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Thermodynamics

Learn about the efficiency of heat engines and the second law of thermodynamics. Discover how net work and heat flow are related, and understand the concept of thermodynamic efficiency. Explore the laws of thermodynamics and their implications.

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Thermodynamics

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  1. Thermodynamics Efficiency of Heat Engines

  2. The Second Law of Thermodynamics • In an ideal cyclic process, internal energy is conserved • Net work = net heat flow • Wnet = Qnet = Qh – Qc • Qh is the heat absorbed by the heat engine or refrigerator or whatever • Qc is the heat given up to the surroundings

  3. The Second Law of Thermodynamics • Based on this, a heat engine could do more work on a hot day than it could a cold day and could always perform work as long as the engine’s temperature was less than the surrounding air temperature • This situation never happens

  4. The Second Law of Thermodynamics • The second law of thermodynamics – no cyclic process that converts heat entirely into work is possible • Some energy must always be transferred to the surroundings as heat

  5. Thermodynamic Efficiency • Efficiency is a rating of how well an engine works • What percentage of heat absorbed is converted to useful work • Efficiency = net work done by engine / energy added as heat • Efficiency = (energy added as heat – energy removed as heat) / energy added as heat • Efficiency = 1 – energy removed as heat / energy added as heat • Efficiency = 1 – temperature of cold reservoir / temperature of hot reservoir • eff = Wnet/Qh = (Qh-Qc)/Qh = 1-Qc/Qh = 1- (Tcold / Thot) • You can multiply by 100 to get a percentage

  6. Laws of Thermodynamics • 0th - You must play the game • 1st – You can’t win, you can only break even • 2nd – You can’t break even • 3rd – You can’t quit the game

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