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In thermodynamics, an isentropic process is an idealized thermodynamic process that is adiabatic and in which the work transfers of the system are frictionless; there is no transfer of heat or of matter and the process is reversible.〔. 〕〔Kestin, J. (1966). ''A Course in Thermodynamics'', Blaisdell Publishing Company, Waltham MA, p. 196.〕〔Münster, A. (1970). ''Classical Thermodynamics'', translated by E.S. Halberstadt, Wiley–Interscience, London, ISBN 0-471-62430-6, p. 13.〕〔Haase, R. (1971). Survey of Fundamental Laws, chapter 1 of ''Thermodynamics'', pages 1–97 of volume 1, ed. W. Jost, of ''Physical Chemistry. An Advanced Treatise'', ed. H. Eyring, D. Henderson, W. Jost, Academic Press, New York, lcn 73–117081, p. 71.〕〔Borgnakke, C., Sonntag., R.E. (2009). ''Fundamentals of Thermodynamics'', seventh edition, Wiley, ISBN 978-0-470-04192-5, p. 310.〕〔Massey, B.S. (1970), ''Mechanics of Fluids'', Section 12.2 (2nd edition) Van Nostrand Reinhold Company, London. Library of Congress Catalog Card Number: 67-25005, p. 19.〕 Such an idealized process is useful in engineering as a model of and basis of comparison for real processes.〔Çengel, Y.A., Boles, M.A. (2015). ''Thermodynamics: An Engineering Approach'', 8th edition, McGraw-Hill, New York, ISBN 978-0-07-339817-4, p. 340.〕 The word 'isentropic' is occasionally, though not customarily, interpreted in another way, reading it as if its meaning were deducible from its etymology. This is contrary to its original and customarily used definition. In this occasional reading, it means a process in which the entropy of the system remains unchanged, for example because work done on the system includes friction internal to the system, and heat is withdrawn from the system, in just the right amount to compensate for the internal friction, so as to leave the entropy unchanged.〔Çengel, Y.A., Boles, M.A. (2015). ''Thermodynamics: An Engineering Approach'', 8th edition, McGraw-Hill, New York, ISBN 978-0-07-339817-4, pp. 340–341.〕 == Background == The second law of thermodynamics states that, : where is the amount of energy the system gains by heating, is the temperature of the system, and is the change in entropy. The equal sign refers to a reversible process, which is an imagined idealized theoretical limit, never actually occurring in physical reality.〔Guggenheim, E.A. (1985). ''Thermodynamics. An Advanced Treatment for Chemists and Physicists'', seventh edition, North Holland, Amsterdam, ISBN 0444869514, p. 12: "As a limiting case between natural and unnatural processes we have reversible processes, which consist of the passage in either direction through a continuous series of equilibrium states. Reversible processes do not actually occur ...."〕〔Kestin, J. (1966). ''A Course in Thermodynamics'', Blaisdell Publishing Company, Waltham MA, p. 127: "However, by a stretch of imagination, it was accepted that a process, compression or expansion, as desired, could be performed "infinitely slowly" or as is sometimes said, ''quasistatically.''" P. 130: "It is clear that ''all natural processes are irreversible'' and that reversible processes constitute convenient idealizations only."〕 For an isentropic process, which by definition is reversible, there is no transfer of energy as heat because the process is adiabatic. In an irreversible process of transfer of energy as work, entropy is produced within the system; consequently, in order to maintain constant entropy within the system, energy must be removed from the system as heat during the process. For reversible processes, an isentropic transformation is carried out by thermally "insulating" the system from its surroundings. Temperature is the thermodynamic conjugate variable to entropy, thus the conjugate process would be an isothermal process in which the system is thermally "connected" to a constant-temperature heat bath. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Isentropic process」の詳細全文を読む スポンサード リンク
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