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Exergy in Policy Development and Education
Chapter 25
Exergy in Policy Development and Education Chapter Outline 25.1 Introduction 25.2 Exergy Methods for Analysis and Design 25.3 The Role and Place for Exergy in Energy-Related Education and Awareness Policies 25.3.1 Public Understanding and Awareness of Energy 25.3.2 Public Understanding and Awareness of Exergy 25.3.3 Extending the Public’s Need to Understand and Be Aware of Exergy to Government and the Media
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25.4 The Role and Place for Exergy in Education Policies 25.4.1 Education about Exergy 25.4.2 The Need for Exergy Literacy in Scientists and Engineers 25.4.3 Understanding the Second Law through Exergy 25.4.4 Exergy’s Place in a Curriculum 25.5 Closing Remarks Problems
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ABSTRACT In this chapter, we describe the role of exergy in policy development and education. We examine education and awareness of exergy, by focusing first on the public and the media, and then on the education of thermodynamicists, as well as other technical people. Also, it is demonstrated that exergy has a place in policy development regarding energy-related education and awareness. It is demonstrated that the public is often confused when it discusses energy, needs to be better educated about exergy if energy issues and problems are to be addressed appropriately, and that a basic level of “exergy literacy” is needed among engineers and scientistsdparticularly those involved in decision making. KEYWORDS Exergy; Education; Policy; Design; Government; Media; Public.
25.1 INTRODUCTION It is important for the public to have a basic understanding, appreciation, and awareness of many technical issues. Such understanding and awareness fosters healthy public debate about problems and possible solutions, often helps guide how public funds are spent, and facilitates policy development. Energy issues are no exception. Yet, the public’s understanding of energy issues is often confused. In large part, this situation is attributable to the public having next to no understanding of exergy. In this chapter, we explain why such an understanding is necessary.
Exergy. http://dx.doi.org/10.1016/B978-0-08-097089-9.00025-5 Ó 2013 Ibrahim Dincer and Marc A. Rosen. Published by Elsevier Ltd. All rights reserved
It is easier for the public to be educated about and aware of exergy if students are adequately educated about exergy in appropriate venues (university and college thermodynamics courses, primary and secondary schools, etc.). Consequently, this chapter deals with education and awareness of exergy, first by focusing on the public and then by dwelling on the education of thermodynamicists as well as other technical people. The objective is to demonstrate that exergy has a place and role to play in policy development regarding energy-related education and awareness. Exergy can play a key role in developing appropriate and beneficial energy-related policies relating to education and awareness. Two main areas where exergy can have an impact on policies are discussed in this chapter: (1) public education and awareness and (2) student education. The former is more general, but is supported by the latter. Regarding public education and awareness about exergy, it appears that the public is often confused when it discusses energy, and needs to be better educated about exergy if energy issues and problems are to be addressed appropriately. Regarding the education of students about exergy, it appears that the coverage of exergy in thermodynamics education is often insufficient and inappropriate. Better coverage of exergy is needed to improve thermodynamics education and to make it more interesting to students, and a basic level of “exergy literacy” is needed among engineers and scientistsdparticularly those involved in decision making.
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25.2 EXERGY METHODS FOR ANALYSIS AND DESIGN Some features of exergy that are particularly pertinent to this chapter include: l
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When energy quality decreases, exergy is destroyed. Exergy is the “part” of energy that is useful to society, has economic value, and is thus worth managing carefully. A system has no exergy when it is in complete equilibrium with its environment. Then, no differences appear between the system and the environment in temperature, pressure, or constituent concentrations. The exergy of a system increases as the deviation of its state from that of the environment increases. For instance, hot water has a higher exergy content in winter than on a hot summer day, while a block of ice contains little exergy in winter but a significant quantity in summer.
Two simple examples well illustrate the attributes of exergy:
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Consider an adiabatic system containing fuel and air at ambient conditions. The fuel and air react to form a mixture of hot combustion gases. During the combustion process, the energy in the system remains fixed because it is adiabatic. But the exergy content declines as combustion proceeds due to the irreversibilities associated with the conversion of the highquality energy of fuel to the lower quality energy of combustion gases. The different behaviors of energy and exergy during this process are illustrated qualitatively in Figure 25.1. A mineral deposit “contrasts” with the environment of the earth, and is thus a carrier of exergy. This contrast increases with the concentration of the mineral, as shown in Figure 25.2. When the mineral is mined, its exergy content is low or zero (depending on the concentration of the mineral in the environmental
FIGURE 25.1 Qualitative comparison of energy and exergy during combustion.
Energy or exergy (relative units)
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deposit) while the exergy content increases if its concentration is enriched. A poorer mineral deposit contains less exergy than a concentrated one. Conversely, when a concentrated mineral is dispersed in the environment, its exergy content decreases. As pointed out throughout this book, exergy analysis, a methodology for the analysis, design, and improvement of energy and other systems, is useful for improving the efficiency of energy-resource use. Exergy has many other implications on, and links with, other disciplines, as discussed in detail in previous chapters. A link exists between exergy and environmental impact and sustainability. Energy production, transformation, transport, and use all impact on earth’s environment. The exergy of a quantity of energy or a substance can be viewed as a measure of its usefulness, quality, or potential to cause change. Exergy appears to be an effective measure of the potential of a substance to impact the environment. This link between exergy and environmental impact is particularly significant since energy and environment policies are likely to play an increasingly prominent role in the future in a broad range of local, regional, and global environmental concerns. The tie between exergy and the environment has implications regarding environmental impact and has been investigated previously by several researchers, including the authors. Exergy is a useful concept in economics. In macroeconomics, exergy offers a way to reduce resource depletion and environmental destruction by exergy taxes or rebates. In microeconomics, exergy has been combined beneficially with cost-benefit analysis to improve designs. By minimizing life cycle cost, we find the “best” system given prevailing economic conditions and, by minimizing exergy losses, we also minimize environmental effects. Finally, exergy has been proposed as an important consideration in policy making related to energy. This chapter expands this area by focusing specifically on education and awareness.
