Page 67 - konishipaper

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T. KONISHI and A. lTo
becausehighheatevaporationwasneededtocause suf ficientconvection.A Pyrexfueltrayof20mmwidthx 30mmdepthx120mmlengthwasused.Thesidesofthe.fueltraywere2mmthick.Chromel-Alumelthermo- coupJesof50-mmdiameterwereusedtomeasurethetemperatureofliquidfuelandatmosphere.Oneofthem wasinsertedintotheliquid1mmunderthesurfacewiththejunctionlocatedatthecen-terofthetray.Air temperaturewasmeasuredat10cmabovethefuelsurface.
A schematicdiagramofthemeasurementsystemsisshowninFig.2.Thelightsourceforaholographic i~terferometer isa5m WHe-Nelaser;thelaserbeamisdividedintotwobeamsbyapartialyr~flecting miror. Theobjectandreferencewavesinterferewitheachotherattheholographicplate~ A reaI-timeholographic interferometrywasused.1neachexperimen七theinterferogramforthereferenceconditionwasphotographed withal-sexposuretirne.ThehologramswererecordedonaAgfa-Gevaert10E75glasplate，and-developedfor 2minitesinRefinal.TheresultingfringeshiftcausedbyevaporationwererecordedbyaCCDcamerawithan exposuretimeof1/250sand'canbeacuratelyinterpretedbyimageprocesing.
Themeasurementsofthesurfacetemperaturewereaccomplishedbyusinganinfraredcamerahavinga spectralrangeof8.12μm，temperatureresolutionof0.1oCandtimeresolutionof30msec.Infraredelectromagnetic wavesemitedfromthefuelsurfacewerereflectedonagoldmirorandcanbetakenbyaninfraredcamera.An IRcamerawascalibratedbyaCopper-Constantanthermo-couplesof75mmdiameterplacedonthemethanol surface.Itwasfoundthattheemisivityofamethanolis0.96.
Toobservetheconvectivemotioninthesub-surfacelayer~ 10~20μm-diameter aluminumparticleswere sprinkled ontotheliquidsurface.Usingthe400mW Ar-ionlaserbeamandacylindricalensforaparticletrack velocimetry，a1mmthicklasershetwasestablishedwithanapproximately35degreeopeningangle.The trajectoriesoftheseparticleswererecordedbyeitherahomevideocameraorahighspeedcamera.
3.
Fig.l.Aschematicdiagramofhighsped shutersystem.
RESULTSANDDISCUSSION
Fig.2.Aschematicdiagramofexperimental aparatus.
χ:
Goldmiror
~
A seriesofpicturesthatdemonstratetheinfraredphotographsoftheliquidsurfacetemperatureatthe
0 liquidbulktempera旬 reTf=30oCinFig.3(a)，interferogramsinsidetheliquidphaseatTf=15CinFig.3(b)and
theinterferogramsofthegasphase atTf=30oC areshowninFig.3(c).Numbersindicatedintheleftsideofthe picturesarethetimee]apsedfromtheonsetofevaporation.
IntheinfraredphotographsshowninFig.3(a)，thetemperatureoftheliquidsurfaceisindicatedbythe densityofgrayscale，i.e.temperatureincreaseswithincreasedbrightnes.Itwasobservedthati1l-definedsmal scalecelsofwavelengthlmmformedafter0.2secondfromtheonsetofevaporationandthende:velopedinto polygonalcels.Thequasi-steadystateconditionwasreachedat2secondsfromtheonsetofevaporation.These celsareabout4mmwavelengthinsizeandmovebackandforthonthesurface.Thetemperatureatthecenterof thecel，whichisindicatedbybrightarea，is0.50 Chigherthanthatofnodalines.Asthesurfacetensionforce decreaseswithincreasingsurfacetemperature，theliquidsurfaceatthecenterofthecelispuledawaylateraly. Thismayleadtothecircularmotionwhichisupflowbeneaththecenterofthecelanddownflowbeneaththe nodaline.
AseriesofinterferogramsintheliquidphaseisshowninFig.3(b).Onefringeshiftcorespondstothe temperaturediferenceof0.080 Cformethanolwith20mmpathlength.Fortheinterferogramsobtainedearlyin theprbces，fringesareparaleltotheliquidsurface.Unfortunatelya-darklayercoversthefringesnearthesurface， whichisfromrefractionoflightduetomeniscusnearthePyrexwal，anddificulttoeliminateinthissystem.A