文献翻译-碳酸钙在AISI316管内污垢热阻模型的预测

英语翻译FoulingresistancemodelforpredictionofCaCO3scalinginAISI316tubesM.SultanKhan,S.M.Zubair,M.O.Budair,A.K.Sheikh,A.QuddusAbstract：Thetermfoulingisgenerallyusedtodescribethedepositionofunwanted(initiallyfluid)particles,whichincreasesbothresistancetoheattransferandpressuredropthroughtheheatexchanger.CaCO3whichispredominantlypresentinthecoolingwater,hasinversesolubilitycharacteristicsi.e.,itislesssolubleinwarmwater,resultingindepositionofscalesinheattransferequipment.Anexperimentalprogramisdescribedinthispapertostudythegrowthoffoulingasafunctionoftubesurfacetemperature,Reynoldsnumber,tubediameterandthetimeforwhichthetubehasbeensubjectedtothescaleformingsolution.Thedatacollectedfromtheexperimentsareusedtodevelopafoulingresistancemodel.Inaddition,theresultsobtainedfromthepresentstudyarealsocomparedwiththosediscussedearlierbyseveralinvestigatorswithregardtoCaCO3fouling.Keywords：scaling，theheatexchanger，CaCO31.IntroductionThedepositionofunwantedparticlesonthesurfacesofheatexchangersisdefinedasfouling.Thepresenceofthesedepositsrepresentsanadditionalthermalresistancetoheattransferwhichreducesthethermal-hydraulicperformanceoftheheattransferequipment.Thedepositionmaybecrystalline,biologicalmaterial,theproductsofchemicalreactionsincludingcorrosion,orparticulatematter1.Thegrowthofdepositsdependsuponanumberofparameterssuchasfluidcomposition(pHvalue,concentration,etc.),temperature,geometricdimensions,andReynoldsnumber(Re)oftheflowingfluid.DifferentaspectsofthedepositionprocessanditscharacterizationarediscussedinthepioneeringpaperofTaboreketal.2.Itshouldbenotedthatanunderstandingoftheeconomicpenaltiesassociatedwithfoulingisoneoftheprimaryreasonsforgreaterinterestinthefouling-relatedresearch.Pritchard3presentedcostestimatesassociatedwithfoulinginBritain.Thackery4estimatedtheoverallannualcostoffoulinginU.K.toabout0.3ofGNPfortheyear1978(approximately$1billion).TheorderofmagnitudesoftheseestimatesisconfirmedbyVanNostrandetal.5whileinvestigatingthefoulingrelatedcostsfortheU.S.specificrefineryunits.Steinhagenetal.6estimatedthefoulingrelatedcostsforNewZealandatabout$30to$46millionwhichisabout0.1-0.17%oftheannualGNPfortheyear1988.AprojecthasbeeninitiatedattheKingFahdUniversityofPetroleumandMinerals,Dhahrantostudytheimpactoffoulinginheatexchangers.Theobjectiveofthispaper,whichispartiallybasedontheabovementionedproject,istopresentafoulingresistancemodelofCaCO3scalinginAISI316stainlesssteeltubes.Inthisregard,aliteraturesurveyonprecipitationfoulingwithemphasisonCaCO3foulingisdiscussedinthenextsectionwhichisfollowedbydetailsoftestequipmentdesignandproceduretoobtainparametricexperimentalfoulingdata.Thedatathusobtainedfromthetestequipmentispresentedintheformofadimensionlessregressionmodel.2BackgroundofCaCO3foulingTheproblemoffoulingisencounteredinindustrialoperationsandprocesseswithnaturalwateroraqueoussolutionscontainingdissolvedinorganicsalts.Someofthesesaltsortheircombinationshaveinversesolubilitycharacteristics,sothattheyarelesssolubleinthehotfluidadjacenttotheheattransfersurface.ExamplesofsuchsaltsareCaCO3andCaSO4.Figure1showsthebehaviorofnormalandinversesolubilitysaltsolutions1.Fornormalsolubilitysaltsolution,atpointA,solutionisundersaturatedbutoncoolingtopointBitisjustsaturated.Onfurthercooling,thesolutionbecomessupersaturatedandcrystalnucleationoccursatpointC.AscrystallizationandcoolingproceedssolutionconcentrationfallsandmovesinthedirectionofD.NowforaninversesolubilitysaltsolutionitisundersaturatedatpointA,asitisheateditreachesthesolubilitylimitatpointBattemperature1andthenundercontinuedheatingthesolutionbecomessupersaturatedreachingpointCattemperature2whereprecipitationstarts.Theformationofscaleonheattransfersurfacesisacommonphenomenonwhereaqueoussolutionsareinvolved,e.g.theuseofnaturalwatersforcoolingpurposesorevaporativedesalination.Unlesssuitablemeasuresaretaken,theproblemofscaleformationcangiverisetoseriousconsequences.Insteamboilers,forinstance,thepresenceofscaleonwatersidecangiverisetohighmetaltemperaturesthatmayresultinmechanicalfailureofheat-transferequipment.Hanlon,asmentionedinreference1,commentedonthepotentialofscaleformationinindustrialequipmentisveryhigh.Asanexample,heobservedthatfora1milliongallon/daydesalinationplantundernormalconcentrationconditions,amaximumofabout1400kgofCaCO3couldbeprecipitatedeachday.Intermsofscalethickness,itwouldrepresentabuildupof0.1mmperdayonthetotalheatexchangersurfaceswithinatypicalplant.Althoughthismayberegardedasanextremeexampleitdoesillustratethemagnitudeofscalingorcrystallizationfoulingproblemsinindustrialplants.AsystematicstudyofscalingcharacteristicsofcoolingtowerwasconductedbyMorseandKnudsen7.EffectofsurfacetemperatureonthescalingbehaviorwasdiscussedbyStoryandKnudsen8.LeeandKnudsen9designedanexperimentalapparatustosimulatetheoperatingconditionsofacoolingtower.Thisisasomewhatextensiveinvestigationtodeterminetheeffectofflowvelocity,surfacetemperatureandwaterqualityonscalingofexchangertubes.CoatesandKnudsen10havediscussedresultsoftheirexperimentsconductedforobtainingdataregardingCaCO3scaling.WatkinsonandMartinez11studiedscalingduetoCaCO3incoppertubesunderconditionsthatpromoterapidandseverescaling.Inthisregard,artificiallyhardenedwaterofhighdissolvedandsuspendedsolidswascirculatedthroughaheatedtestsection.Effectsofflowvelocity,tubediameterandbulktemperatureonasymptoticfoulingresistancehavebeendetermined.Manzoor12conductedfoulingrelatedexperimentsandstatisticallyanalysedCaCO3foulingdata.TheobjectiveofManzoorsstudywastodemonstratethatfoulingresistancevariesfrompointtopointalongahorizontaltubeandalsoforthesamepointitvariesfromreplicatetoreplicate.Theoperatingparametersweretemperature,pressure,solutionconcentrationandvelocitywhichwerekeptconstantduringtheexperiments.Konings13onthebasisofexperimentalworkwithcoolingwater,treatedbydifferentmethodstoeliminatescaling,presentedatableofguidevaluesforthefoulingresistance.Anexperimentalstudyoftube-sidefoulingresistanceinwaterchilledevaporatorwascarriedoutbyHaideretal.14inwhich12.6ftlongevaporatortubeswereusedandfoulingdataweretakenforfourtubegeometries.Nodataweretakenatdifferentsectionsofthetube.ThefoulingcharacteristicsofcoolingwaterforprecipitationandparticulatefoulingarealsodiscussedbyKnudsen15whereheemphasizedseriousproblemswhenheatexchangersareoverdesignedduetotheuseofincorrectdesignfoulingallowance.Practicalandfundamentalaspectsofprecipitationfouling(CaCO3scaling)werereviewedbyHasson16.Heconsideredtheproblemofdefiningprecipitationfoulingtendencybyreviewingprinciplesofsolutionequilibriaandprecipitationkineticsforsaltsystemsfrequentlyencounteredinheatexchangerapplications.BranchandMuller-Steinhagen17developedamodelforfoulinginshellandtubeheatexchangersbyconsideringHassonsionicdiffusionmodelforCaCO3scaling.Hesselgreaves18discussedtheeffectofsystemparametersonthefoulingperformanceofheatexchangers.AmodelforCaCO3scaleformation,whichgivesreliablepredictionofthefoulingratewithalterationoffeedwaterchemistry,wasdevelopedbyTretyakovetal.19.Itshouldbenotedfromtheabovestudiesthatsofarnofoulingresistance(f)modelhasbeendevelopedthatmaypredictfasafunctionof,tubesurfacetemperatureandtubediameter.3TestequipmentdesignThetestapparatuswasadouble-pipecounter-flowheatexchangerasshowninFig.2.Theworkingfluidwaspassedthroughtheinnertubecomprisedofsixtestsections,each0.1524mlong.Toheatupthesurfaceoftheinnertube,hotwaterwascirculatedintheoutertubeusingaConstant-TemperatureWater-CircultorBath(CTWCB),whichhadaprovisionofvariabletemperaturesettings.Threeheatexchangerswerefabricatedwithinnertubesizesof1/4in(0.00635m),3/8in(0.00952m)and1/2in(0.0127m).Theoutertoinnerradiiratiooftubeswassetatfourforallthreeheatexchangers.AllfittingsweremadeofAISI316.Tosimulatetheconditionsencounteredincoolingwatersystems,Na2CO3andCaCl2solutions,preparedinde-mineralized(distilled)waterwereusedtoproduceCaCO3asaproductofchemicalreaction.Theproductsolution,whenpassedthroughtheinnertuberesultedinthedepositionofCaCO3scaleontheinnersideofthetube.ThechemicalreactiontoproduceCaCO3scaleisgivenby20OxHNaClCONaxHCal23322Thechemicalsolutionswerepre-heated,separately,usingpre-heatersandheatingtapestoachieveatemperatureof50Cbeforethesolutionenteredtheheatexchanger.ThesystemisaoncethroughtypeandaBackPressureRegulator(BPR)wasusedtomaintainapressureof689kPaattheendoftheheatexchanger.Figure3showsthescalingapparatuswhichconsistsoftwohighpressurevariablestrokepumps,storagetanksforthechemicalsolutions,pre-heaters,heatingtapes,CTWCB,thermocouples,temperaturecontrollersandaBPR.Additionaldetailsanddescriptionofthetestapparatusarepresentedinreference21.4ExperimentalprocedureTheconcentrationoftheproductsolutionwaskeptconstantat0.0006mol/l.Thisrequired2.543and3.528gofNa2CO3andCaCl2,respectively,tobemixedin40lofdistilledwater.TheparametersthatwerevariedduringtheexperimentsareReynoldsnumber,surfacetemperatureanddiameteroftheinnertube.ItshouldbenotedthatexperimentswereconductedforallpossiblecombinationsoftheparametervaluesasshowninTable1,inwhichReynoldsnumberisbasedontheinnerdiameterofthetestsections.Asalreadymentionedthreeheatexchangersweredesignedandfabricatedforthethreetubesizes.Foraparticularsize,ReynoldsnumberwasfixedandvariousexperimentswereconductedbyvaryingthesurfacetemperaturesoftheinnertubebythehelpoftheCTWCB.Twohourscontinuousoperationofthetestisreferredtoasatestrun.Oneexperimentconsistedoffive2hrunsforaparticularsetofparameters.Attheendofeachrun,theheatexchangerwasdismantledandthetestsectionsweredriedintheoven.Massgainofthetestpiecesduetoscalingwasthenmeasuredusingananalyticalweighingscalewhichhadanaccuracyof1mg.Theheatexchangerwasthenre-assembledforthenextexperimentalrun.Itwasobservedthat0.25in(0.0127m)tubeblockedduetoscalingafter10hofoperationthusrestrictingthedurationoftheexperimentstoamaximumof10hours.PeriodicmeasurementsoftheflowrateswerecarriedouttomaintainaconstantReynoldsnumberduringtheentireexperiments.Forthenextsetofexperiment,newsetoftubeswereused.Usingthemassgainmethod,foulingresistance(f)wasdeterminedasfollows:where2istheinsideradiusofthetube,1istheaveragevalueofradiuskrRf12duetothedepositforaparticulartestsectionwhichcanbecalculatedbyusingtherelationlmasginr215ConcludingremarksThefoulingresistancedataofCaCO3scalingwerepresentedtostudytheinfluenceoftubesurfacetemperature,Reynoldsnumberandtubediameter.ItwasobservedthattheinfluenceofReynoldsnumberintherangeinvestigated(9001700)wasalmostnegligible,whichwasalsonoticedbyLeeandKnudsen9whohavepresentedthesameconclusionfortheirexperimentaldataonasymptoticfoulingresistance.Theyhadobservedthatbyvaryingthefluidvelocitiesfrom3to10ft/s(0.91to3.05m/s)therewasnoprofoundeffectontheamountofCaCO3foulingresistance.However,theinfluenceoftubesurfacetemperatureandtubediameteronthefoulinggrowthwasfoundtobeappreciablefortherangeinvestigated.ThereasonsfortheincreasedfoulingresistanceasafunctionofsurfacetemperatureanddiameterwereexplainedbyconsideringtheinversesolubilitycharacteristicsofCaCO3andtubesurfaceeffects.Thedataobtainedfromexperimentsarepresentedintheformofadimensionlessfoulingresistancemodelforestimationandpredictionpurpose.Inthisregard,allthevariablesinthemodelarenon-dimensionalizedwithrespecttotherespectivemaximumvaluesconsideredinthisstudy.Themodelthusdevelopedhasbeeninvestigatedinsomewhatmoredetailbyobservingthenormalprobabilityplotofresiduals.Inaddition,severalotherstatisticalchecksarealsomadetoassessthesuitabilityofthemodel.Noapparentmodeldefectsarenoticed.Itisthusconcludedthatthefoulingresistancemodelmaybeconsideredasareliablemodelwithintherangeofexperimentalparametersinvestigatedinthepresentstudy.References1.Bott,T.R.:FoulingofHeatExchangers.Elsevier,Netherlands(1995)2.Taborek,J.;Aoki,T.;Knudsen,J.G.:Fouling,themajorunresolvedprobleminheattransfer.Chem.Eng.Progress68-2(1972)59673.Pritchard,A.M.:Fouling-Scienceorart.In:E.F.C.SomerscalesandJ.G.Knudsen(Eds.).HeatTransferEquipment.Hemisphere,Washington,D.C.(1981)4.Thackery,P.A.:Thecostoffoulinginheatexchangerplant.In:A.M.Pritcard(Ed.),Fouling-ScienceorArt.Guildford,UnitedKingdom(1979)5.VanNostrand,W.L.;Leach,S.H.;Haluska,J.L.:Economicpenaltiesassociatedwiththefoulingofrefineryheattransferequipment.In:E.F.C.SomerscalesandJ.G.Knudsen,(Eds.),FoulingofHeatTransferEquipment,Hemisphere,Washington,DC(1981)6.Steinhagen,R.;Steinhagen,H.M.;Maagni,K.:ProblemsandcostsduetoheatexchangerfoulinginNewZealandIndustries.HeatTransferEng.11-7(1993)19307.Morse,R.W.;Knudsen,J.G.:Effectofalkalanityonthescalingofsimulatedcoolingtowerwater.CanadJ.Chem.Eng.55(1977)2722788.Story,M.;Knudsen,J.G.:Theeffectofheattransfersurfacetemperatureonthescalingbehaviourofsimulatedcoolingtowerwater.AIChESymp.Ser.74-1124(1978)25309.Lee,S.H.;Knudsen,J.G.:Scalingcharacteristicsofcoolingtowerwater.ASHRAETrans.85-1(1979)28130210.Coates,K.E.;Knudsen,J.G.:Calciumcarbonatescalingcharacteristicsofcoolingtowerwater.ASHRAETrans.86-2(1980)689111.Watkinson,A.P.;Martinez,O.:Scalingofheatexchangertubesbycalciumcarbonate.JHeatTransfer97(1975)50