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Exergy in Policy Development and Education
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Concentration of mineral (%) FIGURE 25.2 Qualitative variation of the exergy of a mineral with concentration.
25.3 THE ROLE AND PLACE FOR EXERGY IN ENERGY-RELATED EDUCATION AND AWARENESS POLICIES Before considering understanding and awareness of exergy by the public, and its role and place in energy-related education and awareness policies, it is informative to consider the public’s understanding and awareness of the more conventional quantity energy.
25.3.1 Public Understanding and Awareness of Energy The typical layperson hears of energy and energy issues daily, and is generally comfortable with receiving that energy-related information and feels he or she follows it. He or she even understands it, or at least thinks he/she does. This sense of comfort and understanding exists despite all of the problems associated with energy. For instance, consider the following: l
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Efficiencies based on energy can often be non-meaningful or even misleading, because energy efficiency is not a consistent measure of how nearly a process approaches ideality. For instance, the energy efficiency of electric space heating is high (nearly 100%) even though the process is far from ideal. The fact that the same space heat can be delivered by an electric heat pump using much less electricity than the electric space heater corroborates this observation. Losses of energy can be large in quantity when they are, in fact, not that significant thermodynamically due to the low quality or usefulness of the energy that is lost. For example, the waste heat exiting a power plant via cooling water has a lot of energy, but little exergy (because its state is near to that of the environment).
25.3.2 Public Understanding and Awareness of Exergy An understanding of exergy, similar to that which exists for energy, is almost entirely nonexistent in lay members of the public. This lack of understanding exists despite the fact that exergy overcomes many of the deficiencies of energy methods described previously. Worse still, the public is often confused when it refers to energy. To those who deal with exergy, it often seems that members of the public actually mean exergy when they say energy. For example, two respected exergy researchers, Wepfer and Gaggioli (1980), begin an article with “Exergy . is synonymous with what the layman calls ‘energy.’ It is exergy, not energy, that is the resource of value, and it is this commodity, that ‘fuels’ processes, which the layman is willing to pay for.” These points illustrate why it is essential that the public developdor be helped to developda basic understanding of exergy. The level of understanding needed by the public about exergy should at least be comparable to that for energy. To help illustrate these contentions, some examples of the problems associated with a lack of knowledge of exergy by the public are outlined in the following: l
One example of the confusion exhibited by the public when speaking of energy is the well-used term energy conservation. When members of the public say energy conservation, they are usually referring to an objective of efforts to solve energy problems. Yet the term energy conservation is meaningless in that regard, in that it simply states the First Law of Thermodynamics. Exergy, however, is not conserved and it appears that what the public is really interested in conserving is exergy, the potential to drive processes and systems that deliver services or products.
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Another example of confusion in the public surrounds the drive for increased energy efficiency. Energy efficiencies do not necessarily provide a measure of how nearly a process approaches ideality, yet that is what the public means by energy efficiency. Exergy efficiencies do provide measures of approach to ideality, and so it appears that the public means increased exergy efficiency when discussing increased energy efficiency. A third example of the problems that can develop when the public does not have knowledge of exergy, but retains only a confused understanding of energy, relates to the energy crisis. For instance, during the energy crisis of the 1970s, oil scarcities existed due to reductions in oil production. Most of the energy that was available to the public before the crisis was available during it. For instance, huge amounts of solar energy continued to stream into the earth every day. Waste thermal energy was continually emitted from facilities and buildings. The commodity for which there was a crisis, therefore, appeared to be exergy, not energy. That is, energy forms capable of delivering a wide range of energy services (like oil), which have high exergies, were in short supply. Of course, there were also other issues related to the energy crisis, particularly the shortage of reasonably inexpensive and widely available resources. But, the key point here is that the crisis was about exergy, not energy, yet the public referred to the situation as an energy crisis. A fourth example of public confusion about energy relates to the oft-pronounced need for energy security. If it were simply energy for which we desire a secure supply, there would be no real problem. We have energy in abundance available in our environment and even when we use energy we still have equivalent quantities of energy left over because our use is really only energy conversion or transformation. However, we are not concerned about ensuring secure supplies of energy; instead we are concerned about only those resources that are useful to us, that can be used to provide a wide range of energy services, and that can satisfy all our energy-related needs and desires. That is, we are concerned with having secure supplies of exergy, or what might be called exergy security.
The lack of clarity regarding the points raised in these four examples has been discussed in more detail previously, focusing on scientists, engineers, and other technical readers. This discussion, however, is intended to raise these points in a different context, and emphasize that this lack of clarity extends to the public, where the problems caused are different, but perhaps are just as, or more, important.
25.3.3 Extending the Public’s Need to Understand and Be Aware of Exergy to Government and the Media By extension of the previous arguments, government officials require a rudimentary understanding of exergy to improvedor at least complementdtheir understanding of energy issues. This understanding can help guide the development of rational energy policies. Government, being another type of reflection of the public, will be far less prone to use exergy methods, even when they can be beneficial, if it feels that the public does not understand exergy even in the simplest way and therefore will not appreciate government efforts. The importance of such government involvement should not be understated and has been investigated by researchers. For example, Wall (1993) alluded to the importance of exergy in relation to democracy in an article that dealt with the dilemmas of modern society. There have also been some successes in incorporating exergy into government policies. For instance, Favrat et al. (2008) reported on the introduction of an exergy indicator in a local law on energy in Switzerland’s Canton of Geneva. Through that law, which governs the attribution of building permits for new or retrofitted city areas, the application procedure requires the calculation of an exergy indicator for large projects. Similarly, members of the mediadincluding the press, television, and radiodneed to be informed, at least at a basic level, about exergy and its roles. In a sense, the media are a reflection of the public. If the media have an appreciation of exergy, they can help ensure that the public has an understanding about exergy. Educating via television, in particular, can be an especially powerful method for increasing public awareness about exergy. However, for the press and media to run exergy-related articles, it requires that the public has a rudimentary understanding of, and interest in, exergy matters. Otherwise, the press and media tend to neglect exergy-related topics for fear of boring or confusing the public. A first step to resolving the reluctance of the press to write about exergy is education. The next section of this article focuses on educating students about exergy, which is one manner of directly and indirectly educating the public, in the long run, about exergy.
