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Bahrain UniversityCollege of EngineeringMechanical Engineering Department Advanced Exergy Analysis for Thermal Systems A Senior Design Project (MENG 490) Report Submitted in partial fulfillment of therequirements 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 liketo express my thanks and appreciation my supervisor Prof. Teoman Ayhan for hiscontinuous support and advice.Special thanks to my family and colleagues in theUniversity of Bahrain, as well as every member of the university’s staff.
Thiswould have been impossible to do without them. AbstractThis abstract is avery important and obligatory part of the report allowing the potential readerto judge, if he is the target of this report. The abstract is a summary of theentire report and not an introduction to the report. It should be written withbroadly understandable technical language and should be self-contained, i.e.should not contain any references or citations. Also the usage of abbreviationsand acronyms should be avoided, since the same acronyms or abbreviations canhave different meanings on different research fields. The abstract shouldtypically contain about 400 words and in any cases not more than one page.
Thedefinition of the research field and the most important outcome of thepresented research are the obligatory components of the abstract.(Limited to Only one page)ContentsChapter1 Introduction. 1Chapter 2 Background. 32.1 Historyof Exergy. 32.
2 ConventionalExergy Analysis History. 42.3 AdvancedExergy Analysis History. 5Chapter 3 Design and Implementation. 63.1 GeneralMathematical Representation & Definition.
63.1.1 ConventionalExergy Analysis. 63.1.2 AdvancedExergy Analysis. 83.
2 CaseStudy 1: Vapor Compression Refrigeration System.. 11Chapter 4 Results and Discussion. 12Chapter 5 Conclusion and Future Work. 13References 14Appendices 15You can add Appendices here, if needed.
Starting from Appendix A and so on. 15Appendix A 16Work schedule (Gantt Chart) 16List of FiguresFigure (1.1): The UOB Logo. 1000Figure (2.6): The Logo. 5000Figure (3.
10): The Logo. 8 List of TablesTable (1.1) TheData of……………….
..Table (2.4) Statistical Data ……… Acronyms B. Sc. Bachelor of Science List of Symbols Nj Number of channels for user j Chapter 1 IntroductionThe purpose of this report is toexplain exergy and advanced exergy analysis and how they can be used to improvethermal systems.
Explaining the difference between conventional exergy analysisand advanced exergy analysis is also necessary to understand the advantagesthat the advanced exergy analysis has over the conventional one, and if it isworth the extra time and effort to do the analysis. Exergy analysis is an importanttool to evaluate and understand the efficiency and performance of any system,thermal or otherwise. Its currently the most wildly taught and used method tomeasure how much of the system’s true potential is being utilized, and how farit is possible to improve it before hitting the theoretical ceiling. Thecontroversial exergy analysis methods do provide the theoretical maximumperformance and how much exergy is lost in the system, but it fails to providemuch else. For practical application, we must understand where the lossesoccur, in the components of the system rather than the system as a whole. Wemust also understand how the physical and scientific limitations affect howclose we can get to that theoretical maximum performance. As such, to get aclearer look into what can be improved, how much it can be improved, and whatwould be the benefits of improving it, an alternative to the controversialexergy analysis method must be used. This report discusses the alternative.
Advanced exergy analysis.Advanced exergy analysisspecializes in analyzing the exergy losses in the processes, known as theexergy destruction. It divides the exergy destruction into two separate partsdepending on two different criteria’s. The exergy destruction is either dividedinto avoidable and unavoidable exergy destruction, or into endogenous andexogenous exergy destruction.The first criteria isself-explanatory. The avoidable exergy destruction can be eliminated by eitherimproving the component or the system as a whole.
The unavoidable exergydestruction cannot be avoided due to technological limitations. This criterionprovides a simple method to understand just how much the component can beimproved, as well as the maximum possible performance after going through allthe possible improvements.The second one is slightly lessstraightforward. The endogenous exergy destruction is the exergy destruction ina specific component while assuming the remaining components are all functioningideally. The exogenous exergy destruction is the remaining exergy destruction,influenced by both the component’s own irreversibilities and flaws as well asthe other components’ flaws.
