ASHRAE.4503-2002 A Numerical Study of Pressure Distribution and Flow

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1、4503ANumericalStudyofPressureDistributionandFlowthroughRigidShort-TubeOrificesRamadanBassiouny,Ph.D.DennisL.O’Neal,Ph.D.,P.E.FellowASHRAEABSTRACTFlowcharacteristicsthroughrigidshort-tubeorificeshavebeendiscussedbypreviousresearchers,(Baily1951;Afiniteeleme

2、ntmodelwasusedtoestimatethepressureZaloudek1963;HenryandFauske1971;AaronandDoman-distributioninsideashort-tubeorificeandmassflowforski1990;Kim1993;KimandO’Neal1994a).Mostofthesesingle-phaseflowofR-22andR-134a.Theresultsfortheresearchershavereportedthatflow

3、insideashorttubewasnumericalmodelwerecomparedtopublishedexperimentalmetastable.Thismetastabilitywascharacterizedbyafailuredata.Thestudyincludedthreedifferentlength-to-diameterofthetwo-phasemixturetoattainequilibriumintheshort-(L/D)ratiosandupstreampressure

4、srangingfrom1.45totubeduetorapiddepressurization(Zaloudek1963).1.72MPaforR-22andfrom0.9to1.17MPaforR-134a.Downstreampressuresrangedfrom1to1.36MPaforR-Mei(1982)presentedasemi-empiricalmodeltocalculate22andfrom0.6to0.86MPaforR-134a.Aconstantsubcoolingthemass

5、flowrateforliquidsubcoolingequalto22.2ºCorof13.9ºCwasusedforallcases.less.However,forsubcoolinghigherthan22.2ºC,heintro-ducedamodifiedchokingmodel.TheuseofthesetwomodelsPressuredistributionresultsfromthenumericalmodelwasapplicableintherange7.5

6、wedcloseagreementwiththeexperimentaldataforR-22.Moreover,withR-134a,themodeltendedtooverpredicttheKimandO’Neal(1994b)developedasemi-empiricalpressurerecoveryafterthevena-contractawhenthedown-correlationtopredictthemassflowratebeforetheflashingstreampressur

7、ewasveryclosetothesaturationpressure.Thepointasafunctionofboththeupstreamandsaturationpres-numericalmodelcapturedtheexpectedsharpdropinpressuresures.Theyfoundthatthereductioninthedownstreampres-atthetubeinlet.Formassflow,themodelwaswithin7%ofthesurecauseda

8、correspondingreductioninthedownstreampublishedexperimentaldataforbothR-22andR-134a.temperaturesduetothefactthatthedownstreamwassatu-rated.Consequently,theheattransferalongthetubewouldINTRODUCTIONdelaytheonset