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Themajorportionofthisaparatusisesentialythe sameaswhatweusedinourpreviousstudieson 丑amesspreadovera丑ammab1eliquid.7 ThePyrex- madefue1trayis20m mwideX 30m mdepX 160 mm10ng. Asolidcoper50-mm-diameter，50-mm- thickcy1inderb10ckwasusedastheb1ackbodyradi- antsource. Thesurfaceofthecopercy1inderhasa smoothmachinefinishandwaspaintedwithaflat b1ackpaint. Thepainthasahighcarboncontent andwithstandsasmuchas300oCwithout10singits initia1b1ackbodyquality(themanufaCturerdeter- minedtheemisivitytobegreaterthan0.9)，and thusisthebestpaintforourmeasurements. With theexceptionoftheb1ack-paintedsurface，thecoper cy1inderb10ckwaswrappedwithheatertapeand thencoveredwithafiberg1asheatinsulator. Two thermocoup1eswereembeddedinthecopercy1inder at2and5m mfromthesurfacebydriling五neho1es attheback. Eachthermocoup1ewasinsertedintoa ho1e，thebeadwaspresedtotheexact10cationofthe coperho1esurface，andtheho1ewasfiledwithheat- resistinggluetosecuregoodphysica1contactwiththe copercylinderduringtheexperiment.
Mterthee1ectricheaterwasturnedon，ittok ap proximate1y 1 h for the two thermocoup1es to
104
s
6 5E53103
，〈3。gfOコF102
1。 10
l-propanol
5 10 15 Wavelengthλ(μm)
statetemperaturereading. When thesteadystatewasachieved，thesurfacetempera-
tureofthecopercylinderwasdeterminedbylinear extrapo1ationofthesetwothermocouplereadings.
Atthispoint，theopentopsurfaceoftheliquidtray wascoveredbyana1uminump1atesothatnopropa- nolvaporcouldbere1easedbetweentheIRcamera andtheblackbodysource(b1ack-paintedcopercyl- inder). 恒 1eIRcamerareadtheblackbody(greater than0.9emisivity)surfacetemperaturethrough air;theIRtemperaturewasadjustedtobethesame asthatofthesurfacetemperature. Next，thealu- minumcoverwasremoved，andthepropano1vapor wasreleased. Duringthisperiod，七heblackbody surfacetemperatureremainedthesame，andtheIR camerathatcontinuouslymonitoredtheblackbody surfacetemperaturebegantoshowa10wertemper- aturereading. Thetemperaturecontinuedtode-
日g.3.Absor下tioncoe伍 cientofl-propanolasafunctionofwave- length.
tionofposition，asinthecaseofauniformmedia， then
I、
云=exp(αλhz)， (1)
whereαλistheabsorptioncoef五cientofthe1iquid， whichgeneralyvariessignificant1ywithwavelength andoftenvariessubstantialywithtemperatureand presure. Considerableeforthasbeenmadetode- terminetheabsorptioncoeficientforvariousgases， liquids，andsolids. Figure3showstheabsorption coeficientof1-propano1at23oCand1atmasafunc- tionofwavelength9; strongabsorptionpeaksare shownatcertainwavelengths. Figure4showsthe transmisiγityof1-propanol，estimatedfromFig.3，
λmaxT=2897.8μmK， (2) themaximumwave1engthisexpectedtobe企om8.4
to9.9μminthe20-7000temperaturerange. In
回
asmuchastheminimumliquidthicknesatwhich transmisivitybecomes1%is150μminthe8.4-
achieveasteady
回
crease until the propanol vapor reachedasteadystateandtheIRreadingreach~d a constantvalue. Atthispoint，thereisanestab- lishedtemperaturediferencebetweentheIRandthe b1ackbodythermocouplereadingsresultingfromIR absorptionwithpropanolvapor
3. TheoreticalConsiderations
A. InfraredAbsorptionbyLiquidPropanol
Wediscusspectra1radiationofintensity10λincident normalyonaliquidfilmofthicknesh z• Asthe radiationpasesthroughhz，itsintensityisreducedto 1A byabsorptionandscatering. Whenscateringis negligib1eandtheabsorptioncoeficientisnotafunc-
4280 APLlEDOPTICS/Vo.l39，No.24/20August20
concentration
‘
伺
forvariouswave1ength
thickneshz. ByuseoftheWiendisplacement1aw，
S10-1
b
〉
ω
A.=1，12
_~___~，!o_=:~_
，
←
λ(μm)
Fi1m Thicknes s h(μm)
2
~ 10-~---\--~一一一一一一_ c/.l
g
1-<
sasafunctionofliquidfi1m
‘
=8 A.=9
10-3
0 50 10 150 20 250
Fig.4. Changeoftransmisivityasafunctionof白 血 thicknesfor fivewavelengths.
λ