engr302i conservation of energy first law of thermodynamics

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Conservation of EnergyFirst Law of Thermodynamics

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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.

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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?

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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.