25.4 THE ROLE AND PLACE FOR EXERGY IN EDUCATION POLICIES Thermodynamics education is often thought of as a mature discipline, yet it remains the subject of continual debate. The emergence of exergy methods as important elements and tools of thermodynamics has provided additional
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Exergy in Policy Development and Education
subject matter for dialog, especially regarding the role and place for exergy in curricula.
25.4.1 Education about Exergy The impact of exergy on the teaching of thermodynamics has been and continues to be significant. Developments in this area abound. For instance, Bejan (2001) noted in an editorial in the inaugural issue of Exergy, An International Journal, “As the new century begins, we are witnessing revolutionary changes in the way thermodynamics is taught.” Further on, he observed that “the methods of exergy analysis . are the most visible and established forms of this change.” One point of contention is whether present coverage of exergy in thermodynamics education is sufficient and appropriate. Views on this issue are often not in agreement. Exergy, where it forms part of the curriculum, is normally taught at the college and university levels. However, many feel that it should be covered in primary and/or secondary education levels. That point is also disputed. Most of the remainder of this section focuses on college and university levels, since exergy is normally taught at the post-secondary level. In some ways and at some schools, present coverage of exergy is sufficient. Some evidence to support this claim includes the following: l
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Several articles have appeared in the engineering and education literature on teaching exergy analysis. For instance, Cengel (1996) proposed “a ‘physical’ or ‘intuitive’ approach . as an alternative to the current ‘formula based’ approach to learning thermodynamics” and incorporated exergy into the approach. Dunbar and Lior (1992) recommended an exergy-based approach to teaching energy systems. They noted that the approach highlights “important conclusions from exergy analysis, not obtainable from the conventional energy analysis.” In addition, they felt that “the approach evoked the intellectual curiosity of students and increased their interest in the course.” Most texts on thermodynamics have, over the last few decades, incorporated sections or chapters on exergy methods. Even in 1988, while commenting on the increased attention being paid to exergy analysis, Bejan (1988) pointed out that, “every new undergraduate engineering thermodynamics textbook has at least one chapter on the subject.” Several excellent texts devoted to exergy analysis have been published, including particularly useful ones, such as by Kotas (1995), Edgerton (1992), and Szargut et al. (1988).
Such materials have made it easier to expand the coverage of exergy in thermodynamics courses. Yet, in
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general, room exists for improvement in the area of exergy coverage in thermodynamics education, and efforts should be made to achieve these improvements. Three points related to improving thermodynamics education through better coverage of exergy are addressed in the following three subsections.
25.4.2 The Need for Exergy Literacy in Scientists and Engineers We need to ensure that our education systems provide all students who study thermodynamics with a good grounding in exergy. For exergy methods to become more widely used and beneficially exploited, those who study and work in technical fieldsdparticularly where thermodynamics is applieddshould have a basic understanding of exergy. In addition, technical managers and decision makers require at least an appreciation of what exergy is and how it is used, if they are to make proper decisions on matters where exergy is, or should be, considered. Some may suggest that we do not, for practical purposes, need such an understanding of exergy among technical personnel. Some examples help refute such suggestions: l
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Research proposals have at times not been funded, in large part because exergy methods formed part of the approach. On reading the comments of reviewers of such proposals, it is sometimes evident that the reviewers have read energy in place of exergy throughout the proposalsdrendering them utterly meaningless. This result can occur despite the fact that great pains are often taken within proposals to emphasize the need to use exergy methods. What perhaps remains most disconcerting is that, in many of these instances, the reviewers have technical backgrounds. Government officials or company managers have admitted to exergy researchers and practitioners that, in many instances, they chose not to use exergy on a project or activity, not because an exergy approach was unsuitable, but because they did not understand it or had never heard of it. This situation is problematic because decision making, when it is based on avoiding topics about which one is ignorant, cannot be productive.
We consequently feel in general that a strong need exists to improve the “exergy literacy” of engineers and scientists.
25.4.3 Understanding the Second Law through Exergy The Second Law of Thermodynamics (SLT) often makes students of thermodynamics fearful. Introducing the concept of entropy usually only increases their trepidation. Even students who pass courses on thermodynamics and ultimately
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graduate often retain fears of the SLT and entropy and feel they do not really understand these topics. Ahrendts (1980), for example, begins one of his articles on exergy methods with “Thermodynamics is not a very popular science, because the concepts in thermodynamics do not conform to the unsophisticated human experience.” Focusing on the SLT he continues “Traditional formulations of the Second Law prevent a simple understanding of energy conversions, because the application of the entropy concept to those processes is often looked upon as a miracle.” Others also have agreed with these concerns and developed different approaches to teaching the SLT. One example is a thermodynamics text by Dixon (1975), the preface of which states “entropy is [not] the most significant or useful aspect of the Second Law” and “the Second Law has to do with the concept of degradation of energy; that is, with loss of useful work potential.” Dixon introduces the SLT through the concept of degradation of energy, claiming “degradation . because it is a work term, is an easily grasped concept.” By focusing on degradation of energy rather than the abstract property entropy, Dixon feels his book results in “a clearer physical meaning for entropy.” This approach, although instructive for some, is still somewhat abstract and vague. The approach comes close to teaching the SLT through exergy, and would likely be clearer if it did so. Exergy provides a perspective of the SLT and entropy that is much more intuitively understandable to students. The definition of exergy, which states that exergy is the maximum work that can be obtained from a system or flow within a reference environment, is usually much more straightforward than the definition of entropy. Also, characteristics of exergydsuch as it being a nonconserved quantitydare normally easier for students to grasp than the concepts surrounding entropy and its characteristics. Thus, we feel that exergy should generally form a central component of thermodynamics courses. More specifically, exergy should play a significant role in dealing with and teaching the SLT. Such an approach would likely make the SLT more understandable and practical and less fear inspiring. Some readers will point out correctly that there exist some additional complexities when dealing with exergy rather than entropy (e.g., a reference environment must be introduced and defined). Nevertheless, we believe that the overall benefits of approaching the SLT through exergy outweigh the difficulties.
