Download pdf - TEAM EXPERIMENT 1: FERROFLUID · experimenting with balancing aperture and shutter speed, this image came stood out among the rest during import. The field of view in the original

TEAMEXPERIMENT1:FERROFLUID

JeremyTylerParsons

UniversityofColorado:MCEN5151-FlowVisualization11/3/2016

MCEN5151 FlowVisualization 11/3/2016

2

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)


3

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.


4

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


5

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


6

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.