Heat and Work: Part 1

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Heat and Work Part 1

• Heat
• Work
• First Law of Thermodynamics
• Temperature and Heat
• How Heat is Transferred

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Energy in the News

• Special Section of Wall Street Journal
• Lessons Learned from California
• Electricity is unique-delivery simultaneous
• Utilities-long term contracts needed
• Generating capacity-need enough, not too much
• Consumers-no insulation from price changes
• Regulators-must stay current

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US Household Energy Use
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First Law of Thermodynamics

• Total Energy (E) Sum of All Energy
• Types of Energy?
• Two ways to change energy content (if no mass
  involved)
• 1) Do work
• 2) Add heat

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Heat and Work
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First Law Summarized

• Work done Heat Added
• Change in Energy of the System
• Sum Up Changes (Delta)

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Bicycle Pump
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Movement of a Piston
Piston moves up and gas under piston is
decompressed. Result is that the gas gets cooler
(the gas loses energy). Energy is transferred
from the gas to the outside. In a car this
energy moves the crankshaft and then the wheels
of the car.
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Temperature Scales

• What is temperature?
• Fahrenheit Scale
• Centigrade Scale
• Kelvin Scale
• Equal at what temperature?
• Historical Basis

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Relationship of Temperature and Heat

• Q MCDelta T
• Qheat
• Cspecific heat
• Delta Tchange in temperature
• Mmass

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Reference Points for Temperature
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Specific Heats
What substances Are the best insulation? Why? Wh
at substances conduct heat well? Why?
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Thermal Energy (Thermal Mass)
Passive Solar Houses How Applicable?
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Energy in Water Phase Change
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Water Phase Change-Another Picture
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Heat Transfer

• What are the three methods of heat transfer?

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Conduction
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Heat Flow Equation

• Q/t kA (T2-T1)/delta

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Convection

• Convection currents in a pan on a hot stove.

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Mechanically Aided Convection
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Passive Convective System

• What do you think they mean by passive and active
  solar heating?

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Insulation How it works
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Light The Spectrum

Visible Light small portion of
electromagnetic spectrum Other
parts infrared ultraviolet radio Where is
infrared/ ultraviolet on this picture?
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Emission or Radiation of Heat
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Spectrum-Detailed Divisions
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Earth and Sun Radiate Differently
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Emissivity of Windows
Low e film on windows-how does it work?
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All Three Methods at Once
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Energy Savings from ThermostatChanges
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Solar Heater Active or Passive?
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Efficient Windows How do they work?
Why argon gas between panes? Why have triple
panes?