Table Of ContentGiuseppe 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
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“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