450812.Haq,M.U.:Reliability-basedmaintenancestratigiesforheatexchangerssubjecttofouling.MastersThesis,KingFahdUniversityofPetroleumandMinerals,SaudiArabia(1995)13.Konings,A.M.:GuideValuesforthefoulingresistancesofcoolingwaterwithdifferenttypesoftreatmentfordesignofshell-andtubeheatexchangers.HeatTransferEng.10-4(1989)546114.Haider,S.I.;Meitz,A.K.;Webb,R.L.:Anexperimentalstudyoftube-sidefoulingresistanceinwater-chiller-floodedevaporators.ASHRAETrans.98-2(1992)86103.15.Knudsen,J.G.:Copingwithcoolingwaterfoulingintubularheatexchangers.AIChESymp.Ser.85-267(1989)11216.Hasson,D.:Precipitationfouling.In:E.F.C.SomerscalesadJ.G.Knudsen,(Eds),FoulingofHeatTransferEquipment.Hemisphere,Washington,DC(1981)17.Branch,C.A.;Steinhagen,H.M.M.:Influenceofscalingontheperformanceofshell-and-tubeheatexchangers.HeatTransferEng.12-2(1991)378518.Hesselgreaves,J.E.:Theeffectofsystemparametersonthefoulingperformanceofheatexchangers.ICHEMESymp.Ser.129(1992)995100619.Tretyakov,O.V.;Kristskiy,V.G.;Styazhkin,P.S.:Improvedpredictionoftheformationofcalciumcarbonatescaleinheatexchangersofsecondaryloopsofconventionalthermalandnuclearpowerplants.HeatTransfer-Sov.Res.23(1991)53253820.Masterten,W.L.;Hurley,C.N.:Chemistry,PrinciplesandReactions.Saunders,Philadelphia(1989)21.Khan,M.S.:Effectofthermal-hydraulicparametersonCaCOscalinginheatexchangers.MastersThesis,KingFahdUniver3sityofPetroleumandMinerals,SaudiArabia(1996)22.Parry,D.J.;Hawthorn,D.;Rantell,A.:FoulingofPowerStationCondenserswithintheMidlandsRegionoftheC.E.G.B.,In:Somerscales,E.F.C.andKnudsen,J.G.(Eds.)FoulingofHeat.TransferEquipment.Hemisphere,Washington,DC(1979)23.Montgomery,D.C.;Peck,E.A.:IntroductiontoLinearRegressionAnalysis.Wiley,NewYork(1985).碳酸钙在AISI316管内污垢热阻模型的预测摘要：结垢此术语常常用来描述不期望的会加大热交换器的压力降和热阻的颗粒(最早在液体中)的沉降。可知，碳酸钙主要存于冷却水当中，有难溶的特点，因为其难溶于热水，导致它在热交换设备中的结垢沉降。此篇论文目的在于研究有关管子表面的溶液，雷诺数，温度和在管子中结垢时间和污垢增长关系，将描述一个的实验项目。从当今研究中得到的结果也被用来与早些时候部分调研人员关于碳酸钙结垢的讨论进行比较。另外，来自实验中的数据被用来建立一个污垢热阻模型关键词：结垢，热交换设备，碳酸钙1.绪论这些沉积的存在会表现出附加的热阻，将会降低热交换设备的水传热性能。沉积的增加取决与包括液体成分（pH值，浓度等），温度，几何尺寸和流体雷诺数在内的一系列参数。结垢是指非期望颗粒在热交换器表面的沉积这些沉降物可能是包括腐蚀、颗粒物质在内的化学反应产物或者结晶生物物质。在Taborek等人早期的论文中对沉积过程的不同方面及其特性进行了讨论。应该注意到结垢所造成的经济损失是结垢相关研究的一个主要原因。Pritchard提出了英国在结垢方面的大概成本。VanNostrand等人在调查了美国精炼厂之后确认了这些估计。Steinhagen在1985年在新西兰，污垢造成的损失约占当年国民生产总值的0.1-0.17%，约为3000-4600万美元。Thackery在1973年英国污垢所造成的全部损失大约是当年国民生产总值的0.3（大约为10亿美元）。在这方面，一篇有关碳酸钙结垢的调查将在下一个有相关实验设计细节和获得实验性的结垢数据的程序的部分被讨论。本篇论文部分是根据此项目，其目的是提出碳酸钙在AISI316不锈钢管子内沉积的污垢热阻模型。因此，这些数据将以一个无量纲衰退模型的形式来提出。为了研究结垢对热交换器的影响，Dhahran的KingFahdUniversityofPetroleumandMinerals发起了一个项目。温度温度2.碳酸钙结垢的背景在有无机盐水溶液或天然水的工业过程和操作中，常常会遇到结垢的问题。一些盐或它们的组成具有溶解度低的特点，所以较难溶解在与热交换器表面相邻的热流体内，例如硫酸钙和碳酸钙。图1表示不溶性盐和普通的盐的表现。对于一般的可溶性盐的解决方法：观点一，在较进一步的冷却上，解决变成使过度饱和而且水晶成核。观点三，集中解决结晶和冷却的问题。观点二，解决不溶解但是在冷却上指出它是饱和的。观点四，现在对于相反的方向移动的可溶性盐解决，如同它是一样加热温度到点B到达可溶性界限，随后在继续的加热解决之下变成过度饱和，到达温度点C，开始坠落。换热器表面水垢的形成是十分常见的现象（包括水溶液），例如，使用天然水来冷却或者蒸发脱盐。除非采用适当的措施，不然水垢将会引起严重的后果。例如，蒸发器里水垢引起的高金属温度可能导致换热设备机械失灵。上文提到的Hanlon认为工业设备中水垢的位势事非常高的。转化成水垢厚度相当于换热器表面全面积的0.1毫米。虽然这可能事一个极端的例子，但是它确实说明了工业设备水垢的大小或者析晶结垢的问题。Story和Knudsen讨论了水垢表面温度的影响。Lee和Knudsen设计了一个冷却塔试验装置模拟操作情况。这项调查略带广泛性，目的是研究热交换器管道上流速，表面温度个水质对结垢的影响。Coates和Knudsen已经讨论他们为了获得与碳酸钙结垢有关的的数据而进行的的试验。Watkinson和Martinez研究了碳酸钙在铜管内快速又剧烈的结垢作用。在这方面，高度溶解的人工硬水和悬浮固体在一段热测试部分循环，然后测定出流速，管直径和温度对