Transcript Chapter5-Thermal Ene..

Conservation of Energy
First Law of Thermodynamics
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True or False?
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Energy is conserved, only if no friction is
present.
Energy can be converted from one form to
another.
Work can be entirely converted to heat and
vice versa.
An ideal heat engine that works with no
friction is 100% efficient.
Construction of a time machine, although
possible, must wait a very long time.
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Thermal Energy
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What is heat?
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Heat and Temperature
Energy Conversion
Conservation of Energy (1st Law)
nd Law)
 Availability of Energy (2
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Efficiency
 Applications
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Nature of Heat
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Historical Perspective
Aristotle (Phlogiston)
 Lavoisier (caloric)
 William Thompson (motion)
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Heat and Temperature
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Temperature Conversion
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Temperature Conversion Formula
Following are the temperature conversion
equations for converting degrees centigrade
(C), fahrenheit (F), and kelvin (K).
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F = 1.8 C + 32
C = (F – 32) / 1.8
K = C + 273
(1)
(2)
(3)
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Modes of Heat Transfer
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Conduction
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Convection
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Transfer of heat from molecule to molecule
Transfer of heat by bulk motion
Natural vs. Forced Convection
Radiation
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Transfer of heat by electromagnetic waves.
Unlike conduction and convection, radiative heat transfer
requires no medium.
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Electromagnetic Spectrum
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First Law of Thermodynamics
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Historical Perspective
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Richard Meyer
Kelvin
Joule
Energy Conversion
First law efficiency
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Energy Conversion Devices
EXAMPLES OF DIFFERENT KINDS OF ENERGY CONVERSIONS
FROM/TO
MECHANICAL
THERMAL
CHEMICAL
MECHANICAL
Bicycle
Friction
Bomb
THERMAL
Heat Engines
Heat
exchanger
Pyrolysis
CHEMICAL
Rockets
Food
ELECTRICAL
Electric Motor
LIGHT
Galvanometer
ELECTRICAL
LIGHT
Wind
generator
Sparks
Thermo-couple
Luminescence
Metabolism
Fuel cell/
Battery
Candle
Resistor
Electrolysis
Transformer
Light bulb
Solar
collector
Photosynthesis
Solar cell
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Fluorescence
Availability of energy
Second Law of Thermodynamics
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Second Law of Thermodynamics
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Natural Direction and Arrow of Time
Entropy
Consequence of the Second law
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Heat cannot, by itself flow from a low to a high
temperature
Work can be completely converted to heat.
But heat cannot be completely converted to
work.
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Why work is more valuable than heat?
True or false: Which one is better? An electric
heater or a gas heater?
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True or false: Which one is better? A gas hot
water heater or a solar water heater?
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A very simple heat engine
Heat Engines
A heat engine is any device that uses heat
to perform work.
No real engine can have an efficiency
greater than that of a Carnot engine when
both engines work between the same two
temperatures.
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Claims, Lies and bigger lies
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An engine manufacturer makes
the following claims: The heat
input of the engine is 9 kW at
375 K. The heat output is 4 kW
at 225 K. Do you believe these
claims?
hactual = 1 - Qc/Qh = 1- 4/9 = 0.56
Hideal = 1 - Tc/Th = 1 - 225/375 = 0.4
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Living Organisms
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A living organism is an example of a heat engine which transforms
light energy into chemical energy
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Hurricane
A hurricane is an elegant
example of a natural Carnot
heat engine. It draws heat
from the ocean, releases some
of it to the atmosphere via
radiative cooling, and does
work during this process.
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True or false: Heat can never flow from a cold
reservoir to a hot one.
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True or false: A perfect engine produces no thermal
pollution.
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Basic Elements of a Heat Engine
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Thermal Devices
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Internal Combustion Engines
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Gasoline, diesel, and gas turbine
Refrigerator, Air Conditioners, and Heat
Pumps
Thermal Powerplants
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Thermal Power Plants
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Power Plant Operation (II)
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According to the second law of
thermodynamics, the higher the boiler
pressure (temperature), and the lower
the condenser temperature, the higher
is the efficiency of the power plant.
Wnet Wturbine  Wpump
η
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Qin
Q boiler
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How does it work?
Power Plants
 Gasoline Engines
 Diesels
 Jet Engines
 Refrigerators and A/C
 Heat Pumps
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How does a refrigerator work?
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If you leave your refrigerator door
open, the temperature in the room
will be...
Higher
Lower
The same
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How does a heat pump work?
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True or False?
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Energy is conserved, only if no friction is
present.
Energy can be converted from one form to
another.
Work can be entirely converted to work and
vice versa.
An ideal heat engine that works with no
friction is 100% efficient.
Construction of a time machine, although
possible, must wait a very long time.
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