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TEAMEXPERIMENT1:FERROFLUID
JeremyTylerParsons
UniversityofColorado:MCEN5151-FlowVisualization11/3/2016
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IntroductionTheimageshownwascreatedforMCEN5151-FlowVisualizationfortheTeamIassignment.Theintentoftheassignmentwastoplanandconductanexperimentthatdemonstratesafluidphenomenonofinteresttotheteamandimagetheresults.Forthisexperiment,ourteamchosetoinvestigatetheintriguingphysicsofferrofluidandtheeffectsofintroducingmultiple,magneticfields.Thefollowingreportwilldetailtheexperimentalsetupandphotographictechniquesusedtocapturetheferrofluidimageshown,aswellasthefluidmechanicsdrivingthedynamicsoftheferrofluidillustratedintheimage.
FluidPhysicsFerrofluidwasoriginallydiscoveredbyNASAinthe1960’s,whenscientistswereinvestigatingpotentialmethodsofcontrollingfluidsinspace(1).Thebenefitsoftheuniquephysicalpropertiesofferrofluidswereimmediatelyobvious,astheflowcouldbedirectlyinfluencedwiththepresenceofamagneticfield. Ferrofluidisaveryuniquefluid,asitisactuallyastablecolloidaldispersionofnano-scaleferromagneticparticlesinacarrierliquid(2).Inthecaseoftheferrofluidweutilized,thecarrierliquidwasasimplemineraloilandtheparticlesweremostlikeaferritesuchasmagnetite,about10nmindiameter.Whenexposedtoamagneticfield,theparticlesreacttotheresultingmagneticforcesandthecarrierfluidactsasaproxytovisualizethedirectionandamplitudeofthemagneticfieldstheferrofluidisexposedto.Theshapeisduetoaneffectcallednormalfieldinstability(3).Thenormalfieldinstabilityresultswhenthenano-scaleparticlesintheferrofluidareinthemostfavorableenergystate.ThisisformulatedviaMaxwell’sequations,wherethedivergenceoftheBfieldiszeroandthecurlofHiszero.Thepresenceofamagneticfieldleadstoinducesapressuredifferentialattheinterfacebetweentheinternalofthefluidandthesurface.Thisdifferentialinpressurecausestheferrofluidtoelongateinthedirectionofthemagneticfieldthatisbeingapplied.Thepeak-to-peakspacingisproportionaltotheTaylorWavelengthforhydrodynamicinstabilities,whiletheamplitudeofeachspikeisafunctionoftheintensityofthemagneticfieldapplied.
Figure1:Maxwell’sEquationsofElectromagnetism(4)
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ExperimentalSetupTheimagewascreatedbyexposingtheferrofluidtotwoseparatemagneticfields,onesteadyandonedynamic.Todothiswecreatedanexperimentalsetuptomanipulatetheferrofluidusingstacksofneodymiummagnetsindifferentlocationstocreatethedynamicresponseoftheferrofluidtoeachmagneticfield.Awordofcaution:ferrofluidisnontoxicbutisextremelypronetostainingandcanpermanentlystainaboutanysurfaceitcomesincontactwith.Itisimportanttowearoldclothing,coveranysurfacesthatmaybestainedbytheferrofluidandconsidertheeffectsofeachstepintheexperimentontheferrofluidpriortoexecutingthem.Inordertominimizethisrisk,wecoveredthetablewewereshootingonwithplasticandsurroundedtheapparatuswithasheetoffoamtocontainanyaccidentalsplashdroplets.Itisalsoveryimportanttoavoidanydirectcontactbetweentheferrofluidandamagnet.Sincetheferromagneticparticlessuspendedinthecarrierfluidaresosmalltheywillbecomepermanentlyattachedthemagnet.Thusanymagnetsintroducedhadaboundaryinbetweenthem.Inourcaseweusedsheetsofacrylictoisolatethemagnetsfromtheferrofluidwhileintroducingeachmagneticfield.Theferrofluidwasplacedinasmallcontainerandthesheetsofacrylicwerethenplacedaboveandbelowthecontainer.Thefirststackofmagnetswasplacedagainsttheloweracrylicsheet,directlybeneaththesubjecttocreateasteadymagneticfieldfirst.Oncetheferrofluidhadformedasteady-statepatternonthesubject,thesecondstackofmagnetswasintroducedonagainsttheupper,acrylicsheet.Initially,thesecondmagneticfieldaddedwasaddedbyhanditwasverydifficulttocontrol.Thesubtledifferencesindistancehadadramaticimpactonthedynamicresponseoftheferrofluid.The“leap”fromthesubjecttotheupperacrylicsheetwastoofasttoimageproperly.Thusweintroducedtwoblocksofsoftfoamtocontroltheinitialheightoftheuppermagnetsandpressurecouldbeslowlyappliedtobringthemagnetsclosertotheferrofluid.Thisallowedforamuchmorecontrolledresponsethatcouldbemoreeasilydocumentedandofferedmuchmoreresolvedimages.Tocreateadiverserangeofresponsesfromthefluid,webroughtavarietyofironandsteelobjectsandintroducedthemintothefluidprogressivelythroughouttheexperiment.Eachobjectcreatedadifferentresponseinthesteady-stateanddynamicvisualsoftheferrofluid.Forreferencetheexperimentalsetupisshownbelow.
