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Unformatted text preview: Chapter 7 Entropy Chapter 7 ENTROPY Entropy and the Increase of Entropy Principle 71C Yes. Because we used the relation ( Q H /T H ) = ( Q L /T L ) in the proof, which is the defining relation of absolute temperature. 72C No. The ∫ Q δ represents the net heat transfer during a cycle, which could be positive. 73C Yes. 74C No. A system may reject more (or less) heat than it receives during a cycle. The steam in a steam power plant, for example, receives more heat than it rejects during a cycle. 75C No. A system may produce more (or less) work than it receives during a cycle. A steam power plant, for example, produces more work than it receives during a cycle, the difference being the net work output. 76C The entropy change will be the same for both cases since entropy is a property and it has a fixed value at a fixed state. 77C No. In general, that integral will have a different value for different processes. However, it will have the same value for all reversible processes. 78C Yes. 79C That integral should be performed along a reversible path to determine the entropy change. 710C No. An isothermal process can be irreversible. Example: A system that involves paddlewheel work while losing an equivalent amount of heat. 711C The value of this integral is always larger for reversible processes. 712C No. Because the entropy of the surrounding air increases even more during that process, making the total entropy change positive. 713C It is possible to create entropy, but it is not possible to destroy it. 714C Sometimes. 715C Never. 716C Always. 71 Chapter 7 Entropy 717C Increase. 718C Increases. 719C Decreases. 720C Sometimes. 721C Yes. This will happen when the system is losing heat, and the decrease in entropy as a result of this heat loss is equal to the increase in entropy as a result of irreversibilities. 722C They are heat transfer, irreversibilities, and entropy transport with mass. 723C Greater than. 724 A rigid tank contains an ideal gas that is being stirred by a paddle wheel. The temperature of the gas remains constant as a result of heat transfer out. The entropy change of the gas is to be determined. Assumptions The gas in the tank is given to be an ideal gas. Analysis The temperature and the specific volume of the gas remain constant during this process. Therefore, the initial and the final states of the gas are the same. Then s 2 = s 1 since entropy is a property. Therefore, ∆ S sys = 72 IDEAL GAS 40 ° C Heat 30 ° C 200 kJ Chapter 7 Entropy 725 Air is compressed steadily by a compressor. The air temperature is maintained constant by heat rejection to the surroundings. The rate of entropy change of air is to be determined....
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 Spring '08
 Chung
 Thermodynamics, Energy, Entropy, entropy change, Qin, Ein Eout

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