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Second-Law Aspects of Daily Life.tex
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\documentclass[10pt]{article} \usepackage{amssymb,amsmath} \usepackage[hmargin=2cm,vmargin=2cm]{geometry} \usepackage{cancel} \begin{document} {\large Second-Law Aspects of Daily Life}\\ \\ Thermodynamics is a fundamental natural science that deals with various aspects of energy, and even nontechnical people have a basic understanding of energy and the first law of thermodynamics since there is hardly any aspect of life that does not involve the transfer or transformation of energy in different forms. All the {\it dieters}, for example, base their lifestyle on the conservation of energy principle. Although the first-law aspects of thermodynamics are readily understood and easily accepted by most people, there is not a public awareness about the second law of thermodynamics, and the second-law aspects are not fully appreciated even by people with technical backgrounds. This causes some students to view the second law as something that is of theoretical interest rather than an important and practical engineering tool. As a result, students show 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 thermodynamics and miss the balanced, complete picture.\\ \\ Many {\it ordinary events} that go unnoticed can serve as excellent vehicles to convey important concepts of thermodynamics. Below we attempt to demonstrate the relevance of the second-law concepts such as exergy, reversible work, irreversibility, and the second-law efficiency to various aspects of daily life using examples with which even nontechnical people can identify. Hope fully, this will enhance our understanding and appreciation of the second law of thermodynamics and encourage us to use it more often in technical and even nontechnical areas. The critical reader is reminded that the concepts presented below are {\it soft} and {\it difficult to quantize}, and that they are offered here to stimulate interest in the study of the second law of thermodynamics and to enhance our understanding and appreciation of it.\\ \\ The second-law concepts are implicitly used in various aspects of daily life. Many successful people seem to make extensive use of them without even realizing it. There is growing awareness that quality plays as important a role as quantity in even ordinary daily activities. The following appeared in an article in the {\it Reno Gazette-Journal} on March 3, 1991: \begin{quote} \texttt Dr. Held considers himself a survivor of the tick-tock conspiracy. About four years ago, right around his 40th birthday, he was putting in 21-hour days -- working late, working out, taking care of his three children and getting involved in sports. He got about four or five hours of sleep a night \dots ``Now I'm in bed by 9:30 and I’m up by 6,'' he says. ``I get twice as much done as I used to. I don't have to do things twice or read things three times before I understand them.'' \end{quote} This statement has a strong relevance to the second-law discussions. It indicates that the problem is not how much time we have (the first law), but, rather, how effectively we use it (the second law). For a person to get {\it more done in less time} is no different than for a car to go {\it more miles on less fuel}.\\ \\ In thermodynamics, {\it reversible work} for a process is defined as the maxi mum useful work output (or minimum work input) for that process. It is the useful work that a system would deliver (or consume) during a process between two specified states if that process is executed in a reversible (perfect) manner. The difference between the reversible work and the actual useful work is due to imperfections and is called {\it irreversibility} (the wasted work potential). For the special case of the final state being the dead state or the state of the surroundings, the reversible work becomes a maximum and is called the {\it exergy} of the system at the initial state. The irreversibility for a reversible or perfect process is zero.\\ \\ The {\it exergy} of a person in daily life can be viewed as the best job that per son can do under the most favorable conditions. The {\it reversible work} in daily life, on the other hand, can be viewed as the best job a person can do under some specified conditions. Then the difference between the reversible work and the actual work done under those conditions can be viewed as the {\it irreversibility} or the {\it exergy destroyed}. In engineering systems, we try to identify the major sources of irreversibilities and minimize them in order to maximize performance. In daily life, a person should do just that to maxi mize his or her performance.\\ \\ The exergy of a person at a given time and place can be viewed as the maximum amount of work he or she can do at that time and place. Exergy is certainly difficult to quantify because of the interdependence of physical and intellectual capabilities of a person. The ability to perform physical and intellectual tasks simultaneously complicates things even further. {\it Schooling} and {\it training} obviously increase the exergy of a person. {\it Aging} decreases the physical exergy. Unlike most mechanical things, the exergy of human beings is a function of time, and the physical and/or intellectual exergy of a person goes to waste if it is not utilized at the time. A barrel of oil loses nothing from its exergy if left unattended for 40 years. However, a person will lose much of his or her entire exergy during that time period if he or she just sits back.\\ \\ A hard-working farmer, for example, may make full use of his {\it physical exergy} but very little use of his {\it intellectual exergy}. That farmer, for example, could learn a foreign language or a science by listening to some educational CDs at the same time he is doing his physical work. This is also true for people who spend considerable time in the car commuting to work. It is hoped that some day we will be able to do exergy analysis for people and their activities. Such an analysis will point out the way for people to mini mize their exergy destruction, and get more done in less time. Computers can perform several tasks at once. Why shouldn’t human beings be able to do the same?\\ \\ {\it Children} are bom with different levels of {\it exergies} (talents) in different areas. Giving aptitude tests to children at an early age is simply an attempt to uncover the extent of their ``hidden'' exergies, or talents. The children are then directed to areas in which they have the greatest exergy. As adults, they are more likely to perform at high levels without stretching the limits if they are naturally fit to be in that area.