Ejectors for Efficient Refrigeration PDF
Preview Ejectors for Efficient Refrigeration
Giuseppe Grazzini · Adriano Milazzo Federico Mazzelli Ejectors for Effi cient Refrigeration Design, Applications and Computational Fluid Dynamics fi Ejectors for Ef cient Refrigeration Giuseppe Grazzini (cid:129) Adriano Milazzo (cid:129) Federico Mazzelli fi Ejectors for Ef cient Refrigeration Design, Applications and Computational Fluid Dynamics GiuseppeGrazzini AdrianoMilazzo DepartmentofIndustrialEngineering DepartmentofIndustrialEngineering UniversityofFlorence UniversityofFlorence Florence,Italy Florence,Italy FedericoMazzelli DepartmentofIndustrialEngineering UniversityofFlorence Florence,Italy ISBN978-3-319-75243-3 ISBN978-3-319-75244-0 (eBook) https://doi.org/10.1007/978-3-319-75244-0 LibraryofCongressControlNumber:2018933589 ©SpringerInternationalPublishingAG,partofSpringerNature2018 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartofthe materialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation, broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformation storageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodology nowknownorhereafterdeveloped. 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Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland “To our families” Preface: Past, Present, and Future of Ejector Refrigeration The history of ejector refrigeration is tightly nestled in the broader history of refrigeration.Whenthesteamjetchillerfirstappeared,manydifferentrefrigeration cycles had already been used for both refrigeration and air conditioning purposes. However,thesteamjetrefrigeratorhadtheadvantagethatitcouldrunusingexhaust steam from any source (steam engines, industrial or chemical processes, etc.). Therefore, starting in1910, steam jet refrigeration systems founduse inbreweries, chemicalfactories,theatres,ships,andtrains. Despite the promising start, the use of supersonic ejectors for refrigeration applicationsalmost endedwhen Thomas Midgley Jr. andhis associates introduced the first synthetic refrigerants during the 1930s. These gases could completely overcome the problems that hampered the large-scale commercialization of vapor compression systems. Meanwhile, steam plants became less common and electric energywasmadebroadlyavailableindevelopedcountries.Therefore,thesteamjet cycles were gradually replaced by more efficient vapor compression systems (although some east European countries such as Czechoslovakia and Russia manufacturedthesesystemsaslateas19601). Despite the scarce success in refrigeration applications, the research on super- sonicejectorsdidnotstop,giventheirwidespreaduseinmanyotherfields(aswillbe illustratedinChap.1).Duringthefirsthalfofthetwentiethcentury,hugetheoretical progressesweremadeintheunderstandingoftheprinciplesofaerodynamicsapplied tosupersonicflows.ThedevelopmentswerepioneeredbyscientistslikeErnstMach, Ludwig Prandtl and his dynasty of brilliant students: Theodore von Karman, TheodoreMeyer,Adolf Busemann,Hermann Schlichtingandmany others.Bythe end of the 1950s, Joseph H. Keenan and his colleagues at MIT had perfected the theory of mixing inside supersonic ejectors. Many design concepts have been developed since then, and systematic experimental activities have been performed tooptimizesystemdesign. 1Arora,C.P.,2003.RefrigerationandAirConditioning,Tata-McGraw-Hill. vii viii Preface:Past,Present,andFutureofEjectorRefrigeration TheoilcrisisthatfollowedtheYomKippurWarin1973andtheriseinawareness ofozonedepletionin 1974laidoutthegroundworkforarevivalofejectorsystems. These two events, in conjunction with the increase in refrigeration demand and the appearance of stringent regulations on ozone depletion and global warming (Montreal and Kyoto Protocol in 1987 and 1992, respectively), prompted research towardnew,economical,andenvironmentallysafetechnologies.Asaresult,ejector refrigerationexperiencedarenewedinterest,andagreatnumberofresearchcenters worldwidestartedstudiesinthisfield. In recent years, thermodynamic optimization has