Using the endogenous exergy destruction, we cancalculate how much we can improve the component by improving itself, withouthaving to touch the remaining components at all.The idea behind advanced exergyanalysis is not to use a single one of the aforementioned exergy destructionseparations on its own, but rather to combine them both together in order tofind the endogenous available, endogenous unavailable, exogenous available, andexogenous unavailable parts of the exergy destruction in each component.This report starts with backgroundand historical information on the concepts and applications of exergy,conventional exergy analysis, and advanced exergy analysis, followed byexplaining the methodology of performing the analysis, and finally concluded bytwo case studies showcasing the analysis in action. Chapter 2 BackgroundIn order to begin understandingeither exergy analysis methods one must understand what exergy itself is. Toput it in the simplest terms energy is divided into two parts, exergy andanergy.
Exergy is the usable energy that can be utilized. Anergy, on the otherhand, is the energy that cannot be used or utilized. While energy is preservedin the universe and cannot be destroyed or created, the same cannot be saidabout exergy. Exergy can be destroyed. In fact, with the exception oftheoretical, ideal, reversible processes the second law of thermodynamicsdictates that exergy must be destroyed. This brings forth the importance ofexergy analysis. It would be unrealistic to expect any system to be an idealreversible system, and as such, all systems would have a certain amount ofexergy destruction. Performing exergy analysis would allow us to diagnose thesystem and find out which process has the most exergy destruction.
Seeing thatthe loss of exergy is a flaw in all systems, we would naturally want to lowerthe exergy destruction of system, and conventional exergy analysis allows us topriorities the processes and parts that have higher exergy destruction in orderto improve them individually and lower the exergy destruction of the system.While our current mathematicalunderstanding of exergy dates back to at least the early 1870s and the firstAmerican engineering doctorate holder Dr. Josiah Willard Gibbs1, the term’exergy’ itself would not come to use until Zoran Rant derives it from Greekterminology in the middle 20th century 2. 2.1 History of ExergyThe earliest and most basicconcepts of exergy and second law of thermodynamics are traced back to the1820s instead of the 1870s, and to a man by the name of Sadi Carnot 3. Hiswork was almost exclusively theoretical, and involved no mathematics.
This,alongside the fact that it was thought out in the time where caloric theory wasmore widely accepted than the kinetic theory in the study of thermodynamics,meant that despite Carnot’s brilliant concept, some of which like the CarnotEngine are still in use to this very day, his work would be ignored and unusedfor nearly half a century.Over four decades later, Dr. Gibbswould utilize Carnot’s concepts, alongside his own understanding ofthermochemistry and research, to derive the mathematics of what is now known asexergy. 2.2 Conventional Exergy Analysis HistoryWhile the basic definition andmathematical derivation of exergy was done in the 1870s, it would still takeclose to a century before worldwide acceptance and agreeance of Zoran Rants’terminology 4. Even the mostinnovative of applications of the conventional exergy analysis did not occuruntil the late 1950s and early 1960s, by works of Keller on steam power cyclesin 1959, and Fratzscher, Gašperši?, and Rant in 1961. Because the theoreticalwork was not completed and accepted until the end of the 1960s, only a fewpeople were confident enough in this new methodology that was basically in itsinfancy enough to test it on practical applications, let alone use it on majorsystems and power plants.This all would come to change inthe 1970s.
