ASHRAE.CH-03-13-2-2003 Heat Transfer and Pressure Drop for Condensation

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1、CH-03-13-2HeatTransferandPressureDropforCondensationofRefrigerantR-404AatNear-CriticalPressuresYirongJiangSrinivasGarimella,Ph.D.StudentMemberASHRAEMemberASHRAEABSTRACTrefrigerantblendsatsuchnear-criticalpressuresisnotwellunderstood.Whileitisknownthatheattransfercoeff

2、icientsThispaperpresentstheresultsofanexperimentalstudyonandpressuredropinconvectivecondensationarestrongfunc-heattransferandpressuredropduringcondensationofrefrig-tionsofvaporquality,fewpredictivemethodsarereportedinerantR-404Ainsideahorizontal9.4mmI.D.tube.Theexper-

3、theliteratureforrefrigerantblendsatnear-criticalpressures.imentswereconductedatnominalpressuresof80%and90%ThispaperpresentstheresultsofanexperimentalstudyonofthecriticalpressureofR-404A.Anoveltechniquethatheattransferandpressuredropduringcondensationofrefrig-addresses

4、theconflictingrequirementsimposedbytheneedforerantR-404Ainsideahorizontal9.4mmI.D.tube.accuratemeasurementoflowheattransferratesforthesmallCondensationinsidehorizontaltubeshastypicallybeenqualityincrements,anddelineationofthetube-sideheattrans-treatedasbeinggovernedby

5、acombinationofgravityforcesfercoefficientfromtheoverallresistance,wasdeveloped.andinterfacialshearstresses,therelativecontributionsofLocalheattransfercoefficientsandpressuredropswere2whichchangewiththegeometryandfluidconditions(formeasuredforthemassfluxrange200

6、g/m-sinsmallerdiametertubes,surfacetensionforcesalsoplayansmallqualityincrementsovertheentirevapor-liquidregion,increasingrole,asdemonstratedbyColemanandGarimellaspanningseveraldifferenttwo-phaseflowregimes.Thesedata[2000a,2000b]).Whiletheannularflowpatternisassociate

7、dwerecomparedwithexistingcorrelationsforcondensationwithhighvaporshearstresses,stratifyingandwavyflowsheattransfertoassessthevalidityofthesemodelsforthishigh-appearwhengravityforcesdominate.Manyofthewidelypressurerefrigerantblendwhenoperatingnearthecriticalusedcondens

8、ationheattransfercorrelations(forexample,pressure.ThehighreducedpressuresinthisstudyresultinthosebyTravissetal.[1973]andShah