Heat and Work: Part 2
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Transcript of Heat and Work: Part 2
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Heat and Work: Part 2
• Conservation of Energy
• Heat Engines
• Second Law of Thermodynamics
• Energy Efficiency
• OTEC
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Energy in the News• Possible solutions to Energy Problems
– 1) Smart Buildings and Machines– 2) Superconductive Cables– 3) Fewer Phantom Loads– 4) Distributed Generation
• A) Solar Cells
• B) Wind
• C) Diesel Generators
• D) Microturbines
• E) Fuel Cells
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Equilibrium of Heat Loss
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Heat Loss
• Hypothermia-what causes it? Basic physics
• Lakes-ice and summer warmth. Why retained?
• Space blankets-very thin-what do they do?
• Why cold when standing near a window in winter?
• Why warm near a fire?
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Heat Engines
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Two basic types of heat engines
• What are they?
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Vapor or Rankine Cycle
• Steam engines
• Heat pumps
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Gas Cycle
• Automobiles (Internal Combustion)
• Jet Engines (External Combustion)
• Where is the fuel burned?
• What does the force from burning move?
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Ocean Thermal Energy Conversion
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Practicalities of OTEC
• Maximum Efficiency (Carnot efficiency)
• =100% * ( Thigh-Tlow)/Thigh
• T in degrees Kelvin
• What is more efficient?
• Thermal engines with large or small temperature differences?
• When will it be 100% efficient?
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Second Law of Thermodynamics
• Entropy (Disorder) always increases Unless energy is added
• Examples:
• Kids room
• Spontaneous heat flow (Hot to Cold yes, never cold to hot)
• Waste Heat is always present
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Ideal Case
• A completely reversible process
• Do common heat engines use reversible processes, why or why not?
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Heat Pumps-How They Cool
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Why Pump from Ground Rather Than Air?
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Heat Pump in Winter
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Why Do Animals Burrow ?