Exergy and the second law of thermodynamics were widely accepted bythe scientific and engineering community to the point where it was in textbooksand paved the way for engineering thermodynamics to become its own field.Coupled with the sudden need to maximize every oil fueled system’s efficiencythat immerged due to the oil crisis of 1973, and the world had both motive andopportunity to embark into an age of scientific advancement in terms exergyanalysis. The practical applications didstart with the aforementioned works on steam power cycles, but they soon spreadto cover over thermal systems such as gas turbine cycles starting withChambadal’s work in 1965, the renewable energy cycles in the early 1980s byEdgerton and Bejan, heat exchangers by Elsner in 1960, Cryogenics byMartinowsky in 1950, and distillation by Freshwater in 1951. Works on exergy ontopics other than thermal systems also pioneered the exergy study itself, mostnotably Rant’s work in 1947 and Denbigh’s in 1956 on chemical processes andsystems rather than thermal ones. While conventional exergy analysishas found its place as an important tool for both economic and environmentalevaluation and analysis of thermal and chemical systems, it is still a work inprogress in other departments, and that is what conventional exergy analysisstudents and researchers focus on, as well as improving its accessibility forexisting systems. Even today, four decades after the scientific communityaccepted the concepts exergy, it is still a field in need, and demand, ofextensive research.2.3 Advanced Exergy Analysis History Advanced Exergy Analysis is quite new and is unheard of evenamong fresh graduates of Mechanical Engineering.
The term ‘advanced exergyanalysis’ does not appear to have been used prior to 2009, and the earliest Ihave been able to track some of its methodology is to 2002 for the avoidableand unavoidable splitting 5 and 2006 for the endogenous and exogenoussplitting 6. The avoidable and unavoidable exergy destruction splittingoriginates, in concept, from the economical avoidable and unavoidable costanalysis, but it does not function on the same principles. In accounting andeconomics, the avoidable costs refer to costs that can be avoided by makingspecific choices, like spending less on advertising for a service or qualitycontrol on a product. In exergy analysis, it is done by comparing the minimumscientific theoretical cost and the minimum technological applicable cost.
Toput it simply, it compares between the lowest possible operation cost in theforeseeable future. Chapter 3 Design and Implementation3.1 General Mathematical Representation &Definition3.1.1 Conventional Exergy AnalysisThe energy in heat transfer can be divided into two parts: Where Q is the heat transfer, X is the exergy, and A is theanergy.
Using the Carnot efficiency to calculate the theoreticalexergy and anergy in the system: Where is the CarnotefficiencyT0 is the ambient temperatureT is the component temperature.The theoretical exergy and anergy are: Exergy can be mathematically represented by two equations,the first of which is: WhereX2 – X1 is the change in exergy. is the change in internal energy.p0 is the pressure.
is the changein volumeT0 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 whenusing specific internal energy, volume, kinetic and potential energies, andentropies: Where is thevelocity.g is the gravitational acceleration.z is the height.The following equation can be used to further simplify theexergy balance equation: To the following form: Where h is the specific enthalpy.
The following equation can be used to define the specificexergy: Which would reduce the equation to: The second equation is: Where:Tc is the temperature of component that receivesthat 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 Exergydestruction, which is the variable we want to calculate from the exergy balanceto be as such Alternatively, an entropy balance can be performed and afterfinding the entropy generation, the exergy destruction can be calculated usingthe following equation: Where is theentropy 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 3.1.2.
1 TheoreticalSystemsAssuming we have a theoretical system where all thecomponents are in series, and either the exergy output or input of the wholesystem is constant.Let the exergetic efficiency of each component be definedby: Where:n is the number of the component.Xin is the exergy entering the component.Xout is the exergy leaving the component. is theexergetic efficiency.Regardless of the case (Xin constant or Xoutconstant), the following equation would define the total unavoidable exergy destructionof the system: The exergy destruction and endogenous exergy destruction foreach component: And And ..
. And And The unavoidable exergy destruction for the system: Combining the unavoidable and endogenousexergy destruction rules to find the unavoidable endogenous exergy destruction: … Under either assumption, the results should be the same providedthat the exergy input and output satisfy the following equation: 3.1.
2.1 Endogenousand exogenous exergy destruction splittingIn order to split the exergy to endogenous and exogenousexergy, we must establish theoretical cycles and hybrid. The concept of saidtheoretical cycles is simple: minimize the exergy destruction. It would changedepending on the component, but the general rules are:If it is a component that can have the theoreticalisentropic efficiency of 1 such as pumps and turbines: Ifthe component is a heat exchanger or something similar: Which occurs when the difference in temperature is zero.After establishing the perfect, ideal, theoretical cycle, wecalculate the endogenous exergy destruction of each component by puttingthe actual data of that specific component in the theoretical cycle, thuscreating the hybrid cycle.
