cyclone separater
TRANSCRIPT
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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