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Conservation of Energy First Law of Thermodynamics

Conservation of Energy First Law of Thermodynamics. 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.

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Conservation of Energy First Law of Thermodynamics

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  1. Conservation of Energy First Law of Thermodynamics ENGR302I

  2. 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

  3. Thermal Energy • What is heat? • Heat and Temperature • Energy Conversion • Conservation of Energy (1st Law) • Availability of Energy (2nd Law) • Efficiency • Applications ENGR302I

  4. Nature of Heat • Historical Perspective • Aristotle (Phlogiston) • Lavoisier (caloric) • William Thompson (motion) • Heat and Temperature ENGR302I

  5. 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) ENGR302I

  6. 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. ENGR302I

  7. Electromagnetic Spectrum ENGR302I

  8. First Law of Thermodynamics • Historical Perspective • Richard Meyer • Kelvin • Joule • Energy Conversion • First law efficiency ENGR302I

  9. 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-couple Luminescence CHEMICAL Rockets Food Metabolism Fuel cell/ Battery Candle ELECTRICAL Electric Motor Resistor Electrolysis Transformer Light bulb LIGHT Galvanometer Solar collector Photosynthesis Solar cell Fluorescence Energy Conversion Devices ENGR302I

  10. Availability of energy Second Law of Thermodynamics ENGR302I

  11. 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. ENGR302I

  12. 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? ENGR302I

  13. A very simple heat engine

  14. 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. ENGR302I

  15. Claims, Lies and bigger lies • 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 ENGR302I

  16. Living Organisms • A living organism is an example of a heat engine which transforms light energy into chemical energy ENGR302I

  17. 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. ENGR302I

  18. True or false: Heat can never flow from a cold reservoir to a hot one. ENGR302I

  19. True or false: A perfect engine produces no thermal pollution. ENGR302I

  20. Basic Elements of a Heat Engine ENGR302I

  21. Thermal Devices • Internal Combustion Engines • Gasoline, diesel, and gas turbine • Refrigerator, Air Conditioners, and Heat Pumps • Thermal Powerplants ENGR302I

  22. Thermal Power Plants ENGR302I

  23. 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. ENGR302I

  24. How does it work? • Power Plants • Gasoline Engines • Diesels • Jet Engines • Refrigerators and A/C • Heat Pumps ENGR302I

  25. How does a refrigerator work? ENGR302I

  26. If you leave your refrigerator door open, the temperature in the room will be... • Higher • Lower • The same ENGR302I

  27. How does a heat pump work? ENGR302I

  28. 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. ENGR302I

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