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ENGR302I
Conservation of EnergyFirst Law of Thermodynamics
ENGR302I
True or False? 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.
ENGR302I
Thermal Energy What is heat?
Heat and Temperature Energy Conversion
Conservation of Energy (1st Law) Availability of Energy (2nd Law)
Efficiency Applications
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Nature of Heat Historical Perspective
Aristotle (Phlogiston) Lavoisier (caloric) William Thompson (motion)
Heat and Temperature
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Temperature Conversion Temperature Conversion Formula
Following are the temperature conversion equations for converting degrees centigrade (C), fahrenheit (F), and kelvin (K).
F = 1.8 C + 32 (1) C = (F – 32) / 1.8 (2) K = C + 273 (3)
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Modes of Heat Transfer Conduction
Transfer of heat from molecule to molecule
Convection Transfer of heat by bulk motion Natural vs. Forced Convection
Radiation 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 Historical Perspective
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 ELECTRICAL
LIGHT
MECHANICAL Bicycle Friction Bomb Wind generator
Sparks
THERMAL Heat Engines
Heat exchanger
Pyrolysis Thermo-
coupleLuminescence CHEMICAL Rockets
Food
Metabolism
Fuel cell/ Battery
Candle
ELECTRICAL Electric Motor
Resistor Electrolysis
Transformer
Light bulb
LIGHT Galvanometer
Solar collector
Photosynthesis
Solar cell Fluorescence
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Availability of energy Second Law of Thermodynamics
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Second Law of Thermodynamics Natural Direction and Arrow of Time Entropy Consequence of the Second law
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?
True or false: Which one is better? A gas hot water heater or a solar water heater?
A very simple heat engine
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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.
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?
actual = 1 - Qc/Qh = 1- 4/9 = 0.56
ideal = 1 - Tc/Th = 1 - 225/375 = 0.4
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Living Organisms A living organism is an example of a heat engine which
transforms light energy into chemical energy
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HurricaneA 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 Internal Combustion Engines
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) 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.
boiler
pumpturbine
in
net
Q
WW
Q
Wη
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How does it work?Power PlantsGasoline EnginesDiesels Jet EnginesRefrigerators and A/CHeat 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?
ENGR302I
True or False? 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.