1. Efficiency of Heat Engines
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