Bahrain would like to express my thanks
Bahrain University College of Engineering Mechanical Engineering Department A Senior Design Project (MENG 490) Report Submitted in partial fulfillment of the requirements for the degree of B.Sc. in Mechanical Engineering Student name: Ali Abdulla Ali AlAradi 20132414 Supervisor: Professor Teoman Ayhan Program : Mechanical Engineering Starting Date: October19th, 2017 Submission Date: January 2nd, 2018 Acknowledgment I would like to express my thanks and appreciation my supervisor Prof. Teoman Ayhan for his continuous support and advice. Special thanks to my family and colleagues in the University of Bahrain, as well as every member of the university’s staff. This would have been impossible to do without them. Abstract This abstract is a very important and obligatory part of the report allowing the potential reader to judge, if he is the target of this report. The abstract is a summary of the entire report and not an introduction to the report. It should be written with broadly understandable technical language and should be self-contained, i.e. should not contain any references or citations. Also the usage of abbreviations and acronyms should be avoided, since the same acronyms or abbreviations can have different meanings on different research fields. The abstract should typically contain about 400 words and in any cases not more than one page. The definition of the research field and the most important outcome of the presented research are the obligatory components of the abstract. (Limited to Only one page) Contents Chapter 1 Introduction. 1 Chapter 2 Background. 3 2.1 History of Exergy. 3 2.2 Conventional Exergy Analysis History. 4 2.3 Advanced Exergy Analysis History. 5 Chapter 3 Design and Implementation. 6 3.1 General Mathematical Representation & Definition. 6 3.1.1 Conventional Exergy Analysis. 6 3.1.2 Advanced Exergy Analysis. 8 3.2 Case Study 1: Vapor Compression Refrigeration System.. 11 Chapter 4 Results and Discussion. 12 Chapter 5 Conclusion and Future Work. 13 References 14 Appendices 15 You can add Appendices here, if needed. Starting from Appendix A and so on. 15 Appendix A 16 Work schedule (Gantt Chart) 16 List of Figures Figure (1.1): The UOB Logo. 1 0 0 0 Figure (2.6): The Logo. 5 0 0 0 Figure (3.10): The Logo. 8 Listof Tables Table (1.1) The Data of…………… .. .. .. Table (2.4) Statistical Data ……… Acronyms B. Sc. Bachelor of Science List of Symbols Nj Number of channels for user j Chapter 1 Introduction The purpose of this report is to explain exergy and advanced exergy analysis and how they can be used to improve thermal systems. Explaining the difference between conventional exergy analysis and advanced exergy analysis is also necessary to understand the advantages that the advanced exergy analysis has over the conventional one, and if it is worth the extra time and effort to do the analysis. Exergy analysis is an important tool to evaluate and understand the efficiency and performance of any system, thermal or otherwise. Its currently the most wildly taught and used method to measure how much of the system’s true potential is being utilized, and how far it is possible to improve it before hitting the theoretical ceiling. The controversial exergy analysis methods do provide how much exergy is lost in the system and its efficiency, but it failsto provide much else. For practical application, we must understand where the losses occur, in the components of the system rather than the system as a whole. We must also understand how the current technological limitations prevent us from reaching that theoretical maximum performance. As such, to get a clearer look into what can be improved, how much it can be improved, and what would be the benefits of improving it, an alternative to the somewhat outdated controversial exergy analysis method must be used. This report discusses thealternative. Advanced exergy analysis. Advanced exergy analysis specializes in analyzing the exergy losses in the processes, known as the exergy destruction. It divides the exergy destruction into two separate parts depending on two different criteria’s. The exergy destruction is either divided into avoidable and unavoidable exergy destruction, or into endogenous and exogenous exergy destruction. The first criteria is self-explanatory. The avoidable exergy destruction can be eliminated by either improving the component or the system as a whole. The unavoidable exergy destruction cannot be avoided due to technological limitations. This criterion provides a simple method to understandjust how much the component can be improved, as well as the maximum possible performance after going through all the possibleimprovements. The second one is slightly less straightforward. The endogenous exergy destruction is the exergy destruction in a specific component while assuming the remaining components are all functioning ideally. The exogenous exergy destruction is the remaining exergy destruction, influenced by both the component’s own irreversibilities and flaws as well as the other components’ flaws. Using theendogenous exergy destruction, we can calculate how much we can improve the component by improving