1. Mon. Apr. 20 – Physics Lecture #39 Heat Engines and the Second Law of Thermodynamics 1. Lab 32: It’s Getting Hot In Here – Heat Engine Demos 2. Energy, Work, Heat, and the First Law of Thermodynamics 3. Cyclic Processes, Heat Engines, Heat Pumps, Refridgerators 4. Efficiency, Entropy, and the Second Law of Thermodynamics

2. Internal Combustion Engine An internal combustion engine can be modeled using the following four step, cyclic process. Process 1: Fill the piston with an air/gas mixture, and compress it adiabatically to a lower volume. Process 2: Ignite the air/gas mixture. The temperature rapidly increases without the volume changing very much (due to the rapidity of the process). Process 3: The high pressure gas pushes the piston back to its starting volume during the adiabatic power stroke. Process 4: The gas cools down, at constant volume, basically by expelling the hot exhaust and filling the piston with a cool air/gas mixture. Process 1: adiabatic compression 1 Process 2: T increases, V constant 2 Process 3: adiabatic expansion 3 Process 4: T decreases, V constant 4 V P QhQh QcQc

3. Heat Engine High temperature reservoir Engine (cyclic) Low temperature reservoir |Energy In| = |Energy Out| Efficiency: Heat removed from high temperature reservoir is added to engine. Heat removed from engine is added to low temperature reservoir. Engine turns some heat into work; some heat removed from engine.

4. Heat Engine High temperature reservoir Engine (cyclic) Low temperature reservoir Heat Pump/Refrigerator High temperature reservoir Fridge (cyclic) Low temperature reservoir

5. A power plant produces 100 MJ of electricity. The plant runs from a nuclear fission reactor, which boils water and feeds 400 MJ of energy into a turbine generator. How much heat is dumped into the local river during this process? 1.0 MJ 2.100 MJ 3.300 MJ 4.400 MJ 5.500 MJ 6.Not enough info What is the efficiency of this engine?

6. Let’s say we tried to make an engine that would take 300 J of energy from a 600 K hot reservoir and turn it all into work. What is the total entropy change of the universe (the heat reservoir + the engine)? What is the maximum amount of the 300 J that could be turned into work?

8. c) If this cycle were used as the engine part of a heat engine, determine the efficiency of the engine. d) Verify the two entries provided in the table.