been extensively pursued on ejectorsandejectorchillers.Meanwhile,CFDhastakenaleadingroleintheanalysis oftheinternalflowswithinsupersonicejectors.Startingfromaglobalanalysisofthe ejector behavior in terms of entrainment ratio and pressure lift, CFD simulations havebeenspecializedonthestudyofcomplexinternalphenomena,suchasmixing andshocktrains.Thesenumericalresults arenowgenerating increasinglyaccurate results thanks to the appearance of new, sophisticated flow visualization studies. Meanwhile,alargenumberofconfigurationalternativestothestandardejectorcycle havebeenproposed,whichinclude“passive”systems,cycleswithmultipleparallel ejectors,multiplenozzles,annularnozzles,andsoforth. Yet, vapor compression and, to a lesser extent, absorption systems still completelydominatetherefrigerationmarket.Quitesurprisingly,theejectordesign from a macroscopic point of view seems relatively unchanged in the last decades. Innovative proposals, like the above-cited unconventional configurations or improveddesignprocedures,didn’timpactthefundamentalstructureoftheejector chilleraswouldhavebeenexpected.Industriesrelyontheirconsolidatedexperience andproceedwithunderstandablecautiononthepathofinnovation,whilethehuge amount of scientific literature produced seems somewhat distant from practical application. Todate,theuseofejectorstoenhancetheefficiencyofconventionalrefrigeration cycles seems to be the most promising development. Ejector expansion cycles are emerging as enabling technology for CO vapor compression cycles, as proven by 2 theincreasedinterestmanifestedbyleadingglobalplayersintherefrigerationarena (e.g.,DanfossorCarel).Otherrefrigerants(ammonia,hydrocarbons,orHFO)allow moderate losses in the expansion valve, and hence the insertion of additional components to increase the system efficiency could seem questionable. However, asthesizeincreases,evenagrowthinefficiencybelow10%maywellbeworthofa modest complication. In principle, the cost of a mass-produced ejector could be acceptable in comparison with other basic components of the refrigeration system. As will be shown in Sect. 1.3, the insertion of an ejector may be beneficial to the creation of an intermediate evaporation level or may allow liquid circulation in flooded evaporators. As soon as these new possibilities are fully pursued and the ejectoreffectivelyintegratedwithallotherfunctionswithintherefrigerationsystem (e.g.,regulationandcontrol),webelievethatthediffusionofejectorsforexpansion recovery will become widespread. Also, the integration of ejectors in absorption systems seem to produce significant results without requiring too heavy Preface:Past,Present,andFutureofEjectorRefrigeration ix modificationstothecycleevenif,totheauthor’sknowledge,therearenoattemptsof commercializationyet. The future of supersonic ejectors in heat-powered refrigeration cycles, on the other hand, seems to be somewhat more uncertain. Research conducted over the yearsatourdepartmentsuggeststhatejectorchillerscanbeeasilymanufacturedwith low-cost, off-the-shelf components (apart from the ejector itself, which must be tailored to the specific application under consideration). Unfortunately, the weak pointofthistypeofsystemisstillrepresentedbythelowthermodynamicefficiency. As an order of magnitude, one could set a target COP ¼ 0.7, which is currently reachedbycommerciallithiumbromideabsorptionchillers,butsignificantlyhigher thanthetypicalvaluesreportedforejectorchillersinthesameworkingconditions. Theuseofsolarenergytopowerejectorcyclesseemsalogicaloutcomebutmust becarefullyevaluated.Inarecentreview,KimandInfanteFerreira(2014)2makea comparison between solar thermal and solar electric cooling technologies, both in terms of thermodynamic performances and economic feasibility. The results show that,atpresent,thecheapestsolutionisrepresentedbythePVpanelscoupledwith commercial vapor compression chiller. This result is largely due to the recent dramaticdecreaseinPVcostandtothelarge production volumes thatmakevapor compressionchillersveryinexpensive. However, solar thermal collectors