
C = 100
FAHRENHEIT
F = (9/5 C) + 32
ABSOLUTE
or KELVIN
K = C + 273
F = (9/5 100) + 32
= 180 + 32
= 212
K = 100 + 273
= 373
Freezing Point of Water
CELCIUS
C = 5/9 (F-32)
C = 5/9 (32-32)
= 0.0
FAHRENHEIT
F = (9/5 C) + 32
F = 32
ABSOLUTE
or KELVIN
K = C + 273
K = 0 + 273
= 273
Analog Temperature Conversion Plot
Celsius Fahrenheit
Kelvin
F
K
-20
-4
253 9/5*F +32 C + 273
0
32
273
20
68
293
40
104
313
60
140
333
80
176
353
100
212
373
Celsius to Fahrenheit Conversion
Celsius
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
-20
Series1
-30
420
400
380
360
340
320
300
280
260
240
220
200
180
160
140
120
100
80
60
40
20
0
-20
-40
-60
-80
-40
Fahrenheit
Celcius to Fahrenheit
Day Ground Temperature
Official
Temperature
is read at a
height of
1 meter
above the
ground, in
the shade,
and out of
the wind.
Night Ground Temperature
• The ground radiates away the daytime heat faster than the
air above it.
Air is a
very poor
conductor.
Air Turbulence
• Air motion causes mixing, removing stagnant boundary air
• Larger temperature gradients are possible without the wind
Radiation Shield
• Thick forest, Clouds can provide radiation shield
Thermal Insulation
• Thick Forest, Low Clouds can provide a thermal blanket
Temperature Data
Mean Daily Temperature:
average over 24 hours
Mean Annual Temperature:
average of 12 months
Average mean daily Temp.:
average of mean daily
temperatures over 30 years
Annual Temperature Range:
Difference between largest
monthly mean and smallest
monthly mean temperature.
Growing Days
• Number of days when the mean daily temperature is 1
degree above the base temperature for the particular crop.
Growing Degree
Day = Temp - Base
“Days to Maturity”
is inaccurate.
Cooling Degree Days
• Used during summer months to estimate energy and power
consumption needs for cooling indoor air. Base Temp = 65o
# = 1000’s
Heating Degree Days
• Used during winter months to estimate energy and power
consumption needs for heating indoor air. Base Temp = 65o
# = 1000’s
Controls of Temperature
• Solar Insolation (Chapter 3)
–
–
–
–
Date
Time
Latitude
Exposure (wind, humidity)
• Geographic
– Land
– Water
• Oceanic
– Currents
• Topography
– Elevation
Heat Index
• Appendix G
Humidity Formulas for Calculators
Heat Index Formula: RH=relative % humid., T = temp. (F)
Heat index or apparent temperature
= -42.379 + 2.04901523*T + 10.14333127*RH
- 0.22475541*T*RH - 6.83783x10-3*T2
- 5.481717x10-2*RH2 + 1.22874x10-3*T2*RH
+ 8.5282x10-4*T*RH2 - 1.99x10-6*T2*RH2
Calculations of relative humidity, dewpoint
temperature, and other quantities such as air density,
absolute humidity, and the height of cloud bases,
which are related to the moisture content of air.
http://www.usatoday.com/weather/whumcalc.htm
Wind Chill
• Wind Chill Equivalent Temperature
– If the air temperature is 10 degrees and the wind is 25 mph, the
wind chill equivalent temperature is -29 degrees.
Matter Phases
• In order of increasing Temperature (Energy):
–
–
–
–
–
CRYSTAL
SOLID
LIQUID
GAS
PLASMA
Occurring at the coldest temperatures
Occurring at the highest temperatures
Matter Phases
• In order of increasing Temperature (Energy):
–
–
–
–
–
CRYSTAL
SOLID
LIQUID
GAS
PLASMA
Occurring at the coldest temperatures
Occurring at the highest temperatures
• In order of decreasing Organization (Symmetry):
–
–
–
–
–
CRYSTAL
SOLID
LIQUID
GAS
PLASMA
Highly Ordered
Highly Disorganized
Water Crystals
Atomic and Molecular Structures Lead to Macroscopic Order
CHANGE OF STATE
Heat Energy must be absorbed by the solid to break the
highly ordered ice crystals. Heat Energy is released by a
liquid in order to crystallize.
Phase Transitions
State Changes
Energy Increased and Absorbed by Substance:
• SOLID to LIQUID
Melting
• LIQUID to GAS
Boiling
• SOLID to GAS
Sublimation
Energy Decreased and Released by Substance:
• GAS to SOLID
Deposition
• GAS to LIQUID
Condensation
• LIQUID to SOLID
Freezing
Phase Diagram
Latent Heat
Latent Heat of Fusion
Heat Energy required to
convert solid to liquid
Latent Heat of Evaporation
Heat Energy required to
convert liquid to gas.
Water Latent Heat Exchange
Condensation/Evaporation yield/require 6.75 times
more heat energy than Fusion/Melting.
Heat Units
• CALORIE: the amount of heat required to raise the
temperature of 1 kg of water by 1 degree Celsius.
