Page 62 - Entrophy Analysis in Thermal Engineering Systems

54 Entropy Analysis in Thermal Engineering Systems

δQ δW¼dU with δQ¼TdS and δW¼pdV. For an ideal gas undergoing
an isothermal process, the first law is expressed as δQ¼δW so Eq. (1.19)
reduces to TdS¼pdV. In the absence of any work interaction (both external
and internal), Eq. (1.19) becomes dU¼TdS. If the process does not include
any heat (supplied externally or generated internally), the process is therefore
isentropic and Eq. (1.19) reduces to dU¼pdV. Finally, for a system that
experiences no form of work and heat, the change in the internal energy
is zero dU¼0.
The phenomenon of entropy increase (generation) is not merely corre-
lated with the irreversibility of the natural processes. It is rather an indicative
measure of the transference of energy in the form of heat, which may be
supplied from an external source, be generated internally by conversion
of work to heat, or be exchanged internally within a system. Interpreting
entropy generation as a measure of heat transfer may be considered as a more
accurate form of the energy dispersal view. The former takes into account
both the amount of heat and the temperature, whereas the latter accounts
only for spreading of energy without specifying the form of energy.

References
[1] J.C. Maxwell, Theory of Heat, Longmans Green & Co., London, 1902 pp. 162, 194.
[2] G.H. Bryan, Thermodynamics: An Introductory Treatise Dealing Mainly With First
Principles and Their Direct Applications, B. G. Teubner, Leipzig, 1907, pp. 71–74.
[3] G.A. Goodenough, Principles of Thermodynamics, second ed., Henry Hold & Co.,
New York, NY, 1914.
[4] J.P. Joule, On the changes of temperature produced by the rarefaction and condensation
of air, Philos. Mag. 26 (174) (1845) Ser. 3.
[5] W. Thomson, An account of Carnot’s theory of the motive power of heat; with numer-
ical results deduced from Regnault’s experiments on steam, Trans. Royal Soc. Edinb.,
Vo. XVI, Part I, 541–574.
[6] R. Clausius, The Mechanical Theory of Heat, Translated by W. R. Brown, MacMillan
& Co., London, 1879.
[7] B.F. Dodge, Chemical Engineering Thermodynamics, McGraw-Hill, New York,
1944, pp. 114–116.
[8] J.F. Klein, Physical Significance of Entropy or of the Second Law, Van Nostrand Com-
pany, (1910).
[9] A. Bejan, Thermodynamics today, Energy 160 (2018) 1208–1219.
[10] F.L. Lambert, Shuffled cards, messy desks, and disorderly dorm rooms—examples of
entropy increase? Nonsense, J. Chem. Educ. 76 (1999) 1385.
[11] H.S. Leff, Thermodynamic entropy: the spreading and sharing of energy, Am. J. Phys.
64 (1996) 1261–1271.
[12] F.L. Lambert, Disorder—a cracked crutch for supporting entropy discussions, J. Chem.
Educ. 79 (2002) 187–192.