辐射换热计算部分The heat transfer calculation sectionWord下载.docx
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辐射换热计算部分The heat transfer calculation sectionWord下载.docx
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Heattransfercalculationpart
First,thebasicconceptsmainlyinclude:
thedefinitionandnatureoftheAnglecoefficient;
Thecharacteristicsofradiationheattransferonthesurfaceofthegraysurface;
Theprincipleandapplicationoftheheat-shieldplate;
Gasradiationandsolarradiation,etc.1,brieflydescribestheradiationheatexchangenetworkofaclosedspace.A:
solvingradiationinparwithelectricalthermaldissipationofohm'
slaw,itisconcludedthataclosedcavitynetwork.
Thecalculationformulaofradiantheattransferbetweenthetwosurfaceofthetwoblackbodies:
Eb1minusEb2isthepotentialdifference,
Theequivalentresistance,calledspacethermalresistance;
Anetradiationheattransferformulabetweenthesurfaceofthegraysurface:
Intheformula(eb1-eb2)isequivalenttothepotentialdifference,
Theequivalentresistance,calledsurfacethermalresistance.
Concretestepsasfollows:
firstofall,allsurfacesmustformaclosedsystem,andthenmapthermalresistancenetwork,thespecificmethodis:
(1)everyobjectsurfaceforanode(thesurfaceoftheobjectshouldbewiththesametemperatureandthesurfaceradiationabsorptioncharacteristics),itsthermalpotentialforeffectiveradiationJi;
Acorrespondingspacethermalresistanceisconnectedtoeachofthetwosurfaces;
Asurfacethermalresistanceand"
battery"
(blackbodyradiationEb)areconnectedtoeachsurfaceandground.IfthecoefficientoftheAngleis0,thespaceheatresistancegoestoinfinity,thenthecorrespondingtwosurfacescanbedisconnectedandnotconnectedtotheheatresistanceofthespace.5]ifasurfaceisadiabatic,itspotentialforfloatingheat,notconnectedtoground.2,theblackbodycomparedwithheavyradiationsurface,thesurfacehastheJ=Eb.Doesthismeanthattheblackbodysurfaceandaradiatingsurfacewiththesameproperties?
Answer:
althoughtheblackbodyheavyradiatingsurfaceandthesurfacehasthecharacteristicsofJ=Eb,butbothhavedifferentnature.Onthesurfaceoftheblackbodytemperaturedoesnotdependonotherparticipatinginthesurfaceoftheequivalentofthesourceheat.Andthetemperatureoftheradiatingsurfaceisfloating,basedontheothersurfaceofradiation.
3,shouldstrengthentheradiationheattransferbetweenobjects,someoneputforwardusingemissivityepsilonmaterials.Andaccordingtothekirchhoff'
slaw,epsilon=alphatodiffusegraysurface,theemissivityoftheobjectanditsabsorptionrate.Somepeopletoconcludethat:
withincreasingtheemissivityofepsilonmethodcannotenhancetheradiationheattransfer.Pleasejudgethecorrectnessofthisstatement,andexplainthereasons.
A:
whenotherconditionsareunchanged,thesurfacethermalresistanceoftheobjectcanenhanceradiativeheattransfer.Therefore,theabovestatementisincorrect.
Itcanbeseenthatwhentheepsilonislarger,thesurfaceradiatingresistanceoftheobjectissmaller,thus
4,asshowninthefigure,soakedingreyconcentricsphericalshellsisinsertedbetweentwoconcentricradiationheatsphericalshell,havecoveredheatsphericalshelloutersphericalshellwithinornearsphericalshells,sphericalshellsandsphericalshells12surfaceradiationbetweenthegreatertheheat?
A:
theradiationnetworkmapoftheradiantheattransfersystemisshowninthefigurebelow.
Obviously,thethermalresistanceR1,R2,R5andR6inthediagramwillremainthesamewhenthediameteroftheheat-shieldingsphericalshellchanges,butR3=R4=increasesanddecreases.Therefore,thelargertheradiativeheatiswhentheshellisclosetotheoutershell,thelargertheradiusis.
Withtheradiusoftheshell
5.Whatarethecharacteristicsofgasradiation?
1)differentgaseshavedifferentradiationandabsorptioncharacteristics.
Onlypartialgashasradiationandabsorptioncapacity;
2)hastheabilityofradiationandgasabsorptionwavelengthselective,suchasCO2,H2Ohasitsthreeband-discretespectrum.3)radiationandabsorptioninthewholevolume.6,solarcollectorheat-absorbingsurfaceitisadvisabletochooseinthenatureofwhatmaterial?
Whyisthat?
solarcollectorisusedtoabsorbsolarradiation,thusthesurfaceshouldbeabletoprojecttomaximizetheabsorptionofsolarradiation,andguaranteetheheatdolessatthesametimeislost,oraslittleaspossibleonthesurfaceofradiantenergyoutward.Butthesunradiationisheatradiation,theradiationenergyismainlysettoshortwavespectrum(suchasvisiblelight),collectoritselfislowtemperatureradiation,radiat
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