graduate level. In the latter case, the rationale often provided is that students need a firm grounding in traditional thermodynamics before they deal with exergy. Those who support including exergy as a part of the undergraduate curriculum, on the other hand, claim this approach is necessary because exergy forms a critical and important part of basic thermodynamics. Further support for this argument is added by earlier statements in this article about exergy providing a preferable approach to dealing with and teaching the SLT. Although there is likely some merit in each of the rationales for different placements of exergy in curricula, this author nevertheless believes that some coverage of exergy should be required in all undergraduate courses in engineering thermodynamics. Beyond such a core of exergy material, however, there are multiple ways in which additional exergy material can be incorporated into engineering curricula at undergraduate or graduate levels. Exergy methods can also be incorporated into courses that apply to thermodynamics. In Thermal Design and Optimization, for instance, Bejan et al. (1996) feature a substantial amount of material on exergy and related methods. They explain in the preface that they include exergy in the text “because an increasing number of engineers and engineering managers worldwide agree that it has considerable merit and are advocating its use.” They state further that their aim in featuring exergy and related methods is “to contribute to the education of the next generation of thermal system designers and to the background of currently active designers who feel the need for more effective design methods.” These authors clearly regard exergy as a critical component in thermal design education, whose importance will only increase in the future. Much room for debate exists about the place for exergy in a curriculum. Perhaps no single answer exists, and each approach will retain its proponents. Some engineering thermodynamics curricula, to their detriment, do not cover exergy at all, but these are likely in the minority. The range of views on how exergy can and should be incorporated into a thermodynamics curriculum is sufficiently diverse that a consensus on the best approach is almost certainly not possible in the near term. It is even questionable whether a consensus can be reached in the long term, after exergy methods mature. Two points help illustrate this view:
25.4.4 Exergy’s Place in a Curriculum
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A challenging issue is where exergy should be covered in a curriculum. In engineering programs, for example, exergy is sometimes covered lightly in thermodynamics courses at the undergraduate level. Sometimes exergy is covered separately, as either a core or an elective undergraduate course, while in some schools exergy is only covered at the
A panel session on The Second Law in Engineering Education was held within the Symposium on Thermodynamics and the Design, Analysis, and Improvement of Energy Systems, at the 1996 International Mechanical Engineering Congress and Exposition of the American Society of Mechanical Engineers (El-Sayed et al., 1997). Among the topics covered were whether or not undergraduate engineers need to be educated in the SLT
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and how much depth is required in this area. The panelists included representatives of academia and industry, as well as respected thermodynamicists and exergy proponents. Although several opinions were expressed on the need to include exergy methods in the teaching of the SLT, the views expressed varied greatlydemphasizing the difficulties in reaching a consensus on the best approach for incorporating exergy into a thermodynamics curriculum. Consideration of the nomenclature and terminology of exergy analysis reveals that a diversity of names and symbols presently exist for the same quantities in exergy analysis. This situation persists despite efforts to reach a common nomenclature and terminology. This weakness demonstrates how difficult it is to reach a consensus just on the relatively narrow topic of nomenclature and terminology, not to mention reaching a consensus on the broader topic of incorporating exergy into a thermodynamics curriculum.
25.5 CLOSING REMARKS The key elements of this chapter are awareness, understanding, and education as they relate to exergy and its role in policy making. The relation between these key elements is illustrated in Figure 25.3. There, it is shown that an understanding and awareness of exergy requires, for all people, education. The types of education that are appropriate for
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technical persons such as engineers and scientists are shown to be different from those that are appropriate for nontechnical persons such as members of the public, government, or media. But, in a general sense, the factors involved in raising awareness and understanding are similar conceptually, and differ mainly in depth and rigor of treatment. The arguments presented in this chapter demonstrate that the public is often confused when discussing energy and a need exists to improve public understanding and awareness of exergy. Such understanding and awareness is essential if we are to better address the energy issues and problems of today and tomorrow. Thus, exergy can play a key role in developing appropriate and beneficial energyrelated policies, but exploiting the potential of exergy requires appropriate support for public education and awareness about exergy. In support of the need for public understanding and awareness of exergy, it should take on a prominent place in thermodynamics courses. Beyond elucidating the concepts of the SLT and entropy, such an approach can help ensure a rudimentary understanding of exergy in all technical personnel. An approach based on exergy could make the SLT more interesting, appealing, and practical, as well as less daunting and confusing. Then, it may be easier to improve general understanding of exergy in the scientific and engineering communities, as well as the general public, by ensuring that a basic level of “exergy literacy” exists among engineers and scientistsdparticularly those involved in decision making. Education policies that support
Awareness and understanding of exergy
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FIGURE 25.3 Illustration of the importance of education in building awareness and understanding of exergy among different categories of people.
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inclusion of exergy in relevant curricula, at all appropriate education levels, should be considered.
PROBLEMS 25.1 Conduct research to determine if thermodynamics textbooks written several decades ago cover exergy and to what extent. 25.2 Almost all present undergraduate thermodynamics textbooks have at least one chapter devoted to exergy. If you were the instructor of a single thermodynamics course and you could only cover some of the chapters, would you cover exergy? Provide reasons for your answer.
Exergy
25.3 Do you favor changing the way thermodynamics is taught by adopting an exergy-based approach? Why? 25.4 Explain how a better understanding of exergy by engineering students can help improve public awareness of exergy. 25.5 Explain how exergy is a useful tool in policy making related to energy. Provide examples. 25.6 Is it realistic to expect that the level of understanding of the public about exergy should be comparable to that for energy? Explain. 25.7 Explain how a better understanding and appreciation of exergy by the public and by policy makers can help foster more efficient use of energy sources and minimize their effects on environment.
