Page 75 - konishipaper
P. 75
吋ぜ
AkihikoIto OitaUniversity
TadashiKonishi OitaUniversity
ABSTRACT Werecentlydevelopedtwodiferentopticaltechniquesinorder
to.simu1taneously measure transient.2・D profiles of'velocity， temperature and fuel concentration that were generated by a spreadingflameoverliquidfuels. Onetechniqueemploysaparticle- tracksystemcombinedwithalaser-shetsystem(PTLS)andahigh sp回 dcamera，whiletheothertechniqueemploysadualwavelength holographicinterferometry(DWHI). 官lep1工S systemrevealed transient2・D]?rofilesofflameinducedflow，whileDWHIrevealed 2-Dprofilesoffuelconcentrationoverliquids. Inthispaperwe presentaseriesofvelocityprofi1esforapulsatingflamespreaqover propanolandconcentrationprofi1esforgaseouspropanoldeteロnined withP1LSandDWHIrespectively.Othetresearchershavepred.icted theformationofsma1twincirculations，oneagas-phasecirculation
justaheadoftheflame'sleadingedge，andtheotherasmalliquid circulationjustunderneaththegas-phasecirculation. OurPTLS results confirmed'these predictions，.ie.，the formation of5・10 milimeterdiametercirculatiQninthegasphaseandanacompanying aproximately20milimeterdiameterliquidcirculation. Basedon these data，we ofer a phenomenologica1 expl加 ation of the mechanismofpulsatingflamespread. Inadition，weshowthat DWHIisaverypromisingtechniqueformeasurlngtr佃 sient釦el- concen釘ationprofilesoverliquids.
INTRODUCTION HistoricalBackaround
百lephenomenonofflamespreadoverliquidsisofc沼 町 四t interestbecauseofitsimportanceωfiresafety. Ourobj巴ctiveis diferen.tWewishtolearnmoreaboutthefundamenta1mechanism oftheflamespread. Anexcel1entreviewoftheliteratureonthis problem was published by Ros s [19 94] and Hirano and Suzuki [193]andthetheoretiCa1backgroundoftheproblemwasprovided byWiliams[1985]. 官leyadresedmanyoftheproblemsthat nededto'beinvestigated.
百lepresentpaperisacontinuationofourpreviousstudieson flamespreadoverliquids[Ito，Masuda，Saito，191;Ito，Saito，叩d Cremers，195;'andTashtoush，Narumi，Ito，Saito，andCremers， 196].Inぬeses旬diesweapliedholographicinterferometry(HI)旬 obtainadetailedandinstantaneoustemperaturedistributioninthe
HTD.Vol.352，ProceedingsoftheASMEHoatTransferDivision Volume2 ASME1997
THEMEASUREMENTOFTRANSIENT2・DPROFILESOF VELOCITVANDFUELCONCENTRATIONOVERUQUIDS
.， ..
141
ー‘
‘
•1: ，
‘ .
h 、 ，
e
AkiraNarumi KanagawaInstituteofTechnologγ
GassanTashtoush，KozoSaito， andClifordJ.Cremers UniversityofKentucky
liquidphasene紅 白efueIsurface. Ineachofmethanol，ethanoIand propanolwefoundsubsurface-liqu~d conv即位oninboththeuniform spread，andpuIsatingspreadregions.Tounderstandthemechanisms offlamespreadinbothr~gions， researcherstriedtoidenti勿 印 刷uor heat-transferprocesbetwentheflame'sIeadingedgeandtheliquid， whetheritocursthroughthegasphase"liquidph出 eorboth.When theliquiqconvectionisproducedandittravelsaheadoftheflame's leading'edge，theflamespreadislikelytobecontroledbyitbecause the convection car ries the high temperaωre liquid ahead of the flame'sleading凶ge. This.enhancesevaporationofliquidvapor resultingintheformationofaflamablemixtureoffuelandair throughwhichtheflamecanspread. Ifthereisnoliquidconvection aheadofthefl仰 向 1eadingedge，themajorheattransferCalocur
betwertheflame'sleadingedgeandtheliquidbyc<;mductionand radiationinthegasphase，becauseconductionthroughtheliquidis negligible[GlasmanandDryer，1981].
Liquidconvectionisuniquetoflamespreadoverliquidsandit complicatesthespreadingprocesincomparisontoflamespread oversolids，whichhavenocondensedphaseconvection[Wiliams， 1985]. 古川s，itisimportanttQmeasuretempera加reandvelocity profilesintheliquidphase. Akita[1972]wasthefirstresearcherto aplyashadowgraphtechniquetovisua1izetheliquidconvection. Hereportedthe.formationofliquidconvectioriinthepulsating region，butnoliquidconvectionintheuniformspreadregion.Based on Akita's data，Glas sman and Dryer [1981] proposed that the uniformspreadiscontroledbyheatconductionth:roughthegas
phase，whiIeinthepulsatingregiontheliquidconvectionplaysan importantrole. However，theproposedIl).echanismfortheuniform spreadisquestionable，b巴causethegas-phaseconductionmaynot transfersuficientheatfortheflametospreadatarateofnearly10 cmls.
To， solve this problem買 we developed 佃 HI system and performedthetr釦 sientmeasurementofliquidtemperaωre[Ito， Masuda，andSaito，'191]. 百leresponsetimeofourHIsystemis les s than 1 micro second. W e estimate the uncertainty of the spatia1 resolution to be ま 0.1 m m，and the tempera加 re resolution to be 土 0.1 oc[lto，Masuda，andSaito，191]. Usingthemsystem，we observedalargeliquidconvectionbothintheuniformandpuIsating spreadregions. TheiIquidconvectionintheuniformspreadr，
-
