化工专业英语电子教案.docx
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化工专业英语电子教案.docx
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化工专业英语电子教案
ChemicalEngineeringandEnvironmentalProtectionSubjectEnglish
1.ChemicalReactions
Concept:
Chemicalreactionisaprocessthatleadstotransformationofonesetofchemicalsubstancestoanother.Chemicalreactionscanbeeitherspontaneous,requiringnoinputofenergy,ornon-sponaneous,oftencomingaboutonlyaftertheinputofsometypeofenergy,heat,lightorelectricity.Classically,chemicalreactionsencompasschangesthatstrictlyinvolvethemotionofelectronsintheformingandbreakingofchemicalbonds,althoughthegeneralconceptofachemicalreaction,inparticularthenotionofachemicalequation,isapplicabletotransformationsofelementaryparticles,aswellasnuclearreactions.
Thesubstance/substancesinitiallyinvolvedinachemicalreactionarecalledreactants.Chemicalreactionsareusuallycharacterizedbyachemicalchange,andtheyyieldoneormoreproducts,whichusuallyhavepropertiesdifferentfromthereactants.
Differentchemicalreactionsareusedincombinationinchemicalsynthesisinordertogetadesiredproduct.Inbiochemistry,seriesofchemicalreactionscatalyzedbyenzymesformmetabolicpathways,bywhichsynthesesanddecompositionsordinarilyimpossibleinconditionswithinacellareperformed.
Chemicalreactionsinvolvetheruptureorrearrangementofthebondsholdingatomstogether,neveratomicnuclei.Thetotalmassandnumberofatomsofallreactantsequalsthoseofallproducts,andenergyisalmostalwaysconsumedorliberated.Understandingtheirmechanismsletschemistsalterreactionconditionstooptimizetherateortheamountofagivenproduct;thereversibilityofthereactionandthepresenceofcompetingreactionsandintermediateproductscomplicatethesestudies.Reactionscanbesyntheses,decompositions,orrearrangements,ortheycanbeadditions,elimination,orsubstitutions.Examplesincludeoxidation-reduction,polymerization,ionization,combustion(burning),hydrolysis,andacid-basereaction.
Chemicalchangerequiresachemicalreaction,aprocesswherebythechemicalpropertiesofasubstancearealteredbyarearrangementoftheatomsinthesubstance.Ofcoursewecannotseeatomswiththenakedeye,butfortunately,therearcanumberofcluesthattelluswhenachemicalreactionhasoccurred.Inmanychemicalreactions,forinstance,thesubstancemayexperienceachangeofstateorphase-asforinstancewhenliquidwaterturnsintogaseousoxygenandhydrogenasaresultofelectrolysis.
Essentially,achemicalreactionistheresultofcollisionsbetweenmolecules.Accordingtothiscollisionmodel,ifthecollisionisstrongenough,itcanbreakthechemicalbondsinthereactants,resultinginarearrangementoftheatomstoformproducts.Themorethemoleculescollide,thefasterthereaction.Increaseinthenumbersofcollisionscanbeproducedintwoways:
eithertheconcentrationsofthereactantsareincreased,orthetemperatureisincreased.Ineithercase,moremoleculesarecolliding.
Increasesofconcentrationandtemperaturecanbeappliedtogethertoproduceanevenfasterreaction,butratesofreactioncanalsobeincreasedbyuseofacatalyst,asubstancethatspeedsupthereactionwithoutparticipatinginiteitherasareactantorproduct.Catalystsarethusnotconsumedinthereaction.Oneveryimportantexampleofacatalystisanenzyme,whichspeedsupcomplexreactionsinthehumanbody.Atordinarybodytemperatures,thesereactionsaretooslow,buttheenzymehastensthemalong.Thushumanlifecanbesaidtodependonchemicalreactionsaidedbyawondrousformofcatalyst.
Reactiontypes:
Somecommonkindsofreactionsarelistedbelow.Notethatitisperfectlypossibleforasinglereactiontofallundermorethanonecategory:
Isomerisation,inwhichachemicalcompoundundergoesastructuralrearrangementwithoutanychangeinitsnetatomiccomposition;
Directcombinationorsynthesis,inwhich2ormorechemicalelementsorcompoundsunitetoformamorecomplexproduct:
N2+3H2→2NH3
Chemicaldecompositionoranalysis,inwhichacompoundisdecomposedintosmallercompoundsorelements:
2H2O→2H2+O2
Singledisplacementorsubstitution,characterizedbyanelementbeingdisplacedoutofacompoundbyamorereactiveelement:
2Na(s)+2HCl(aq)→2NaCl(aq)+H2(g)
Metathesisordoubledisplacementreaction,inwhichtwocompoundsexchangeionsorbondstoformdifferentcompounds:
NaCl(aq)+AgNO3(aq)→NaNO3(aq)+AgCl(s)
Acid-basereactions,broadlycharacterizedasreactionsbetweenanacidandabase,canhavedifferentdefinitionsdependingontheacid-baseconceptemployed.Someofthemostcommonare:
Arrheniusdefinition:
AcidsdissociateinwaterreleasingH3O+ions;basesdissociateinwaterreleasingOH-ions.
Bronsted-Lowrydefinition:
Acidsareproton(H+)donors;baseareprotonacceptors,includingtheArrheniusdefinition:
Acidsareelectron-pairacceptors;baseareelectro-pairdonors.