\\ \\ We can view the level of {\it alertness} of a person as his or her {\it exergy} for intellectual affairs. When a person is well-rested, the degree of alertness, and thus intellectual exergy, is at a maximum and this exergy decreases with time as the person gets tired, as illustrated in Fig. 8-19. Different tasks in daily life require different levels of intellectual exergy, and the difference between available and required alertness can be viewed as the {\it wasted alertness} or {\it exergy destruction}. To minimize exergy destruction, there should be a close match between available alertness and required alertness.\\ \\ Consider a well-rested student who is planning to spend her next 4 h studying and watching a 2-h-long movie. From the {\it first-law} point of view, it makes no difference in what order these tasks are performed. But from the {\it second-law} point of view, it makes a lot of difference. Of these two tasks, studying requires more intellectual alertness than watching a movie does, and thus it makes thermodynamic sense to study first when the alertness is high and to watch the movie later when the alertness is lower, as shown in the figure. A student who does it backwards wastes a lot of alertness while watching the movie, as illustrated in Fig. 8-19, and she has to keep going back and forth while studying because of insufficient alertness, thus getting less done in the same time period.\\ \\ In thermodynamics, the {\it first-law efficiency} (or thermal efficiency) of a heat engine is defined as the ratio of net work output to total heat input. That is, it is the fraction of the heat supplied that is converted to net work. In general, the first-law efficiency can be viewed as the ratio of the desired output to the required input. The first-law efficiency makes no reference to the {\it best possible performance}, and thus the first-law efficiency alone is not a realistic measure of performance. To overcome this deficiency, we defined the second-law efficiency, which is a measure of actual performance relative to the best possible performance under the same conditions. For heat engines, the second-law efficiency is defined as the ratio of the actual thermal efficiency to the maximum possible (reversible) thermal efficiency under the same conditions.\\ \\ In daily life, the {\it first-law efficiency} or {\it performance} of a person can be viewed as the accomplishment of that person relative to the effort he or she puts in. The {\it second-law efficiency} of a person, on the other hand, can be viewed as the performance of that person relative to the best possible performance under the circumstances.\\ \\ {\it Happiness} is closely related to the {\it second-law efficiency}. Small children are probably the happiest human beings because there is so little they can do, but they do it so well, considering their limited capabilities. That is, children have very high second-law efficiencies in their daily lives. The term ``full life'' also refers to second-law efficiency. A person is considered to have a full life, and thus a very high second-law efficiency, if he or she has utilized all of his or her abilities to the limit during a lifetime.\\ \\ Even a person with some disabilities has to put in considerably more effort to accomplish what a physically fit person accomplishes. Yet, despite accomplishing less with more effort, the person with disabilities who gives an impressive performance often gets more praise. Thus we can say that this person with disabilities had a low first-law efficiency (accomplishing little with a lot of effort) but a very high second-law efficiency (accomplishing as much as possible under the circumstances).\\ \\ In daily life, exergy can also be viewed as the {\it opportunities that we have} and the exergy destruction as the {\it opportunities wasted}. Time is the biggest asset that we have, and the time wasted is the wasted opportunity to do something useful (Fig. 8-50). \begin{quote} \texttt I have only just a minute,\\ Only 60 seconds in it,\\ Forced upon me -- can't refuse it\\ Didn't seek it, didn't choose it.\\ But it is up to me to use it.\\ I must suffer if I lose it.\\ Give account if I abuse it,\\ Just a tiny little minute --\\ But eternity is in it.\\ \\ (anonymous) \end{quote} The second law of thermodynamics also has interesting philosophical ramifications. Mass and energy are conserved quantities and are associated with the first law of thermodynamics, while entropy and exergy are non conserved quantities and are associated with the second law. The universe we perceive through our five senses consists of conserved quantities, and thus we tend to view the non-conserved quantities as being non-real and even out of this universe. The widely accepted big bang theory about the origin of the universe gave rise to the notion that this is an all-material uni verse, and everything is made of matter (more correctly, mass-energy) only. As conserved quantities, mass and energy fit into the description of truly physical quantities, but entropy and exergy do not since entropy can be created and exergy can be destroyed. Thus entropy and exergy are not truly physical quanities although they are closely related to the physical quantities of mass and energy. Therefore, the second law deals with quantities that are of a different kind of existence -- a universe in which things come into existence out of nothing and go out of existence into nothing -- and opens up a universe that is beyond the conserved all-material universe we know of.\\ \\ A similar argument can be given for the laws of nature that rule over matter. There is no question that both the first and the second laws of thermody namics exist, and these and other laws like Newton’s laws of motion govern the physical universe behind the scenes. As Alfred Montapert puts it, {\it ``Nature's laws are the invisible government of the earth.''} Albert Einstein expresses this phenomenon as {\it ``A spirit is manifest in the laws of the universe.''} Yet these laws that constitute the core of sciences cannot be sensed by our five senses and do not have a material existence, and thus they are not subject to the limitations of time and space. As such, the laws that seem to have infused all matter like a spirit rule everywhere, but they are not any where. It appears that quantities like entropy and exergy that come into exis tence out of nothing and go out of existence into nothing together with the laws of nature like the first and the second laws that govern the big-bang universe with an invisible powerful hand, are pointing the way for a broad ened definition of existence that is more in line with perceived and observed phenomena.\\ \\ The arguments presented here are exploratory in nature, and they are hoped to initiate some interesting discussions and research that may lead into better understanding of performance in various aspects of daily life. The second law may eventually be used to determine quantitatively the most effective way to improve the quality of life and performance in daily life, as it is presently used to improve the performance of engineering systems.\\ \\ {\bf THERMODYNAMICS -- An Engineering Approach (7th Ed.)}\\ YUNUS A. \c{C}ENGEL and MICHAEL A. BOLES\\ p.465-468 \end{document}