itself, without having to touch the remaining components at all. The idea behind advanced exergy analysis is not to use a single one of the aforementioned exergy destruction separations on its own, but rather to combine them both together in order to find the endogenous available, endogenous unavailable, exogenous available, and exogenous unavailable parts of the exergy destruction in each component. This report starts with background and historical information on the concepts and applications of exergy, conventional exergy analysis, and advanced exergy analysis, followed by explaining the methodology of performing the analysis, and finally concluded by two case studies showcasing the analysis in action. Chapter 2 Background In order to begin understanding either exergy analysis methods one must understand what exergy itself is. To put it in the simplest terms energy is divided into two parts, exergy and anergy. Exergy is the usable energy that can be utilized. Anergy, on the other hand, is the energy that cannot be used or utilized. While energy is preserved in the universe and cannot be destroyed or created, the same cannot be said about exergy. Exergy can be destroyed. In fact, with the exception of theoretical, ideal, reversible processes the second law of thermodynamics dictates that exergy must be destroyed. This brings forth the importance of exergy analysis. It would be unrealistic to expect any system to be an ideal reversible system, and as such, all systems would have a certain amount of exergy destruction. Performing exergy analysis would allow us to diagnose the system and find out which process has the most exergy destruction. Seeing that the loss of exergy is a flaw in all systems, we would naturally want to lower the exergy destruction of system, and conventional exergyanalysis allows us to priorities the processes and parts that have higher exergy destruction in order to improve them individually and lower the exergy destruction of the system. Although our current mathematical understanding of exergy dates back to at least the early 1870s and the first American engineering doctorate holder Dr. Josiah Willard Gibbs1, the term ‘exergy’ itself would not come to use until Zoran Rant derives it from Greek terminology in the middle 20th century 2. 2.1 History of Exergy The earliest and most basic concepts of exergy and second law of thermodynamics are traced back to the 1820s instead of the 1870s, and to a man by the name of Sadi Carnot 3. His work was almost exclusively theoretical, and involved no mathematics. This, alongside the fact that it was thought out in the time where caloric theory was more widely accepted than the kinetic theory in the study of thermodynamics, meant that despite Carnot’s brilliant concept,some of which like the Carnot Engine are still in use to this very day, his work would be ignored and unused for nearly half a century. Over four decades later, Dr. Gibbs would utilize Carnot’s concepts, alongside his own understanding of thermochemistry and research, to derive the mathematics of what is now known as exergy. 2.2 Conventional Exergy Analysis History While the basic definition and mathematical derivation of exergy was done in the 1870s, it would still take close to a century before worldwide acceptance and agreeance of Zoran Rants’ terminology 4. Even the most innovative of applications of the conventional exergy analysis did not occur until the late 1950s and early 1960s, by works of Keller on steam power cycles in 1959, and Fratzscher, Gašperši?, and Rant in 1961. Because the theoretical work was not completed and accepted until the end of the 1960s, only a few people were confident enough in this new methodology that was basically inits infancy enough to test it on practical applications, let alone use it on major systems and power plants. This all would come to change in the 1970s. Exergy and the second law of thermodynamics were widely accepted by the scientific and engineering community to the point where it was in textbooks and paved the way for engineering thermodynamics to become its own field. Coupled with the sudden need to maximize every oil fueled system’s efficiency that immerged due to the oil crisis of 1973, and the world had both motive and opportunity to embark into an age of scientific advancement in terms exergy analysis. The practical applications did start with the aforementioned works on steam power cycles, but they soon spread to cover over thermal systems such as gas turbine cycles starting with Chambadal’s work in 1965, the renewable energy cycles in the early 1980s by Edgerton and Bejan, heat exchangers by Elsner in 1960, Cryogenics by Martinowsky in 1950, and distillation by Freshwater in 1951. Works on exergy on topics other than thermal systems also pioneered the exergy study itself, most notably Rant’s work in 1947 and Denbigh’s in 1956 on chemical processes and systems rather than thermal ones. While conventional exergy analysis has found its place as an important tool for both economic and environmental evaluation and analysis of thermal andchemical systems, it is still a work in progress in other departments, and that is what conventional exergy analysis students and researchers focus on, as well as improving its accessibility for existing systems. Even today, four decades after the scientific community accepted the concepts exergy, it is still a field in need, and demand, of extensive research. 