Exergy in Policy Development and Education Chapter Outline 25.1 Introduction 25.2 Exergy Methods for Analysis and Design 25.3 The Role and Place for Exergy in Energy-Related Education and Awareness Policies 25.3.1 Public Understanding and Awareness of Energy 25.3.2 Public Understanding and Awareness of Exergy 25.3.3 Extending the Public’s Need to Understand and Be Aware of Exergy to Government and the Media
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25.4 The Role and Place for Exergy in Education Policies 25.4.1 Education about Exergy 25.4.2 The Need for Exergy Literacy in Scientists and Engineers 25.4.3 Understanding the Second Law through Exergy 25.4.4 Exergy’s Place in a Curriculum 25.5 Closing Remarks Problems
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ABSTRACT In this chapter, we describe the role of exergy in policy development and education. We examine education and awareness of exergy, by focusing first on the public and the media, and then on the education of thermodynamicists, as well as other technical people. Also, it is demonstrated that exergy has a place in policy development regarding energy-related education and awareness. It is demonstrated that the public is often confused when it discusses energy, needs to be better educated about exergy if energy issues and problems are to be addressed appropriately, and that a basic level of “exergy literacy” is needed among engineers and scientistsdparticularly those involved in decision making. KEYWORDS Exergy; Education; Policy; Design; Government; Media; Public.
25.1 INTRODUCTION It is important for the public to have a basic understanding, appreciation, and awareness of many technical issues. Such understanding and awareness fosters healthy public debate about problems and possible solutions, often helps guide how public funds are spent, and facilitates policy development. Energy issues are no exception. Yet, the public’s understanding of energy issues is often confused. In large part, this situation is attributable to the public having next to no understanding of exergy. In this chapter, we explain why such an understanding is necessary.
Exergy. http://dx.doi.org/10.1016/B978-0-08-097089-9.00025-5 Ó 2013 Ibrahim Dincer and Marc A. Rosen. Published by Elsevier Ltd. All rights reserved
It is easier for the public to be educated about and aware of exergy if students are adequately educated about exergy in appropriate venues (university and college thermodynamics courses, primary and secondary schools, etc.). Consequently, this chapter deals with education and awareness of exergy, first by focusing on the public and then by dwelling on the education of thermodynamicists as well as other technical people. The objective is to demonstrate that exergy has a place and role to play in policy development regarding energy-related education and awareness. Exergy can play a key role in developing appropriate and beneficial energy-related policies relating to education and awareness. Two main areas where exergy can have an impact on policies are discussed in this chapter: (1) public education and awareness and (2) student education. The former is more general, but is supported by the latter. Regarding public education and awareness about exergy, it appears that the public is often confused when it discusses energy, and needs to be better educated about exergy if energy issues and problems are to be addressed appropriately. Regarding the education of students about exergy, it appears that the coverage of exergy in thermodynamics education is often insufficient and inappropriate. Better coverage of exergy is needed to improve thermodynamics education and to make it more interesting to students, and a basic level of “exergy literacy” is needed among engineers and scientistsdparticularly those involved in decision making.
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25.2 EXERGY METHODS FOR ANALYSIS AND DESIGN Some features of exergy that are particularly pertinent to this chapter include: l
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When energy quality decreases, exergy is destroyed. Exergy is the “part” of energy that is useful to society, has economic value, and is thus worth managing carefully. A system has no exergy when it is in complete equilibrium with its environment. Then, no differences appear between the system and the environment in temperature, pressure, or constituent concentrations. The exergy of a system increases as the deviation of its state from that of the environment increases. For instance, hot water has a higher exergy content in winter than on a hot summer day, while a block of ice contains little exergy in winter but a significant quantity in summer.
Two simple examples well illustrate the attributes of exergy:
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Consider an adiabatic system containing fuel and air at ambient conditions. The fuel and air react to form a mixture of hot combustion gases. During the combustion process, the energy in the system remains fixed because it is adiabatic. But the exergy content declines as combustion proceeds due to the irreversibilities associated with the conversion of the highquality energy of fuel to the lower quality energy of combustion gases. The different behaviors of energy and exergy during this process are illustrated qualitatively in Figure 25.1. A mineral deposit “contrasts” with the environment of the earth, and is thus a carrier of exergy. This contrast increases with the concentration of the mineral, as shown in Figure 25.2. When the mineral is mined, its exergy content is low or zero (depending on the concentration of the mineral in the environmental
FIGURE 25.1 Qualitative comparison of energy and exergy during combustion.
Energy or exergy (relative units)
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deposit) while the exergy content increases if its concentration is enriched. A poorer mineral deposit contains less exergy than a concentrated one. Conversely, when a concentrated mineral is dispersed in the environment, its exergy content decreases. As pointed out throughout this book, exergy analysis, a methodology for the analysis, design, and improvement of energy and other systems, is useful for improving the efficiency of energy-resource use. Exergy has many other implications on, and links with, other disciplines, as discussed in detail in previous chapters. A link exists between exergy and environmental impact and sustainability. Energy production, transformation, transport, and use all impact on earth’s environment. The exergy of a quantity of energy or a substance can be viewed as a measure of its usefulness, quality, or potential to cause change. Exergy appears to be an effective measure of the potential of a substance to impact the environment. This link between exergy and environmental impact is particularly significant since energy and environment policies are likely to play an increasingly prominent role in the future in a broad range of local, regional, and global environmental concerns. The tie between exergy and the environment has implications regarding environmental impact and has been investigated previously by several researchers, including the authors. Exergy is a useful concept in economics. In macroeconomics, exergy offers a way to reduce resource depletion and environmental destruction by exergy taxes or rebates. In microeconomics, exergy has been combined beneficially with cost-benefit analysis to improve designs. By minimizing life cycle cost, we find the “best” system given prevailing economic conditions and, by minimizing exergy losses, we also minimize environmental effects. Finally, exergy has been proposed as an important consideration in policy making related to energy. This chapter expands this area by focusing specifically on education and awareness.
