Lecture 36 - Lecture 36 pls-36.1 Heat Engines and the 2nd...

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Lecture 36 pls-36.1 Heat Engines and the 2 nd Law of Thermodynamics Media: 1. Steam engine 2. Convection demonstration 3. Fan with two cups of liquid 4. Figs. 1 – 5, class notes 5 1. Heat Engines A Heat Engine converts microscopic energy into net , sustained , macroscopic work. Examples/Demos: internal combustion engine Biological entities Steam engine Convection demonstration Fan with two cups of liquid Microscopic Energy Æ Macroscopic Work What does 1 st Law have to say about this? Consider an isothermal process, 0 = U , associated with some thermodynamic system. Then W Q U = Æ Q W = . So it looks like we could convert Q into W with 100% efficiency. But this cannot be done in a sustainable manner. To do it in a sustainable manner, some of the microscopic energy must be thrown away. This is the essence of the second 2 nd Law of thermodynamics.
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Lecture 36 pls-36.2 2 nd Law : Consider a thermodynamic system. For sustained work by this system (on the outside world) some of the heat flow in (
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Lecture 36 - Lecture 36 pls-36.1 Heat Engines and the 2nd...

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