外文翻譯--混合狀況和模型試驗(yàn).doc

MixingcasesandmodelexperimentsFoodorbiologicalmacromolecules,unlikechemicalpolymer,mostcomponentsincludingcarbohydrates,esters,fiberandwater.Inprinciple,eachtypeoffoodmaterialsisauniqueproductanditsviscosity.Thismeansmixoffoodingredientsfullyisdifficulttodesignitalsomeansthateverysuccessfuldesignisonekindoftailormadeproductsormodels.InexperimentalmethodinthepasttenyearshavesolvedmanyparticlesforT.S.EandS.S.Efoodingredients.Thesespecificinstancesofmixedtellsusthatimprovemixingcancreateabetterandmorehomogeneousproducts.Thisisresearchdiefastmixingelementsimpactonthemodelexperimenttoexplorehowtobetterunderstandtheirabilitytomix.3.1.Caseofsucrose-crystalmelting(s.s.e.)Traditionalcandyindustrialwateratpre-settemperaturedissolvedsucrosecrystalparticles6.Themeltinthemoldcostalotoftimeandenergyinthedehydration.Sugarinthiscasethewaterinthebasediffusionrateisverylow,soveryslowevaporation.Itwillalsoattractwedevelopedanewevaporationmethodtomakethemoisturecontentofrawmaterialsdowntoclosetothefinalproduct,forthisprocesstodesignanewscrewmixingextruder27.InthiscasethemosteconomicalS.S.Eextruderdesignisoutofthefeedingofsucrosecrystalparticlesbeyondthedesignschemeofanyexcesswater.3.1.1.ExperimentalUsedformeltingdrysugarsolidparticlesofdoublescrewextrusionmachinefoundationdesign,thisdesigncancompletemeltingknownoscatteredcrystals.Battenfeldsingle-screwextruder(D=50*103m,L/D=12,wallthickness=4mm,thescrewcompressionratio=3,speed=80)ofsucrosesolidsspraydrying,amixtureofsucroseandglucoseparticles(1:1)todealwithbothcopperandcobaltthermocouplemeasuringtemperaturedistribution,thedistributionisakindofmicrocosmicevaluation,usingdistancemeasuringinputpower,accordingtotheinternationalcamelvaluecomparisonmethodmeasuringthequalityandpercolor。3.1.2.ResultsanddiscussionPhenomenon,thelimitationsofthesucrosecrystalmeltingduringwhichexistsinthetwo-thirdsofspirallevel,sucrosecrystalshavenotmixedwithotherthingshere,thiskindofphenomenonineachuninterruptedhaveexistedinthesinglescrewextruder,heattransferofcylinderispoorer,therefore,thatmeanstime-consumingmeltingprocesscannotbemixedelementallocationinmaterialextrusioninthechoice,inthiscasetheso-calledextrusiondieheadprovidesasolution.So-calledthemixedfunctionofextrusiondieheadisdistributionofflow,andtheremainingsolidcrystalsscatteredinthethermalboundarylayeronthesurfaceofthecylinderbody,solidcrystalwillslowlymeltinthermalboundarylayer.Nowrealizealotofscatteredmeltisachievable,buttheL/Dratioisincreasedfrom12to16,eveniftheemergenceofthemeltwillpreventextrusionmachinespushinthematerials.S.S.E.throughputisplacedinacarefullycraftedsolidfeedareadecidedto7,thisdesignletfeedonlybythroughtheclearanceofscrewandbarrel.Figure7showsthestepbystepdevelopmentofworkfromstarttoendtotheprocessofmeltingandmelttemperaturedistributionmeasurement.3.2.Caseofbreakfastcerealproduction(counter-rotatingt.s.e.)Usedintheproductionofbreakfastcereals,rotateT.S.E.isaveryattractiveapieceofequipmentthatworkinsuchamannerduetoitslowshearforcetoensuretheintegrityofthestarchparticle,theyhavegoodwaterabsorptionperformanceafterheattreatment.Soitisnecessarytoexecuteelementratherthanthedistributionofthedispersedelementsofhybrid,thisisreferredtoinsection2.3inT.S.Emixturecanprovokeslottedscrewdesign,whenrotatingT.S.E.slottedscrewproductionbreakfastcereal,theflowoffoodparticlesbetweentheadjacentscrewaboltandforcedmixingandflow.3.2.1.ExperimentalExtruderisusingataperedrotaryextrudingmachinebytheCincinnatiMilacroncreate45type(CMA),breakfastcerealandtheidealheightofcoldpasteviscosity(CPV)manufacturedbycoarseflourasasubstitutefortraditionaldrum-dryproduct.Fig.7.Startandfinalresultofamultiplesteps.s.e.