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Concentration of mineral (%) FIGURE 25.2 Qualitative variation of the exergy of a mineral with concentration.
25.3 THE ROLE AND PLACE FOR EXERGY IN ENERGY-RELATED EDUCATION AND AWARENESS POLICIES Before considering understanding and awareness of exergy by the public, and its role and place in energy-related education and awareness policies, it is informative to consider the public’s understanding and awareness of the more conventional quantity energy.
25.3.1 Public Understanding and Awareness of Energy The typical layperson hears of energy and energy issues daily, and is generally comfortable with receiving that energy-related information and feels he or she follows it. He or she even understands it, or at least thinks he/she does. This sense of comfort and understanding exists despite all of the problems associated with energy. For instance, consider the following: l
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Efficiencies based on energy can often be non-meaningful or even misleading, because energy efficiency is not a consistent measure of how nearly a process approaches ideality. For instance, the energy efficiency of electric space heating is high (nearly 100%) even though the process is far from ideal. The fact that the same space heat can be delivered by an electric heat pump using much less electricity than the electric space heater corroborates this observation. Losses of energy can be large in quantity when they are, in fact, not that significant thermodynamically due to the low quality or usefulness of the energy that is lost. For example, the waste heat exiting a power plant via cooling water has a lot of energy, but little exergy (because its state is near to that of the environment).
25.3.2 Public Understanding and Awareness of Exergy An understanding of exergy, similar to that which exists for energy, is almost entirely nonexistent in lay members of the public. This lack of understanding exists despite the fact that exergy overcomes many of the deficiencies of energy methods described previously. Worse still, the public is often confused when it refers to energy. To those who deal with exergy, it often seems that members of the public actually mean exergy when they say energy. For example, two respected exergy researchers, Wepfer and Gaggioli (1980), begin an article with “Exergy . is synonymous with what the layman calls ‘energy.’ It is exergy, not energy, that is the resource of value, and it is this commodity, that ‘fuels’ processes, which the layman is willing to pay for.” These points illustrate why it is essential that the public developdor be helped to developda basic understanding of exergy. The level of understanding needed by the public about exergy should at least be comparable to that for energy. To help illustrate these contentions, some examples of the problems associated with a lack of knowledge of exergy by the public are outlined in the following: l
One example of the confusion exhibited by the public when speaking of energy is the well-used term energy conservation. When members of the public say energy conservation, they are usually referring to an objective of efforts to solve energy problems. Yet the term energy conservation is meaningless in that regard, in that it simply states the First Law of Thermodynamics. Exergy, however, is not conserved and it appears that what the public is really interested in conserving is exergy, the potential to drive processes and systems that deliver services or products.
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Another example of confusion in the public surrounds the drive for increased energy efficiency. Energy efficiencies do not necessarily provide a measure of how nearly a process approaches ideality, yet that is what the public means by energy efficiency. Exergy efficiencies do provide measures of approach to ideality, and so it appears that the public means increased exergy efficiency when discussing increased energy efficiency. A third example of the problems that can develop when the public does not have knowledge of exergy, but retains only a confused understanding of energy, relates to the energy crisis. For instance, during the energy crisis of the 1970s, oil scarcities existed due to reductions in oil production. Most of the energy that was available to the public before the crisis was available during it. For instance, huge amounts of solar energy continued to stream into the earth every day. Waste thermal energy was continually emitted from facilities and buildings. The commodity for which there was a crisis, therefore, appeared to be exergy, not energy. That is, energy forms capable of delivering a wide range of energy services (like oil), which have high exergies, were in short supply. Of course, there were also other issues related to the energy crisis, particularly the shortage of reasonably inexpensive and widely available resources. But, the key point here is that the crisis was about exergy, not energy, yet the public referred to the situation as an energy crisis. A fourth example of public confusion about energy relates to the oft-pronounced need for energy security. If it were simply energy for which we desire a secure supply, there would be no real problem. We have energy in abundance available in our environment and even when we use energy we still have equivalent quantities of energy left over because our use is really only energy conversion or transformation. However, we are not concerned about ensuring secure supplies of energy; instead we are concerned about only those resources that are useful to us, that can be used to provide a wide range of energy services, and that can satisfy all our energy-related needs and desires. That is, we are concerned with having secure supplies of exergy, or what might be called exergy security.
The lack of clarity regarding the points raised in these four examples has been discussed in more detail previously, focusing on scientists, engineers, and other technical readers. This discussion, however, is intended to raise these points in a different context, and emphasize that this lack of clarity extends to the public, where the problems caused are different, but perhaps are just as, or more, important.
25.3.3 Extending the Public’s Need to Understand and Be Aware of Exergy to Government and the Media By extension of the previous arguments, government officials require a rudimentary understanding of exergy to improvedor at least complementdtheir understanding of energy issues. This understanding can help guide the development of rational energy policies. Government, being another type of reflection of the public, will be far less prone to use exergy methods, even when they can be beneficial, if it feels that the public does not understand exergy even in the simplest way and therefore will not appreciate government efforts. The importance of such government involvement should not be understated and has been investigated by researchers. For example, Wall (1993) alluded to the importance of exergy in relation to democracy in an article that dealt with the dilemmas of modern society. There have also been some successes in incorporating exergy into government policies. For instance, Favrat et al. (2008) reported on the introduction of an exergy indicator in a local law on energy in Switzerland’s Canton of Geneva. Through that law, which governs the attribution of building permits for new or retrofitted city areas, the application procedure requires the calculation of an exergy indicator for large projects. Similarly, members of the mediadincluding the press, television, and radiodneed to be informed, at least at a basic level, about exergy and its roles. In a sense, the media are a reflection of the public. If the media have an appreciation of exergy, they can help ensure that the public has an understanding about exergy. Educating via television, in particular, can be an especially powerful method for increasing public awareness about exergy. However, for the press and media to run exergy-related articles, it requires that the public has a rudimentary understanding of, and interest in, exergy matters. Otherwise, the press and media tend to neglect exergy-related topics for fear of boring or confusing the public. A first step to resolving the reluctance of the press to write about exergy is education. The next section of this article focuses on educating students about exergy, which is one manner of directly and indirectly educating the public, in the long run, about exergy.