Redoxreactions,inwhichchangesinoxidationnumberofatomsininvolvedspeciesoccurred;thosereactionscanoftenbeinterpretedastransferencesbetweendifferentmolecularsitesorspecies.Anexampleofaredoxreactionis:
2S2O32-(aq)+I2(aq)→S4O62-(aq)+2I-(aq)
InwhichI2isreducedtoI-andS2O32(thiosulfateanion)isoxidizedtoS4O62-.
Combustion,akindofredoxreactioninwhichanycombustiblesubstancecombineswithanoxidizingelement,usuallyoxygen,togenerateheatandformoxidizedproducts.Thetermoxidationofasinglefunctionalgroupisnotcombustion.
C10H8+12O2→10CO2+4H2O
CH2S+6F2→2CF4+2HF+SF6
Disproportionationisaredoxreactioninwhichonereactantformingtwodistinctproductsvaryinginoxidationstate.
2Sn2+→Sn+Sn4+
Organicreactionsencompassawideassortmentofreactionsinvolvingcompoundswhichanorganiccompoundmaytakepartarelargelydefinedbyitsfunctionalgroups.
Exercise
1.PutthefollowingintoChinese
Exothermicreaction,chemicalreactionrate,sulfonationreaction,additionreaction,additionpolymerization,reversiblereaction
2.PutthefollowingintoEnglish
离子方程式,离子反应,裂解,取代反应,水解反应,反应,皂化反应,焰色反应,银镜反应,酯化反应,化学反应产物,合成反应
2.HeatExchanger
Aheatexchangerisadevicebuiltforefficientheattransferfromonemediumtoanother.Themediamaybeseparatedbyasolidwall,sothattheynevermix,ortheymaybeindirectcontact.Theyarewidelyusedinspaceheating,refrigeration,airconditioning,powerplants,chemicalplants,petrochemicalplants,petroleumrefineries,naturalgasprocessing,andsewagetreatment.Onecommonexampleofaheatexchangeristheradiatorinacar,inwhichtheheatsource,beingalotengine-coolingfluid,water,transfersheattoairflowingthroughtheradiator(i.e.theheattransfermedium).
Typesofheatexchangers
1.shellandtubeheatexchanger
shellandtubeheatexchangersconsistofaseriesoftubes(Figure1).Onesetofthesetubescontainsthefluidthatmustbeeitherheatedorcooled.Thesecondfluidrunsoverthattubesthatarebeingheatedorcooledsothatitcaneitherprovidetheheatorabsorbtheheatrequired.Asetoftubesiscalledhetubebundleandcanbemadeupofseveraltyplesoftubes:
plain,longitudinallyfinned,etc.Shellandtubeheatexchangersaretypicallyusedforhigh-pressureapplication(withpressuresgreaterthan30barandtemperaturesgreaterthan260oC).Thisisbecausetheshellandtubeheatexchangersarerobustduetotheirshape.
Theshellandtubeexchangercanbedividedintocarbonsteeltubeheatexchanger,stainlesssteeltubeheatexchangerandcarbon-steel-and-stainless-steeltubeheatexchangeraccordingtodifferentmaterials;theshellandtubeheatexchangercanbealsodividedintofixedtube-sheettypeheatexchanger,floatingendtypeheatexchanger,andU-typetubeheatexchangeraccordingtodifferenttubeforms;andaccordingtodifferentstructurestyles,theshellandtubeheatexchangercanbedividedintosingletubepass,doubletubepassandmultipletubepassheatexchanger,Theshellandtubeheatexchangerhasaheattransferareaof0.5~500m2,whichcanbecustomizedaccordingtotheusers’requirements(Table1).
Table1Shellandtubeheatexchangerspecifications
nominal
diameter
numberoftubepasses
numberoftube
HeatTransferAreanominalvalue/calculatingvalue
TubepassPassagesectionalareatubepassPassageFlowvelocity:
0.5m/secflowratem/hr
nominalpressure
tubelength/m
Ф25×2.5
1500
2000
3000
4000
6000
Ф25×2
600
1
269
60/62.7
85/83.88
125/126.13
0.0845/0.0932
152.10/167.76
2.Plateheatexchanger
Anothertypeofheatexchangeristheplateheatexchanger.Oneiscomposedofmultiple,thin,slightly-separatedplatesthathaveverylargesurfaceareasandfluidflowpassagesforheattransfer.Thisstacked-platearrangementcanbemoreeffective,inagivenspace,thantheshellandtubeheatexchanger.Advancesingasketandbrazingtechnologyhavemadetheplate-typeheatexchangerincreasinglypractical.InHVACapplications,largeheatexchangerofthistypearecalledplate-and-frame;whenusedinopenloops,theseheatexchangersarenormallyofthegaskettypetoallowperiodicdisassembly,cleaning,andinspection.Therearemanytypesofpermanently-bondedplateheatexchangers,suchasdip-brazedandvacuum-brazedplatevarieties,andtheyareoftenspecifiedforclosed-loopapplicationssuchasrefrigeration.Plateheatexchangersalsodifferinthetypesofplatesthatareused,andintheconfigurationsofthoseplates.Someplatesmaybestampedwith“chevron”orotherpatterns,whereothersmayhavemachinedfinsand/orgrooves.
Plateheatexchanger-heattransferplatesarecharacterizedbyoptimumembossingresultinginhighheattransfercoefficients(Tabl
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