Manual

4|Descriptionoffunction BÜCHILabortechnikAG
20/46 UltrasonicController
4.3 Dropsizedistribution
Fig.5:Dropsizedistribution
X Dropdiameter(microns) Y Percentofdropsbelowgivendi
ameter
1 Sautermeandiameter 2 Weightmeandiameter
3 Surfacemeandiameter 4 Numbermeandiameter
5 Numbermediandiameter
Dropsizeinanultrasonicallyproducedsprayisgovernedbythefrequencyat
whichthenozzlevibrates,andbythesurfacetensionanddensityoftheliquid
beingatomized.However,frequencyisthepredominantfactor.Mediandrop
sizeisinverselyproportionaltofrequencytothe2/3power.Thus,thehigherthe
frequencythesmallerthemediandropsize.
Typically,thedropsizedistributionfromultrasonicnozzlesfollowsalognormal
distributioncurve.Insimpleterms,thisdistributionhasthefamiliarbellshape
butonalogarithmicscale.Thechartshowsthisdistributiononacumulativeba
sisforseveralnozzlefrequenciesforwater.
Variousparameterscanbeusedtocharacterizethemeanandmediandrop
sizeofaparticulardropdistribution.Thenumbermediandiameterdefinesthe
50%pointindropsize–thatis,onehalfofthenumberofdropsinthespray
havediameterslargerthanthisvaluewhiletheotherhalfhavediameters
smallerthanthisvalue.Thenumbermeanandweightmeandiametersareav
eragediameters.Thenumbermeandiameterisobtainedbyaddingtogether
thediameterofeachdropinaspraysampleanddividingthatsumbythenum