Page 95 - konishipaper

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r_-
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二五三 . .心 ‘- ふ ; ¥ - よ い ム ム い い よ し 1)
of 2 m m thicknes s. The trays were divided in two compartmentsbyapartitionthatwasplacedat13ofthe lengthofthetray.Thepartitionwasdesignedtosep訂 ate thetwoliquidsfromeachotherexceptattheswfaceas showninfigure1. Thissituationwilsimulatethereal f1amespreadingcaseinwhichtheflamewil heatthe liquidatsurfaceonly. Thenduetotheswfacetension and buoyancy di百erence this hot liquid starts to move forwardanddownward，andmixingwiththedownstream cold liquid. Figure 2 shows the flame's leading edge movement along the center line of the tray on the fuel swfaces.
Y Liquis2
SideView
X
Figure1Schematicdiagramofflamespreadaparatus.
Figure2A photographshowingtheflamespreadover トpropanolpooledinaPyrextray(5m mwide).
1-propanol and 1-butanol alcohols were used in this studyasliquidfuelsbecausemuchresearchhasbendone using.this fuel，for example，NASA's microgravity programandItogroupinJapan[6，7，9，10，1，12]. This provideduswithagood databaseforcomparison. Iso- Octane was chosen to be mixed with the two alcohols becauseofitssurfacetensionpropertiesthatmatchclosely t h e p r o p e r t i e s o f l - b u t a n o l a n d 1 - p r o p a n o l at 2 S o C h i g h e r thantheroomtemperature.
Table 1 shows surface-tension values for the liquids used in this study. It is wel known that as the tempera旬 reincreasesthesurfacetensiondecreases. Inthe
Iso~octane
寸討す討す可討究開守守男宗宗宗宗弔問
case offlame spreading ，the 1fame heated up the liquid beneathitwhichreducedthesurfacetensionandgeneratea forcecaledthesurfacetensionforce. Thisforceexpeled thehotliquid仕ombeneaththef1ame，therebydisplacing thecolersurfacelaye.r
Table1Surfacetensionvaluesoftheliquidsusedinthis study
Swface Tension dynes/cm Tempera旬rel-propanol I-butanol Iso-octanewater
。C
10 24.48 26.28 73.5 20 23.78 24.6 72.74 25 23.32 24.93 21.14 71.97 50 21.38 2.69 67.91 75 ーーーーーーー 20.44 ー田ーー
ResultsandDiscusion
T h e m 可 o r h e a t - t r a n s f e r p r o c e s s b e t w e e n t h e f1 a m e ' s leading edge and the liquid is a highly transient phenomenoninvolvingbothliquidandgasphases.
Inthisstudywesimulatedtheliquid-heat-conv~ction f10w experimentaly by sudenly.mixing two iIquids， each having di百erent tempera加 re and surface-tension properties. Thefirstliquid(iso-octane)simulatedthe heatedliquidbeneaththef1ameathigh temperatureand lowsurfacetension. Thesecondone(1-propanolorト butanol)simulatedtheunburnedupstreamliquidat.room tempera加reandhighswfacetension. Bothliquidswere mixedsudenlythroughthesurfaceonly
has swface tension.value at room tempera旬 re similar to that for l-propanol or.l-butanol whentheflameheatedthemuptoaround2SoChigher. ln figure 1， area 1 was fiUed with iso-octane se eded with
aluminum particles and area 2 was fil led with either ト propanoIor 1-butano.l Suddenly both liquids were mixed.togetheratthesurfaceforaboutfewminutes. A thin lasershetwasusedto iluminatetheparticlesas theytransferfromarea1toarea2. A highresolution videocameraconectedtoacomputerthroughacapturing boardwasusedtorecordtheprofile'simages.
Figures 3，4 show images ofLSTP top views of mixing Iso-Octane with 1-butanol and l-propanol respectivelyina5mmwidetray. Theparticlesinthe iso-octaneweremoving合omrightto leftin atwin vortices profile. .The side view in figure 6 shows large circulation aheadofthepartition. This type of 1f0w loksvelysimilartotheoneof flamespreadingover liquidinfigure5.
Inthe real case the flame began to propagate，the preheatedregionextendedaheadofthe f1ame. Itthen developedtwosymmetricvorticeswhichroleduptoward thesidewalswhi1ethepreheatedliquid at the center c o n t i n u e d t o p r o c e e d u p s t r e a m o f t h e f1 a m e a s s h o w n i n figures5and8.Later，whenthegaseousfuel-airmixture overtheliquidsurfacereachestheleanflamabilityiImit，
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