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1、SurfaceRoughnessandItsEffectsm.R.PaisontheHeatTransferMechanismL.C.ChowinSprayCoolingDepartmentofMechanicalEngineering,Inthespraycoolingofaheatedsurface,variationsinthesurfacetextureinfluenceUniversityof.Kentucky,theflowfield,alteringthemaximumliquidfilmthickn
2、ess,thebubblediameter,Lexington,KY40506vaporentrapment,bubbledeparturecharacteristics,andtheabilitytotransferheat.Anewmethodfordetermininganddesignatingthesurfacetextureisproposed,andE.T.Maheikeytheeffectsofsurfaceroughnessonevaporation/nucleationinthespraycoo
3、lingflowfieldstudied.Aone-dimensionalFourieranalysisisappliedtodetermineexperi•AeroPropulsionandPowerLaboratory,WrightResearchandDevelopmentCenter,mentallythesurfaceprofileofasurfacepolishedwithemerypapercoveringaWright-PattersonAirForceBase,OH45433spectrumofg
4、ritsizesbetween0.3to22fim.Heattransfermeasurementsforliquidflowratesbetween1to5l/handairflowratesbetween0.1to0.4l/sarepresented.Maximumheatfluxesof1200W/cm2forthe0.3x.msurfaceatverylowsuperheatswereobtained.IntroductionCurrentheattransferenhancementresearchha
5、sbeendi•contactwithitsvaporatbutonepressure,itsvaporpressure.rectedtowardphase-changeprocesses.SuchprocessestakeIfbysomemeansthevaporpressureisreducedintheim•advantageofthefactthatapuresubstancewillabsorbormediatevicinityofthesurface,thenthephasechangetem•rele
6、aseheatduringphasechangeatafixedtemperature.Theperaturewillalsodecrease.Inthecaseofwater,fora30percentexchangeofthislatentheatisfeasibleatlowdegreesofsu•decreaseinvaporpressure,thephase-changetemperatureisperheat,anddependingonthesubstance,themagnitudecanreduc
7、edby10percent(Mark's,1978).befargreaterthanthecorrespondingsensibleheatexchangeAnair/dropletimpingementflowfieldonthesurfacepro•forthesametemperaturedifference.ducedbyanairatomizingnozzleisillustratedinFig.1.TheIntheconventionalmethodsofforcedconvectiveandra•a
8、irjetonimpingingthesurfaceformsastagnationpointflowdiativeheattransfer,highheatfluxescanbeachieved.How•field.Thedropsdonotfollowtheairstreamlinesclosetotheever,suchmodesentailexces