22.214.171.124.2 Avoidableand unavoidable exergy destruction splittingTo find the unavoidable exergy destruction we must use asimulation to find how the processes in the component would function undernear-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 exergydestruction using the following equation: Where isthe actual exergy leaving the component/process.3.1.
2.2.3 Combiningthe two splittingsThe method to do this one is rather straightforward, once weactually do the previous two splitting methods.
Using the same data we obtainedfrom the previous splitting methods, we use the following equation to get theunavoidable endogenous exergy destruction: Once the unavoidable endogenous exergy destruction iscalculated, the remaining information, namely the avoidable endogenous,unavoidable exogenous, and avoidable exogenous exergy destruction can becalculated using the following equations: 3.2 Case Study 1: Vapor Compression RefrigerationSystemThefollowing data were measured from a Vapor Compression Refrigeration System thatuses 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 componentThe majority of the calculations were done by EES. The EEScode is available in the appendix.Thefollowing steps were performed:1) UsingEES’ database, the specific enthalpy, specific entropy, and specific exergywere obtained for each state.2) Usingthe following equation, the work done by the compressor was calculated: 3) Theexergy destruction in each component was calculated using the followingequations 4) Theinput exergy is found using the following equations: 5) Theexergy output is found using the following equations 3.2.2 Advanced Exergy Analysis3.2.2.
1 Endogenousand exogenous exergy destruction SplittingTo perform this splitting, a theoretical cycle is created.In the theoretical cycle, the following conditions are given to minimize oreliminate exergy destruction in each component, as well as the cycle. 1) HeatExchangers (Evaporator and Condenser): 2) Condenser: 3) Evaporator: 4) Compressor:Entropic efficiency = 100%. Exergy destruction = 0.5) Expansionvalve is replaced with an ideal expansion process, which does not occurnaturally. As such, Exergy destruction in the expansion valve is taken to beequal to zero. The followChapter 4 Results and DiscussionAfter the presentingyour design and work, the results obtained are shown and discussed in thischapter.
How do you kneo that your design workded and that the problem youstarted out to solve has actually been solved. If not solved, then you need todiscuss the reasons and propose solutions . Chapter 5 Conclusionand Future WorkWrite your conclusions here. Typically 1-2paragraphs where you tell what the problem was and how it was solve. Then themain results in 1-2 paragraphs or possibly as a list. In addition, you candescribe topics for future research in the last paragraph. References1 J.W.
Gibbs(1873). “A method of geometrical representation of thermodynamicproperties of substances by means of surfaces: reprinted in Gibbs, CollectedWorks, ed. W. R. Longley and R. G. Van Name (New York: Longmans, Green,1931)”. Transactions of the Connecticut Academy of Arts and Sciences.
2:382–404.2David Sanborn Scott (2008). Smelling Land: The Hydrogen Defense Against ClimateCatastrophe. Queen’s Printer Publishing. p.
206. ISBN 978-0-9809674-0-1.3 S. Carnot (1824). Réflexions sur la puissance motricedu feu sur les machines propres a developper cette puissance. (Reflections onthe 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 briefCommented History of Exergy From the Beginnings to 2004. Int. J.
ofThermodynamics ISSN 1301-9724 Vol. 10 (No. 1), pp. 1-26, March 2007.5 George Tsatsaronis & Moung-Ho Parka (2002), Onavoidable and unavoidable exergy destructions and investment costs in thermalsystems, Energy Conversion and Management, Volume 43, Issues 9–12, June–August2002, Pages 1259-12706 George Tsatsaronis, Solange O. Kelly and Tatiana V.
Morosuk (2006) ASME 2006 International Mechanical Engineering Congress andExposition, 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….
.. AppendicesYou can addAppendices here, if needed. Startingfrom Appendix A and so on.