浙大现代热物理测试考试答案

1.PleasedescribetheprincipleoftheTunableDiodeLaserAbsorptionSpectroscopy(TDLAS)techniqueanditsadvantage.（FeiWang）TDLAStechniqueisusuallyusingtunablediodelaserwithasinglenarrowbandtoscanmeasuredgas,differentgasmoleculeshavedifferentabilityofabsorbinglaser.Thenwecouldgetdifferentgasmoleculesabsorptionlinefordifferentgas.Advantages：1.Nointerferencefromgasandparticles,2.Thelessresponsetime，lessthan1ms，real-timeandon-linemeasurementcanberealized3.Thelinewidthoflaserisabout15MHz(10-4nm),andtunablerangeis30GHz(0.2nm)4.Thedisturbanceofothergascanbeavoidedbyselectingnarrowgasabsorptionline(usuallylessthan10GHz)5.Thegasconcentrationaslowasppmorppblevelcanbemeasured6.Non-intrusiveandfiberoutputaresuitableforon-siteinstallationandfieldsmeasurement7.Nosamplingandpretreatment8.Averageresultsofline-of-sightIntraditionalway,gasisdetectedbythenon-dispersedinfraredgasanalyser.Theresultgetinthiswayisnotcredibleallthetime.Thetraditionalmethodgottheshotperiodofcalibration,longresponsetime.In-situdetectingisactuallyoutoftraditionalmethod’sreach.ThegasmonitoringsystembasedonTDLAScouldsolvealltheproblemsthattraditionalmethodhas.2.○1GeneralprincipleforvelocityandsizemeasurementbyPhaseDopplerAnemometry.SizeofcoalpowdercanbemeasuredbyPDA?Why?ORTheprincipleofvelocitymeasurementisthesameasthatusedinLaserDopplerVelocity.LDVisbasedonthephysicaleffectofMiescatteringThereforetheflowhastoseededwithparticlescapabletofollowtheflowsuchthattheirmovementreflectsthemotionoftheflowwell.TheLDVtechniqueisbasedontheprinciplethatlight,scatteredbyaparticlethatismovingrelativelytothelightsource,showsafrequencyshiftincomparisontothelightsourcewhichisreferredtotheDopplereffect.TheprincipleofthePDAisbasedontherelationshipbetweensphericalparticlesizeandthephasedifferenceofthetwoDopplersignals.PDAmakesuseofthefactthatscatteredlightwhichisreceivedfromtwodifferentdirectionsofobservationhasaphasedifference,whichisproportionaltothediameteroftheparticles.No，itcannot.Becausetheparticles(droplets,bubbles,solids)havetobespherical;otherwisethediameterandconsequentlythemassfluxcannotbedeterminedcorrectly.Generallythesizeoftheparticlescanbeintherangeofsomemicro-toseveralmillimeters,whichdependsontheopticalconfiguration.○2GeneralprincipleandrecentprogressofParticleimagevelocimetry?(GerardGrehan&XuechengWu)ThenameofPIVisself-explaining:ThevelocitydistributioninawholefieldofafluidflowisdeterminedbymeasuringthedisplacementsΔsthattheimageoftraceparticlesexperienceduringatimeintervalΔt.Thereforeinstantaneousvelocityvalues=Δs/Δtaremeasuredsimultaneouslyatmanypositions.Tracingparticlesareneededforlightweightandsmallenoughtofollowthefluid,havingexcellentscatteringcharacter.PIVis2Dmeasurement,out-of-platevelocityislostandunabletogetvelocityina3Dvolume.ExtensionofPIVtechnique3DscanningPIVitsremark:timedelayedmeasurement1)Scanningavolumetogetthedepthinformation2)Multipleframesrecordingandhigh-speedscannerarerequired3)Timelagbetweenframes:quasi-3Dmeasurement3DParticleTrackingVelocimetry(PTV)itsremark:lowresolution1)Extracting2Dparticlelocationsfromimagescapturedfromdifferentviews;2)Reconstructing3Dparticlelocationsaccordingtotheparametersofcamerasandcalibrationinformation;3)Tracking3Dparticlesinthevolumetogetthevelocity4)Extremelylowresolution(hundredsofvelocitymapinonevolume):cannotoverlapHolographicPIVitsremark:truevolumetricmeasurementwithhighresolutionNEWtrendsinPIVDual-planestereoscopic(立体）PIVsystem3Devaluationrequiresanumericalmodel,describinghowobjectsin3Dspacearemappedontothe2Dimageplaneofeachofthecameras。parametersforthenumericalmodelaredeterminedthroughcameracalibration。HighSpeedPIVsystem1solidstatelasers2highpulseenergy3CMOScameraswithhighsensitivity4Mega-pixelresolution@kHzrates5time-spacecorrelation6highervectorfieldresolution7higherordercorrelations(e.g.accelaration)withkHzratesMicroPIV1Volumeillumination(lightsheet,PIV)2Fluorescentmicrospheres(microspheres,PIV)HPIVitsremark:truevolumetricmeasurementwithhighresolutionCurrentsituation•Nocommercialproductavailable•Challenge–OpticalHPIV:Complicatedcomponents;timeresolvedreconstruction–DigitalHPIV:limitedmeasurementvolumeandspatialresolution;hugeamountofcalculation•Potential:true3C-3Dmeasurementtechnique•Potential:Extractalsotherefractiveindex3.Themathematicprincipleofalgebraicreconstructionmethod(QunxingHuang)重组Howcantomographybeusedforflametemperaturemeasurement?(QunxingHuang今年ppt上的题)4.Describeon-linemeasurementmethodsofPM2.5underhightemperatureenvironment(GerardGrehan,LinghongChen&YuqiJin)由于激光具有良好相关性,抗干扰能力强,能持续稳定地输出一段脉冲能量,基于激光光谱的检测技术以成为世界上燃烧研究的主流诊断方式,其中比较成熟的方法包括消光法(LightExtinction,LE)、激光诱导炽光法(LaserInducedIncandescence,Lll)、发射光谱法(EmissionSpectrum)4.GeneralprincipleandapplicationofLIFtechnologyinthecombustiondiagnosticarea.（Marcus&ZhihuaWang）网址=Zjz292l804_NVk-B6jOORB7OewTWmhR2-dCjWtqvq-PUSR6ACpkc0f9uo8iCtTKesDXfjGsAwe2lK8gF4OFa8kQTo6q5GadNk5smFlGwtKqPrinciple（原理）Application：(应用方面）Engineapplications（燃料和空气的混合情况测量）GasturbineapplicationsFurnace/bioapplicationsSpecialchallenges(应用时遇到的挑战，问题）Highp