• (1 Food calorie = 1,000 calories = 4.184 Joules)
Specific Heat
• Q = m c DT
Q = HEAT ENERGY
Human Perception
m = mass
DT = Temperature difference
c = specific heat responsible for the thermal
properties of the substance
(Joules/kg/oCelsius)
DT = Q/mc
Specific Heat
DT = Q/mc
For a given amount of heat energy, say 10,000 Joules,
what is the temperature change for 1 kg of water and
1 kg of sand?
Csand = 838 J/kgoC
Cwater = 4180 J/kgoC
DTsand = 10,000/1(838) = 11.9 oC
DTwater = 10,000/1(4180) = 2.4 oC
North versus South
Land masses dominate
the Northern Hemisphere
while oceans dominate
the Southern Hemisphere.
Land Versus Sea
Land masses in the
North cause more
temperature
variations than
in the South where
oceans keep
the temperature
even and
moderate.
Melting
DT = Q/mc
Amount of heat energy needed to bring a 25 g ice
block to a temperature of 50oC?
Starting Temp = 0oC
Ending Temp = 50oC
Q = heat needed to make transition from ice to water
+ heat needed to heat water from 0 to 50 oC
Q = mLf + mcDT
Melting Ice
Q = phase transition + mc DT
Q = heat needed to make transition from ice to water
+ heat needed to heat water from 0 to 50 oC
= 80 cal/g*(25 g)*(4.186 J/1000 Cal)
+ 25 g *4.186 J/goC *(50-0 oC)
= 8.37 J + 5230 J
= 5238.4 J
Freezing
This latent heat energy is released when water droplets
freeze.
Water vapor that condenses gives off latent heat as
well. Both processes help heat the atmosphere.
The opposite (melting or evaporation) causes heat
energy to be removed from the atmosphere.
CONDENSATION
• GAS to LIQUID (or Freezing, Liquid to Solid)
– ENERGY IS RELEASED, Gas has a higher internal
energy than the liquid state.
– A WARMING PROCESS
EVAPORATION
• LIQUID to GAS
– ENERGY IS REMOVED, Liquid has a lower internal
energy than the gaseous state.
– A COOLING PROCESS
Radiation
Energy transport via electromagnetic waves
Convection
Energy transport by mass motion
Conduction
Energy transport by vibrational translation
The jostling of atoms and
molecules in close proximity
in a solid, especially one with
high conductivity.
The Sun as a Blackbody Radiator (T=5800K)
Blackbody Radiation
Stefan-Boltzman Law
Energy Flux
E = sT4
Stefan-Boltzmann Constant
s = 5.6705 x 10-8 W/m2K4
Speed of Light
c=fl
f frequency and l wavelength
Wein’s Law
l = 3,000,000/T
Solar Constant
1370 Watts/m2
At the top of the
Earth’s Atmosphere
Energy Balance
Earth Albedo
• Reflection and Absorption of Incoming Solar Energy
Energy Budget
• Sunbeam (1370 W/m2) = 100%
– 30% reflected and scattered back out to space (411 W/m2)
• Earth’s surface (4%)
• Clouds (20%)
• Atmosphere (6%)
– 19% absorbed by Earth’s atmosphere (260.3 W/m2)
– 51% heats Earth’s surface (698.7 W/m2)
A Green House
Glass is transparent to short visible wavelengths (SW)
but opaque to long infrared (LW) wavelengths.
Atmosphere Absorption
Atmospheric
Absorption
Energy Transformations
• Radiant Solar Energy (1370 W/m2)
•
•
•
•
•
•
•
•
Heat Energy (Gas Kinetic Energy Increased)
Evaporation (Latent Heat)
Convection (Potential Energy Increased)
Condensation (Latent Heat Released)
Precipitation (Converting Potential to Kinetic Energy)
Erosion (Kinetic Energy causes Deformation)
Reservoirs (Potential Energy of a Dam)
Hydroelectric Power (Conversion of PE to KE to Electrical Energy)
• Evaporation (de ja vous)
Aurora
Magnetic Field
Magnetic Force
Force on a positive charge.
Moving Charges
Moving Charges in a Magnetic Field Experience a Force
Moving Charges can also create a Magnetic Field.
Oersted’s Experiment
A current carrying wire produces a magnetic field
Current Wire and Magnetic Field
Magnetic field direction depends upon
the direction of the current
Current Loop
What If the
Current is this…
Then the
Magnetic Field
is this...
I
B
Particles Spiraling
• Charged particles and a Magnetic Field (simulations)
http://www.phy.ntnu.edu.tw/java/emField/emField.html
http://www.lightlink.com/sergey/java/java/partmagn/index.html
Magnetosphere
• Solar Wind (charged particles) and Earth’s Magnetic Field
Auroral Probability Zones
• Number of Nights per Year Experiencing Northern Lights
Auroral Ionization Ring
http://www.pfrr.alaska.edu/~pfrr/AURORA/
Summary
• Temperature and Kinetic Energy
• Temperature Scales
– Kelvin
– Celsius
– Fahrenheit
• Physical Changes of State
– Latent Heat
– Specific Heat
• Energy Balance and Heating
– Radiation, Convection, Conduction
– Albedo
– Greenhouse Effect
• Aurora