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CycloneSeparators

Physicsbehind

them

and

how

they

work

SebastianBENAVIDES

Specialization Course

December 2012

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How

they

are

composedWhat

happens

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Velocitydistribution

inside

theCyclone

Canbeexplainedthrough

Axial

Radial

Tangential

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Velocitydistributionon

hydrocyclones withafree

vortex

Axial Radial Tangential

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Tangential Radial Axial

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Equilibriumbetweencentrifugalforceandradial

pressure

gradient

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Pressurefield

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Commonassumptionstointerpretandunderstand

whathappens

inside

the

cyclone

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Radialmotion

Complicated.

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F_C=F_D

4/3*rho_p*pi*r^2*v_t^2

=6*pi*mu*r*v_r

v_t^2/r=9/2mu*v_r*1/(r^2rho_p)

Foru_terminal =d^2*g*rho_p/(18*mu)

u_terminal =(r*g*v_r)/v_t^2

Forseparationatd=0.4d_owhered_o istheoutletdiameter.

u_terminal =0,2*(d_o*g*v_r)/v_t^2

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Efficiency TheyresultfromintegratingEq.Cyclonefordifferentflowsituationsand

hypothesis.TheycalculateX50.X50correspondstotheparticlewhosetimeequalstheresidencetimeofthegasandisconsideredastohaveaseparationefficiencyof50%

Itis

assumed

that

aparticle

that

reaches

the

wall

gets

separated.

Even

more

so

for

particleswhointhetimeittakes,shouldvereachedagreaterradialdistance.

Timeofflightmodel

Notionofequilibriumorbit(CS/controlsurfaceequaltozero/Barth)

Gradeefficiency

Overflow,Underflow

Lowcutoff, highefficiency(oil/water)

Lowresidence

time

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Formulasfor

cyclone

efficiency

Theyperformwellforlowvaluesofsolidloadings(

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Natural

turning

length

L_n

Turninglength

Naturallength

Vortexlength

Axisymmetric onlyatlowvelocities,athighwallfrictioncoefficientsatlowswirl.

DecreaseofcycloneefficiencybyreducingL_n,staticwallpressureandtangentialvelocitymeasurements

Reason:vortexisanunstablestructure.Itoscillatesradially atanyaxiallocation(PVCPrecessing VortexCore).Whataninstabilitydoesistomakethevortexbendandendonthewallinsteadmakingtheseparatorloseefficiency

Betterfor

L_n