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PhotographicTechniqueTheimagewasshotonOctober14th,2016inadesignstudioinFlemingbuildingattheUniversityofColorado,usingaCanonRebelXTIdigitalDSLRcamera.Thefollowingequipmentandparameterswereusedtocapturetheimage:
• Lens:18-55mmMacroscopicLens• ShutterSpeed:1/60Second• ExposureSettings:ISO200,F/5.6• ImageResolution:Original-3888 × 2592pixels,Edited-1475 × 1536pixels• Editing:PhotoshopCS6wasutilizedforpostprocessingtheimage
Ashutterspeedof1/60swasutilizedtocapturetheferrofluiddynamicsasitleaptfromonemagneticfieldtothenext,asshownintheimage.OriginallyIleanedtowardafastershutterspeedsincethefluidwasmovingratherquicklyacrosstheframe.However,intheprocessofexperimentingwithbalancingapertureandshutterspeed,thisimagecamestoodoutamongtherestduringimport.Thefieldofviewintheoriginalimageisaboutsixinchesacrossintotalwhilethebottom“crown”oftheferrofluidisabout2incheswide.
Figure2:ExperimentalSetup
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PhotoshopCS6wasusedtopostprocesstheoriginalimageandfocustheviewer’sattentiontowardthefluidbeingvisualized.Theresolutionoftheinitialimagewas3888 × 2592pixelsandwascroppeddownto1475 × 1536pixelstoremoveanydistractingelementsfromthephotoandfocusonthephysicsoftheferrofluidbeingillustrated.Thebackgroundwasremovedtodrawisolatetheflowinquestionandthevibrancywasadjusteddownjustslightlytoreducesomeoftheintensityoftheglareoffoftheferrofluidspikes.Theoriginalandpost-processedimagesareshownbelow.OriginalImage EditedImage
CommentaryIhavealwaysfoundferrofluidtobeveryfascinatingandtheaestheticvisualscreatedbyitsuniquephysicalpropertiesmadetheexperimentveryenjoyabletoconduct.TheteamandIconcurthatwewouldalterthesetupifweweretoconductthisexperimentagain.ByincorporatingamorecontrolledbackgroundtheimagewouldhavetakenlesspostprocessingtoillustratetheflowclearlyandIthinkthiswouldhavelenttoincreasingtheoverallimagequality.Besidesthat,Istillenjoythisvisualoftheferrofluidinthefinalimage.Ithasaninteresting,almostalien,characterwhenexposedtothemagneticfieldsthatseemstojumpoffthepagetowardtheviewer.
AcknowledgementsIwishtoacknowledgeJosephStraccia,MaxScrimgeourandPeterBrunsgaardfortheircollaborationonthisteamassignment.Theywereinstrumentalinconductingtheexperimentandcreatingtheimagesillustratingthephysicsoftheferrofluid.Pleaserefertotheirworkformoreimageryandinformationregardingthisexperiment.
Figure4:OriginalImage,Unedited Figure3:FinalImage,AfterPostProcessing
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Citations1. "FerrofluidResources."ExploringtheNanoWorld.2008.AccessedNovember3,2016.
http://education.mrsec.wisc.edu/background/ferrofluid/.2. Odenbach,Stefan.Ferrofluids:MagneticallyControllableFluidsandTheirApplications.
Berlin:Springer,2002.3. Lin,Joshua."SpikesonFerrofluid?"PhysicsStackExchange.November29,2014.
AccessedNovember04,2016.http://physics.stackexchange.com/questions/149414/spikes-on-ferrofluid.
4. Watson,George."Maxwell'sEquations."December11,1997.AccessedNovember04,2016.http://www.physics.udel.edu/~watson/phys208/maxwell-review.html.