25.4 THE ROLE AND PLACE FOR EXERGY IN EDUCATION POLICIES Thermodynamics education is often thought of as a mature discipline, yet it remains the subject of continual debate. The emergence of exergy methods as important elements and tools of thermodynamics has provided additional
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subject matter for dialog, especially regarding the role and place for exergy in curricula.
25.4.1 Education about Exergy The impact of exergy on the teaching of thermodynamics has been and continues to be significant. Developments in this area abound. For instance, Bejan (2001) noted in an editorial in the inaugural issue of Exergy, An International Journal, “As the new century begins, we are witnessing revolutionary changes in the way thermodynamics is taught.” Further on, he observed that “the methods of exergy analysis . are the most visible and established forms of this change.” One point of contention is whether present coverage of exergy in thermodynamics education is sufficient and appropriate. Views on this issue are often not in agreement. Exergy, where it forms part of the curriculum, is normally taught at the college and university levels. However, many feel that it should be covered in primary and/or secondary education levels. That point is also disputed. Most of the remainder of this section focuses on college and university levels, since exergy is normally taught at the post-secondary level. In some ways and at some schools, present coverage of exergy is sufficient. Some evidence to support this claim includes the following: l
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Several articles have appeared in the engineering and education literature on teaching exergy analysis. For instance, Cengel (1996) proposed “a ‘physical’ or ‘intuitive’ approach . as an alternative to the current ‘formula based’ approach to learning thermodynamics” and incorporated exergy into the approach. Dunbar and Lior (1992) recommended an exergy-based approach to teaching energy systems. They noted that the approach highlights “important conclusions from exergy analysis, not obtainable from the conventional energy analysis.” In addition, they felt that “the approach evoked the intellectual curiosity of students and increased their interest in the course.” Most texts on thermodynamics have, over the last few decades, incorporated sections or chapters on exergy methods. Even in 1988, while commenting on the increased attention being paid to exergy analysis, Bejan (1988) pointed out that, “every new undergraduate engineering thermodynamics textbook has at least one chapter on the subject.” Several excellent texts devoted to exergy analysis have been published, including particularly useful ones, such as by Kotas (1995), Edgerton (1992), and Szargut et al. (1988).
Such materials have made it easier to expand the coverage of exergy in thermodynamics courses. Yet, in
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general, room exists for improvement in the area of exergy coverage in thermodynamics education, and efforts should be made to achieve these improvements. Three points related to improving thermodynamics education through better coverage of exergy are addressed in the following three subsections.
25.4.2 The Need for Exergy Literacy in Scientists and Engineers We need to ensure that our education systems provide all students who study thermodynamics with a good grounding in exergy. For exergy methods to become more widely used and beneficially exploited, those who study and work in technical fieldsdparticularly where thermodynamics is applieddshould have a basic understanding of exergy. In addition, technical managers and decision makers require at least an appreciation of what exergy is and how it is used, if they are to make proper decisions on matters where exergy is, or should be, considered. Some may suggest that we do not, for practical purposes, need such an understanding of exergy among technical personnel. Some examples help refute such suggestions: l
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Research proposals have at times not been funded, in large part because exergy methods formed part of the approach. On reading the comments of reviewers of such proposals, it is sometimes evident that the reviewers have read energy in place of exergy throughout the proposalsdrendering them utterly meaningless. This result can occur despite the fact that great pains are often taken within proposals to emphasize the need to use exergy methods. What perhaps remains most disconcerting is that, in many of these instances, the reviewers have technical backgrounds. Government officials or company managers have admitted to exergy researchers and practitioners that, in many instances, they chose not to use exergy on a project or activity, not because an exergy approach was unsuitable, but because they did not understand it or had never heard of it. This situation is problematic because decision making, when it is based on avoiding topics about which one is ignorant, cannot be productive.
We consequently feel in general that a strong need exists to improve the “exergy literacy” of engineers and scientists.
25.4.3 Understanding the Second Law through Exergy The Second Law of Thermodynamics (SLT) often makes students of thermodynamics fearful. Introducing the concept of entropy usually only increases their trepidation. Even students who pass courses on thermodynamics and ultimately
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graduate often retain fears of the SLT and entropy and feel they do not really understand these topics. Ahrendts (1980), for example, begins one of his articles on exergy methods with “Thermodynamics is not a very popular science, because the concepts in thermodynamics do not conform to the unsophisticated human experience.” Focusing on the SLT he continues “Traditional formulations of the Second Law prevent a simple understanding of energy conversions, because the application of the entropy concept to those processes is often looked upon as a miracle.” Others also have agreed with these concerns and developed different approaches to teaching the SLT. One example is a thermodynamics text by Dixon (1975), the preface of which states “entropy is [not] the most significant or useful aspect of the Second Law” and “the Second Law has to do with the concept of degradation of energy; that is, with loss of useful work potential.” Dixon introduces the SLT through the concept of degradation of energy, claiming “degradation . because it is a work term, is an easily grasped concept.” By focusing on degradation of energy rather than the abstract property entropy, Dixon feels his book results in “a clearer physical meaning for entropy.” This approach, although instructive for some, is still somewhat abstract and vague. The approach comes close to teaching the SLT through exergy, and would likely be clearer if it did so. Exergy provides a perspective of the SLT and entropy that is much more intuitively understandable to students. The definition of exergy, which states that exergy is the maximum work that can be obtained from a system or flow within a reference environment, is usually much more straightforward than the definition of entropy. Also, characteristics of exergydsuch as it being a nonconserved quantitydare normally easier for students to grasp than the concepts surrounding entropy and its characteristics. Thus, we feel that exergy should generally form a central component of thermodynamics courses. More specifically, exergy should play a significant role in dealing with and teaching the SLT. Such an approach would likely make the SLT more understandable and practical and less fear inspiring. Some readers will point out correctly that there exist some additional complexities when dealing with exergy rather than entropy (e.g., a reference environment must be introduced and defined). Nevertheless, we believe that the overall benefits of approaching the SLT through exergy outweigh the difficulties.
