fluid flow 4

7/28/2019 Fluid Flow 4

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FLUID FLOW

Cyclone SeparatorsAsst.Prof.Dr. Sirirat Wacharawichanantsst.Prof.Dr. Sirirat Wacharawichanant

Department of Chemical EngineeringFaculty of Engineering and Industrial Technology

Cyclone SeparatorFor separation of small solid particlesor mist from gases, the most usedtype of equipment is cyclonese arator..

A device that uses centrifugal forcesto accelerate the settling of solidparticles.

Basically, a particle-laden gas streamis introduced tangentially in the unit.

Particles move to the cycloneseparator walls and then to the

FLUID FLOW : DEPARTMENT OF CHEMICAL ENGINEERING

bottom of the device.The gas first moves downward, thenup to the top.

Cyclone Separator(Continue)

The cyclone consists of avertical cylinder with a conicalbottom.

-enters in a tangential inletnear the top.

This gas-solid mixtures entersin a rotating motion, andvortex formed developscentrifugal force, which throwthe particles radially toward


Fig. 7-1 Gas-solid cyclone separator.

e wa .

On entering, the air in cycloneflows downward in a spiral orvortex adjacent to the wall.

Cyclone SeparatorWhen air reaches near thebottom of cone, it spiralupward in a smaller spiral inthe center of cone and

(Continue)

cylinder.

A double vortex is present.

The downward and upwardspirals are in the samedirection.

The particles are throwntoward the wall and falldownward leavin out the


,bottom of cone.

A cyclone is settling device inwhich the outward force on theparticles at high tangentialvelocities is many times theforce of gravity.


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Theory for Cyclone SeparatorIt is assumed that particles on entering a cyclone quicklyreach their terminal settling velocities. Particle sizes areusuall so small that Stokes law is considered valid. Forcentrifugal motion, the terminal radial velocity vtR is givenby Eq.(4-1), with vtR being used for vt,

18

rDv

p2p

2

t

(4-1)

( )22


: vtan/r

vtan : Tangential velocity of particle at radius r

(4-2)

18

v ppRt

Theory for Cyclone SeparatorEq.(4-2) becomes

vv

vDv

2tan

t

2tanp

2p

tR

(4-3)

(Continue)

grg

The higher vt, the greater vtR and the easier it should be tosettle the particle at walls. However, the evaluation ofradical velocity is difficult, since it is a function of vt, vtan,and position radially and axially in cyclone. Hence, thefollowing empirical equation if often used.


B1,n :Empirical constants.

(4-4) n

p2p1

Rtr18

Dbv

Cyclone Separator





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fluid flow 4

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