Thermodynamics

Chapter 8 | 465andW rev,in m 2 f 2 12323 kg2 1120.76 kJ>kg2 280,525 kJ 281 MJDiscussion Note that a minimum of 281 MJ of work input is required to fillthe tank with compressed air at 300 K and 1 MPa. In reality, the requiredwork input will be greater by an amount equal to the exergy destruction duringthe process. Compare this to the result of Example 8–7. What can youconclude?TOPIC OF SPECIAL INTEREST*Second-Law Aspects of Daily LifeThermodynamics is a fundamental natural science that deals with variousaspects of energy, and even nontechnical people have a basic understanding ofenergy and the first law of thermodynamics since there is hardly any aspect oflife that does not involve the transfer or transformation of energy in differentforms. All the dieters, for example, base their lifestyle on the conservation ofenergy principle. Although the first-law aspects of thermodynamics are readilyunderstood and easily accepted by most people, there is not a public awarenessabout the second law of thermodynamics, and the second-law aspects are notfully appreciated even by people with technical backgrounds. This causessome students to view the second law as something that is of theoretical interestrather than an important and practical engineering tool. As a result, studentsshow little interest in a detailed study of the second law of thermodynamics.This is unfortunate because the students end up with a one-sided view of thermodynamicsand miss the balanced, complete picture.Many ordinary events that go unnoticed can serve as excellent vehicles toconvey important concepts of thermodynamics. Below we attempt to demonstratethe relevance of the second-law concepts such as exergy, reversiblework, irreversibility, and the second-law efficiency to various aspects of dailylife using examples with which even nontechnical people can identify. Hopefully,this will enhance our understanding and appreciation of the second lawof thermodynamics and encourage us to use it more often in technical andeven nontechnical areas. The critical reader is reminded that the concepts presentedbelow are soft and difficult to quantize, and that they are offered hereto stimulate interest in the study of the second law of thermodynamics and toenhance our understanding and appreciation of it.The second-law concepts are implicitly used in various aspects of dailylife. Many successful people seem to make extensive use of them withouteven realizing it. There is growing awareness that quality plays as importanta role as quantity in even ordinary daily activities. The following appeared inan article in the Reno Gazette-Journal on March 3, 1991:Dr. Held considers himself a survivor of the tick-tock conspiracy. About fouryears ago, right around his 40th birthday, he was putting in 21-hour days—working late, working out, taking care of his three children and gettinginvolved in sports. He got about four or five hours of sleep a night. . . .*This section can be skipped without a loss in continuity.