-developmentformeltingofsucroserglucosemixtures.MachineuseaverageL/D15eightholes,moldmaterialis4mmindiameter,onthewatercontentof25%feedcapacityis100kg/hofmaterialduringproductionweneedscrewvicespeedof80r/min.Grooveofscrewthreelengths(L1,L2,L3)inthepositionofthesecondparagraphstructureintothreescrews.ParagraphslengthL1(2x55mm),L2,L3(2x110mm),(2)x165mm.Productsampleandthedesignofthescrewisusedtodeterminetheviscosityoncoldpasteandhot.HighCPVcanprovidebetterbreakfastcerealsscoopcapacity,namelyhasgoodadhesiveness.Torepresentviscositydatausingtheso-calledtemperature-timedrivenbruntonviscometer,andblahunitofmeasurement.Thelimitingphenomenonduringmeltinginans.s.e.,istheexistenceofastationarylayerat2r3ofthescrewchannelheightrelatedtothescrewroot,wheresucrose.crystalsremainpresentwithoutadditionalmixing.Thisisapropertyofeachsinglescrewextruderprovidedwithanon-interruptedscrewchannel.Theheatpenetrationratefromthebarrelislow,duetothisphenomenon,whichmeansthatthetimeconsumingmeltingprocesscannotbeperformedintheavailableresidencetime.Theselectionofadistributivemixingelement,inthiscaseaso-calledpineapplehead,gavethesolution.Themixingfunctionoftheso-calledpineappleheadistodistributetheflowandtobringtheremainingsolidseedingcrystalstothehotboundarylayerattheinnersurfaceofthebarrel,wheretheywillmelt.3.2.2.ResultsanddiscussionFlowphenomenonBetweenkneadingpaddleandinversionelementhasanobviousdifferenceinmotion,inallinvestigationthesetpointofstagnationduetoreversecourseelementstobenoticed.Canclearlyseethetracerparticlesbeforefurtheraxialtransporttimeisonirregularmovement.Thisisconductedintheabsenceofkneadingpaddle,mixedinthesettingofstagnationpointthereisnotenough,forthefirstkneadingpaddlefloweffectwegiveadiagram(figure11)Inextrusion,mixingofsolidsandmeltshasalwaysbeenproblematic,leadingtodiversemodelsdescribingthemeltingprocess.Itisfoundthatforfoodsbasedoncereals,onlyafewarevalid,duetothesimultaneouspresenceofwaterandhighviscousnon-Newtonianmaterial.Mixingtrialsaresummarisedforsingleandtwinscrewextruders,withparticulatesolidsofdifferentparticlesizeslike,maizegrits,wheatflour,sucrosecrystalsandglucosesyrup.Specialmixing-headsforsinglescrewextruderslike,pineapple-heads,andslottedflightsectionsforcounter-rotatingtwinscrewextrudersareinvestigated.Theeffectsofscrewgeometryonmixinghasbeenmeasuredusingco-rotatingtwinscrewextrudermodularelementslike:singleleadelements,mixingpaddlesandreversedpitchelementsinatranslucentmodelextruderbymeansofastudyofflowphenomenaandresidencetimedistributionRTDmeasurements.Mixingeffectsarereportedandtheirinfluencesonviscousdissipation,residencetime,curvespreadandstagnancyareexplained.1999ElsevierScienceS.A.Allrightsreserved.Whenfoodparticlesduringtheirlifetimeinanextruderaresubjectedtoaxialmixing,thiscanbeseenandmeasuredbyachangingRTD.Extremesinthiscaseareplugflow,whereallparticleshavethesameresidencetime,orawideRTDwhichiscausedbyaxialmixing.Someparticleswillstayintheextrudercookerforaprocesstimeshorterthantheaverage,whilstotherswilldwellformuchlongerthantheaveragewhendifferentflowsystemsarecompiledseeFig.2.Fig.3showsthetheoreticalRTDforamaterialwithacoefficientns1inthepower-lawequationforthesheardependencyoftheviscosityinans.s.e.ThisfigurealsoshowstheRTDdata,measuredwhenprocessingcorngritsinaBattenfelds.s.e.attwomoisturey1.contentsvs0.142,0.20kgkgandscrewrevolu-wy1wxtionsrangingfromNs1.33,1.66,2.0revs22.TheRTDdataarerepresentedasancumulativeexitageorF-function,whichshowsthefractionFoftheinflow,wxwhichhaslefttheextruderaftertseconds3,4,16.TheE-function,thederivativeoftheF-function,showstheso-calledexitagedistributionoffoodparticles,fedintotheextruderataninfinitesmalltimeandisrelatedtotheF-functionwith:tFtsEtdt1H0Theaverageresidencetimetofthefoodmaterialinthecookingextruderiscalculatedwith:tstEtdt.2HWhentheF-functioninFig.3isobserved,itfollo