2.3 Advanced Exergy Analysis History Advanced Exergy Analysis is quite new and is unheard of even among fresh graduates of Mechanical Engineering. The term ‘advanced exergy analysis’ does not appear to have been used prior to 2009, and the earliest I have been able to track some of its methodology is to 2002 for the avoidable and unavoidable splitting 5 and 2006 for the endogenous and exogenous splitting 6. The avoidable and unavoidable exergy destruction splitting originates, in concept, from the economical avoidable and unavoidable cost analysis, but it does not function on the sameprinciples. In accounting and economics, the avoidable costs refer to costs that can be avoided by making specific choices, like spending less on advertising for a service or quality control on a product. In exergy analysis, it is done by comparing the minimum scientific theoreticalcost and the minimum technological applicable cost. To simplify, it compares between the lowest possible operation cost in the foreseeable future. Chapter 3 Design and Implementation 3.1 General Mathematical Representation & Definition 3.1.1 Conventional Exergy Analysis The energy in heat transfer can be divided into two parts: Where Q is the heat transfer, X is the exergy, and A is the anergy. Using the Carnot efficiency to calculate the theoretical exergy and anergy in the system: Where is the Carnot efficiency T0 is the ambient temperature T is the component temperature. The theoretical exergy and anergy are: Exergy can be mathematically represented by two equations, the first of which is: Where X2 – X1 is the change in exergy. is the change in internal energy. p0 is the pressure. is the change in volume T0 is the ambient temperature. is the change in entropy. is the change in kinetic energy. is the change in potential energy. Using the following equations: The same equation can be represented as the following when using specific internal energy, volume, kinetic andpotential energies, and entropies: Where is the velocity. g is the gravitational acceleration. z is the height. The following equation can be used to further simplify the exergy balance equation: To the following form: Where h is the specific enthalpy. The following equation can be used to define the specific exergy: Which would reduce the equation to: The second equation is: Where: Tc is the temperature of component that receives that heat transfer. Q is heat transfer into the system. W is the useful work out of the system. Xdes is the exergy destruction. By subtracting the two equations, we get the following equation: Both equations can be rearranged to be in term of the Exergy destruction, which is the variable we want to calculate from the exergy balance to be as such Alternatively, an entropy balance can be performed and after finding the entropy generation, the exergy destruction can be calculated using the following equation: Where is the entropy generation. The exergy balance equation is the following: Where Xin is the exergy entering the component, and Xout is the exergy leaving the component. 3.1.2 Advanced Exergy Analysis 22.214.171.124 Theoretical Systems Assuming we have a theoretical system where all the components are in series, and either the exergy output or input of the whole system is constant. Let the exergetic efficiency of each component be defined by: Where: n is the number of the component. Xin is the exergy entering the component. Xout is the exergy leaving the component. is the exergetic efficiency. Regardless of the case (Xin constant or Xout constant), the following equation would define the total unavoidable exergy destruction of the system: The exergy destruction and endogenous exergy destruction for each component: And And . . . And And The unavoidable exergy destruction for the system: Combining the unavoidable and endogenous exergy destruction rules to find the unavoidable endogenous exergy destruction: . . . Under either assumption, the results should be the same provided that the exergy input and output satisfy the following equation: 126.96.36.199 Real Systems 188.8.131.52.1 Endogenous and exogenous exergy destruction splitting In order to split the exergy to endogenous and exogenous exergy, we must establish theoretical cycles and several theoretical-real hybrid cycles. The concept of said theoretical cycles is simple: minimize the exergy destruction. It would change depending on the component, but the general rules are: If it is a component that can have the theoretical isentropic efficiency of 1 such as pumps and turbines: If the component is a heat exchanger or something similar: Which occurs when the difference in temperature is zero. After establishing the perfect, ideal, theoretical cycle, we calculate the endogenous exergy destruction of each component by putting the actual data of that specific component in the theoretical cycle, thus creating a hybrid cycle. 