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Engines and Refrigerators

The laws of energy conservation and entropy increase put limits on the efficiency of any heat engine and any refrigeration device working over a given temperature range. The limits are independent of the details of how these machines operate, so this chapter first explains them by considering only energy and entropy flows. The detailed mechanisms are still interesting, however, so the chapter ends with descriptions of a variety of engine and refrigeration mechanisms, including methods of reaching temperatures near absolute zero.