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muchastheIRtemperaturemeasur81nenttechnique wasfirstintroducedforuseinflamespreadmeasure- mentsin1993，ithasbecomeahandytolforthe measurementoftransient2-Dtemperatureprofiles insolidfuels.4，5 TheIRtechniqueprovedtobepar- ticularlyusefu1forthemeasurementoftheupward 丑amespreadwhereneitherthethermocoup1emea- surementnorvisua1observationfailstoobtainatem- pora12-Dprofi1eofthepyro1ysisfrontwherethe spreading宜amestabi1izes.
Thereareon1yafewexamples6oftheaplic'ationof theIRtechniquetomeasurethesurfacet81nperature of1iquidfuel，紅ldtherearenostudies，toourknow1- edge，thathaveadresedtheacuracy，measure- ment characteristics，and limitations of the IR technique. Wediscuswhatkindofmodifications wouldberequiredtoap1ytheIRtechniquetomea- suretransient2-Dprofi1esof1iquid-surfacetemper閏 atures.
WeprovideacomparisonbetweentheIRsolidand theIRliquidtemperaturemeasurements. (1)For liquid-fue1temperaturemeasurements，a surface- tension-driven丑owcou1dappearontheliquidsurface whenacertaintemperaturediferenceexistsonthe fue1surface. Whentheliquidstoragetanksystem undergoes a sudden change in pres sure，sloshing couldocur，whichwouldgeneratesurfacewaves. Forthesolidfue1，however，thereisneithersurface 丑ownorsurfacewave. (2)Thetemperatureofthe 1iquidsurfaceofourinterestisinthe0-50oCrange， whereas the typica1 temperature of pyr10rizing a solid-fuelsurfaceisaproximately350oC. Point(1) requirestheIRliquidmeasurementtechnique，as hasbeendemonstratedbyItoetal.，7tohaveafaster response time and beter temperature resolution thanwiththeIRsolidtemperaturemeasurement. Point(2)requirestheIR1iquidtemperaturemea- surementtobemoresensitiveatthe10wertempera- ture range than with the IR solid temperature measurement.
IRcamera
2. E){perimentalMethod
A. MeasurementoftheEmisivityofLiquid
br叫 ionmethod.
B. MeasurementofInfraredAbsorptionwithPropanol
Vapor
Figure1showsthePyrexexperimenta1aparatus (15-cmdiameterby2-cmheight)thatwasusedto measuretheemisivityof1iquidpropanoL AnIR camerawasp1acedovertheliquidsurface，alowing directobservationofthefue1surface. TheIRcam- erahasan8-12-μmspectralrange，atemperature resolutionof0.1oC，andaresponsetimeof30ms.
OurIR)camerarequiresemisivityofthemeasur- 泊gtargetmaterialtobeknown. Liquidpropano1 waspouredintothePyrexcontainerthatwasposi- tionedonanelectricheate士p1atethroughasilicon rubermat. The1iquidpropanolwasheatedgrad- ual ly 企 o m room temperature (20 0 C) to ap proxi- mately80oC. Thentheheaterwasturnedofand the propano1 was co o1ed to room temperature by forcedconvection. Duringthisproces，theIRcam- era(withanemisivityof1)anda五nethermocouple measuredthesameliquidspottemperature. Toes-
Black-paintedsurface Aluminumshuter Emisivityz0.9
Fig.1. Schematicoftheexperimentalaparatusthatwasusedto measuretheemisivityofliquidpropanol.
timatethetherma1efectofthethermocouplebeadon temperaturereading，weusedthrediferent(25-， 50-，and75ボ m)wirediametertype-T(coperversus
Constantan)thermocouples. Whenthethermocou 回
p1eswereplacedonthe1iquidsurface，thethermo- coup1ewirewasextendedalongtheisothermonthe fue1surfacetominimizeheat10sthroughthewire andtoensuregoodcontactwiththe1iquidsurface duringmeasurement. Thesethrethermocoup1e readingsdiferslightlywhentheyareusedtomea-
surethesame1iquidtemperature: thesmalestdi
同
ameterthermocoup1egavethehighesttemperature reading，the1argestdiametergavethe10westtem- peraturereading，andthemediumdiameterreading registeredbetweenthetwo. Byap1yingasimple 1inearextrapo1ation，weobtainedthezerodiameter thermocoup1e reading，which indicates the actual liquid-surfacetemperature. Mterthiscalibration wascomp1eted，weusedon1ya50-μm-diameterther- mocoup1efortherestofthelneasurements. For eachthermocouplemeasurement，theefectofthe
thermocoup1ebeadwascorectedbytheabovecali
同
Figure2showstheexperimentalaparatusthatwas usedtomeasureIRabsorptionwithpropano1vapor.
IRcamera
Th巴rq∞upl巴
¥r- T1問
Fig.2. Schematicoftheexperimentalaparatusthatwasusedto measuretheIRabsorptionofpropanolvapor.
20August20/Vo.l39，No.24/APPLlEDOPTICS 4279