have also seen a significant decrease of their cost, mainly due to the large amount of collectors manufactured and installed in China. In particular, evacuated tube collectors, thanks to their reduced heat loss, performbetteratrelativelyhightemperaturesandhavereachedahighmarketshare. Thesecouldbeprofitablyadoptedtopowerheat-drivenrefrigerators. Wasteheatrecoverymayrepresentanotherfieldforsuccessfulapplication.Heat recoveryinindustries,combinedheating,powerandcooling,ordistrictheatingand coolingmayallpotentiallyprofitfromtheapplicationofejectorchillers.Whenever wasteheatisdirectlyavailableinformofwatervaporatmoderatetemperature,the steamejectorisundoubtedlythecheapestandsimplestoption. Anoverturnofthecurrentsupremacyofabsorptionchillersontheheat-powered refrigerationmarketisunlikelyandundesirable,butejectorrefrigerationcouldoffer aneffectivealternativeinallcaseswheresimplicity,reliability,andlowinvestment costs are required. From a practical point of view, the key parameter in any refrigerationsystemisthetotalcostperunitcoolingload.Iftheinputthermalenergy hasloworzerocost(e.g.,wasteheatorsolarpower),thecostofcoolingismainly relatedtotheinvestment,whichthereforeisthemainobjectivefunctiontominimize. Compared with lithium bromide/water absorption refrigerators, ejector cycles mayavoidproblemsofinternalcorrosionandcrystallizationofthesolution.Ammo- nia/waterabsorptionrefrigerators,ontheotherhand,useatoxicfluid,whileejector chillers may use nontoxic, nonflammable, and environmentally safe refrigerants 2Kim, D.S., Infante Ferriera, C.A., 2014. Solar refrigeration options—a state-of-the-art review. InternationalJournalofRefrigeration,31,3–15. x Preface:Past,Present,andFutureofEjectorRefrigeration (e.g., water). These advantages potentially offer significant savings in terms of capitalandlifecyclemaintenancecosts. Ejectorrefrigerationmayalsohaveachanceofplayingaroleinspecificmarkets like developing countries, where access to electric power is limited and technical expertiseforthemaintenanceandreparationofstandardcompressionandabsorption cyclesislacking.Otheropportunitiesmayhopefullyariseinthefuture. This book is an attempt to review ideas, techniques, results, and open issues, combininginformationfromtheopenliteratureandfromtheindustry.Itisintended as a bridge between the extensive collection of scientific papers appearing on the relevantjournals and thepractical handbooks that have beenpublished inthepast, extending also toward the information published by the manufacturers. As such, it should promote and stimulate the discussion between the different players in the refrigeration arena and the experts of ejectors, including those who come from completelydifferentfields. 23rdDecember2017,Florence,Italy GiuseppeGrazzini AdrianoMilazzo FedericoMazzelli Acknowledgments The authors wish to thank Prof. Ian Eames for all the passionate and fruitful discussions about ejectors that inspired us while writing this book. Another very good friend, Prof. Yann Bartosiewicz, has shared with us many interesting ideas. Prof. Srinivas Garimella and Adrienne B. Little have also inspired us with some originalproposals.Lastbutnotleast,Prof.KonstantinE.Aronsonandhiscoworkers Dmitry V. Brezgin and Ilia Murmanskii have been involved in our work and contributedwithoriginalideas. FrigelS.p.A.hassupportedustechnicallyandeconomicallythroughoutallthese years, and we are very grateful to Michele Livi, who has been responsible for the ejectorproject. Since2016,theauthorshaveparticipatedina“PRIN”researchproject(fundedby theItalianMinistryofUniversityandResearchforstrategicnationalprojects)named “CleanHeatingandCoolingTechnologiesforanEnergyEfficientSmartGrid”that groupseightItalianUniversitiesworkingonrefrigeration. Special thanks also go to those people who belong or have been part of our research group and involved in our research on ejectors: Andrea Rocchetti, Francesco Giacomelli, Furio Barbetti, Jafar Mahmoudian, Simone Salvadori, DarioPaganini,andSamuelePiazzini. xi
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