graduate level. In the latter case, the rationale often provided is that students need a firm grounding in traditional thermodynamics before they deal with exergy. Those who support including exergy as a part of the undergraduate curriculum, on the other hand, claim this approach is necessary because exergy forms a critical and important part of basic thermodynamics. Further support for this argument is added by earlier statements in this article about exergy providing a preferable approach to dealing with and teaching the SLT. Although there is likely some merit in each of the rationales for different placements of exergy in curricula, this author nevertheless believes that some coverage of exergy should be required in all undergraduate courses in engineering thermodynamics. Beyond such a core of exergy material, however, there are multiple ways in which additional exergy material can be incorporated into engineering curricula at undergraduate or graduate levels. Exergy methods can also be incorporated into courses that apply to thermodynamics. In Thermal Design and Optimization, for instance, Bejan et al. (1996) feature a substantial amount of material on exergy and related methods. They explain in the preface that they include exergy in the text “because an increasing number of engineers and engineering managers worldwide agree that it has considerable merit and are advocating its use.” They state further that their aim in featuring exergy and related methods is “to contribute to the education of the next generation of thermal system designers and to the background of currently active designers who feel the need for more effective design methods.” These authors clearly regard exergy as a critical component in thermal design education, whose importance will only increase in the future. Much room for debate exists about the place for exergy in a curriculum. Perhaps no single answer exists, and each approach will retain its proponents. Some engineering thermodynamics curricula, to their detriment, do not cover exergy at all, but these are likely in the minority. The range of views on how exergy can and should be incorporated into a thermodynamics curriculum is sufficiently diverse that a consensus on the best approach is almost certainly not possible in the near term. It is even questionable whether a consensus can be reached in the long term, after exergy methods mature. Two points help illustrate this view:
25.4.4 Exergy’s Place in a Curriculum
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A challenging issue is where exergy should be covered in a curriculum. In engineering programs, for example, exergy is sometimes covered lightly in thermodynamics courses at the undergraduate level. Sometimes exergy is covered separately, as either a core or an elective undergraduate course, while in some schools exergy is only covered at the
A panel session on The Second Law in Engineering Education was held within the Symposium on Thermodynamics and the Design, Analysis, and Improvement of Energy Systems, at the 1996 International Mechanical Engineering Congress and Exposition of the American Society of Mechanical Engineers (El-Sayed et al., 1997). Among the topics covered were whether or not undergraduate engineers need to be educated in the SLT
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and how much depth is required in this area. The panelists included representatives of academia and industry, as well as respected thermodynamicists and exergy proponents. Although several opinions were expressed on the need to include exergy methods in the teaching of the SLT, the views expressed varied greatlydemphasizing the difficulties in reaching a consensus on the best approach for incorporating exergy into a thermodynamics curriculum. Consideration of the nomenclature and terminology of exergy analysis reveals that a diversity of names and symbols presently exist for the same quantities in exergy analysis. This situation persists despite efforts to reach a common nomenclature and terminology. This weakness demonstrates how difficult it is to reach a consensus just on the relatively narrow topic of nomenclature and terminology, not to mention reaching a consensus on the broader topic of incorporating exergy into a thermodynamics curriculum.
25.5 CLOSING REMARKS The key elements of this chapter are awareness, understanding, and education as they relate to exergy and its role in policy making. The relation between these key elements is illustrated in Figure 25.3. There, it is shown that an understanding and awareness of exergy requires, for all people, education. The types of education that are appropriate for
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technical persons such as engineers and scientists are shown to be different from those that are appropriate for nontechnical persons such as members of the public, government, or media. But, in a general sense, the factors involved in raising awareness and understanding are similar conceptually, and differ mainly in depth and rigor of treatment. The arguments presented in this chapter demonstrate that the public is often confused when discussing energy and a need exists to improve public understanding and awareness of exergy. Such understanding and awareness is essential if we are to better address the energy issues and problems of today and tomorrow. Thus, exergy can play a key role in developing appropriate and beneficial energyrelated policies, but exploiting the potential of exergy requires appropriate support for public education and awareness about exergy. In support of the need for public understanding and awareness of exergy, it should take on a prominent place in thermodynamics courses. Beyond elucidating the concepts of the SLT and entropy, such an approach can help ensure a rudimentary understanding of exergy in all technical personnel. An approach based on exergy could make the SLT more interesting, appealing, and practical, as well as less daunting and confusing. Then, it may be easier to improve general understanding of exergy in the scientific and engineering communities, as well as the general public, by ensuring that a basic level of “exergy literacy” exists among engineers and scientistsdparticularly those involved in decision making. Education policies that support
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FIGURE 25.3 Illustration of the importance of education in building awareness and understanding of exergy among different categories of people.
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inclusion of exergy in relevant curricula, at all appropriate education levels, should be considered.
PROBLEMS 25.1 Conduct research to determine if thermodynamics textbooks written several decades ago cover exergy and to what extent. 25.2 Almost all present undergraduate thermodynamics textbooks have at least one chapter devoted to exergy. If you were the instructor of a single thermodynamics course and you could only cover some of the chapters, would you cover exergy? Provide reasons for your answer.
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25.3 Do you favor changing the way thermodynamics is taught by adopting an exergy-based approach? Why? 25.4 Explain how a better understanding of exergy by engineering students can help improve public awareness of exergy. 25.5 Explain how exergy is a useful tool in policy making related to energy. Provide examples. 25.6 Is it realistic to expect that the level of understanding of the public about exergy should be comparable to that for energy? Explain. 25.7 Explain how a better understanding and appreciation of exergy by the public and by policy makers can help foster more efficient use of energy sources and minimize their effects on environment.