629_Physics ProblemsTechnical Physics

629_Physics ProblemsTechnical Physics - 22 Heat Engines,...

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22 CHAPTER OUTLINE 22.1 Heat Engines and the Second Law of Thermodynamics 22.2 Heat Pumps and Refrigerators 22.3 Reversible and Irreversible Processes 22.4 The Carnot Engine 22.5 Gasoline and Diesel Engines 22.6 Entropy 22.7 Entropy Changes in Irreversible Processes Scale 22.8 Entropy on a Microscopic Heat Engines, Entropy, and the Second Law of Thermodynamics ANSWERS TO QUESTIONS Q22.1 First, the efficiency of the automobile engine cannot exceed the Carnot efficiency: it is limited by the temperature of burning fuel and the temperature of the environment into which the exhaust is dumped. Second, the engine block cannot be allowed to go over a certain temperature. Third, any practical engine has friction, incomplete burning of fuel, and limits set by timing and energy transfer by heat. Q22.2 It is easier to control the temperature of a hot reservoir. If it cools down, then heat can be added through some external means, like an exothermic reaction. If it gets too hot, then heat can be allowed to “escape” into the atmosphere. To maintain
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