184.108.40.206.2 Avoidable and unavoidable exergy destruction splitting To find the unavoidable exergy destruction we must use a simulation to find how the processes in the component would function under near-ideal conditions that cannot be achieved in the foreseeable future. Said simulation will give us the value of We then use that value to calculate the unavoidable exergy destruction using the following equation: Where is the actual exergy leaving the component/process. 220.127.116.11.3 Combining the two splittings The method to do this one is rather straightforward, once we actually do the previous two splitting methods. Using the same data we obtained from the previous splitting methods, we use the following equation to get the unavoidable endogenous exergy destruction: Once the unavoidable endogenous exergy destruction is calculated, the remaining information, namely the avoidable endogenous, unavoidable exogenous, and avoidable exogenous exergy destruction can be calculated using the following equations: 3.2 Case Study 1: Vapor Compression Refrigeration System The following data were measured from a Vapor Compression Refrigeration System that uses refrigerant R12 and a water supply to cool air. Figure 1 Simple Vapor Compression Refrigeration System Table 1 Vapor Compressor Readings Reading Units Value Refrigerant Data R-12 Mass flow rate kg/s 6.5×10-3 Evaporator Pressure (state 4) KPa 362 Condenser pressure (state 2) KPa 700 Compressor inlet temperature (state 1) oC 5 Condenser inlet temperature (state 2) oC 68 Expansion valve inlet temperature (state 3) oC 28* Evaporator inlet temperature (state 4) oC 5 Water Data Water Flow Rate kg/s 50×10-3 Condenser inlet temperature (state 5) oC 21 Condenser outlet temperature (state 6) oC 23 Air Data Air Flow Rate kg/s 0.1 Evaporator inlet temperature (state 7) oC 20 Evaporator outlet temperature (state 8) oC 12 Surroundings Data Surrounding Temperature (T0) oC 21 Surrounding Pressure (P0) KPa 100 3.2.1 Conventional exergy analysis for each component The majority of the calculations were done by EES. The EES code is available in the appendix. The following steps were performed: 1) Using EES’ database, the specific enthalpy, specific entropy, and specific exergy were obtained for each state. 2) Using the following equation, the work done by the compressor was calculated: 3) The exergy destruction in each component was calculated using the following equations 4) The input exergy is found using the following equations: 5) The exergy output is found using the following equations 3.2.2 Advanced Exergy Analysis 18.104.22.168 Endogenous and exogenous exergy destruction Splitting To perform this splitting, a theoretical cycle is created. In the theoretical cycle, the following conditions are given to minimize or eliminate exergy destruction in each component, as well as the cycle. 1) Heat Exchangers (Evaporator and Condenser): 2) Condenser: 3) Evaporator: 4) Compressor: Entropic efficiency = 100%. Exergy destruction = 0. 5) Expansion valve is replaced with an ideal expansion process, which does not occur naturally. As such, Exergy destruction in the expansion valve is taken to be equal to zero. The follow Chapter 4 Results and Discussion After the presenting your design and work, the results obtained are shown and discussed in this chapter. How do you kneo that your design workded and that the problem you started out to solve has actually been solved. If not solved, then you need to discuss the reasons and propose solutions . Chapter 5 Conclusion and Future Work Write your conclusions here. Typically 1-2 paragraphs where you tell what the problem was and how it was solve. Then the main results in 1-2 paragraphs or possibly as a list. In addition, you can describe topics for future research in the last paragraph. References 1 J.W. Gibbs (1873). “A method of geometrical representation of thermodynamic properties of substances by means of surfaces: reprinted in Gibbs, Collected Works, ed. W. R. Longley and R. G. Van Name (New York: Longmans, Green, 1931)”. Transactions of the Connecticut Academy of Arts and Sciences. 2: 382–404. 2 David Sanborn Scott (2008). Smelling Land: The Hydrogen Defense Against Climate Catastrophe. Queen’s Printer Publishing. p. 206. ISBN 978-0-9809674-0-1. 3 S. Carnot (1824). Réflexions sur la puissance motrice du feu sur les machines propres a developper cette puissance. (Reflections on the Motive Power of Fire and on Machines Fitted to Develop That Power. Translated and edited by R.H. Thurston 1890). Paris: Bachelier. 4 Enrico Sciubba (2007), A brief Commented History of Exergy From the Beginnings to 2004. Int. J. of Thermodynamics ISSN 1301-9724 Vol. 10 (No. 1), pp. 1-26, March 2007. 5 George Tsatsaronis & Moung-Ho Parka (2002), On avoidable and unavoidable exergy destructions and investment costs in thermal systems, Energy Conversion and Management, Volume 43, Issues 9–12, June–August 2002, Pages 1259-1270 6 George Tsatsaronis, Solange O. Kelly and Tatiana V. Morosuk (2006) ASME 2006 International Mechanical Engineering Congress and Exposition, Advanced Energy Systems. Chicago, Illinois, USA, November 5 – 10, 2006, Conference Sponsors: Advanced Energy Systems Division, ISBN: 0-7918-4764-0 | eISBN: 0-7918-3790-4 .. .. ..