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Unformatted text preview: Part VIII 2nd law Lecture 28 Carnot cycles The main results of classical thermodynamics were developed in the beginning of the 19th century, during the second industrial revolution. The second industrial revolution refers to the develop- ment of the steam-driven engine, as a power source (the first relied on water power). That is, the motivation for thermodynamics was to understand how to turn heat into work. Figure 1: Steam plant. Modern power plants share the same basic design (see Fig. 1): a heat source (a fire, or a nuclear reactor) that heats a working fluid (water, in a boiler), which expands to do work (in a turbine), and is cooled in a condenser where the waste heat is extracted by a heat sink (a river, or a cooling tower), whereupon the working fluid is sent back to the boiler. Key features of this design include: a heat source, and a heating step; an expansion step, in which work is done; a heat sink, and a cooling step; a cyclic process. Immediately the question arises, how e ffi ciently can we turn the heat from the heat source into useful mechanical work? From the experiments of Joule, which lead to the first law of thermodynamics 63 (energy conservation), we know that heat and work are both ways of changing the energy of a system. Work can be turned into heat with perfect e ffi ciency. What about the reverse process?ciency....
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This note was uploaded on 04/01/2008 for the course CHE 220 taught by Professor Prof.marannas during the Spring '08 term at Pennsylvania State University, University Park.
- Spring '08