Cyclone Separator
Theory:
Cyclone separators or simply cyclones are separation devices that use the principle of inertia to remove particular matter from flue gases. Cyclone separators is one of many air pollution control device known as precleaners since they generally remove larger pieces of particulate matter. This prevents finer filtration methods from having to deal with large, more abrasive particles later on.
Working:
Cyclone separators work much like a centrifuge , but with a continuous feed of dirty air. In a cyclone separator, dirty flue gas is fed into a chamber. The inside of the chamber creates a spiral vortex, similar to a tornado.The lighter components of this gas have less inertia, so it is easier for them to be influenced by the vortex and travel up it.Cyclone separators are generally able to remove somewhere between 50-99% of all particulate matter in flue gas.
LAPPLE MODEL
Lapple (1951) model was developed based on force balance
without considering the flow resistance. Lapple assumed that a
particle entering the cyclone is evenly distributed across the
inlet opening. The particle that travels from inlet half width to
the wall in the cyclone is collected with 50% efficiency
The efficiency of collection of any size of particle is given by
KOCH AND LICHT MODEL
Koch and Licht (1977) collection theory recognized theinherently turbulent nature of cyclones and the distribution ofgas residence times within the cyclone. Koch and Lichtdescribe particle motion in the entry and collection regionswith the additional following assumptions:
• The tangential velocity of a particle is equal to the tangential
velocity of the gas flow, i.e. there is no slip in the tangential
direction between the particle and the gas.
• The tangential velocity is related to the radius of cyclone by:
uRn = constant.
LI AND WANG MODEL
The Li and Wang (1989) model includes particle bounce orre-entrainment and turbulent diffusion at the cyclone wall. Atwo-dimensional analytical expression of particle distribution
in the cyclone is obtained. Li and Wang model was developedbased on the following assumptions:
• The radial particle velocity and the radial concentration
profile are not constant, for uncollected particles within the
cyclones.
• Boundary conditions with the consideration of turbulent
diffusion coefficient and particle bounce re-entrainment on
the cyclone wall
IOZIA AND LEITH MODEL
Iozia and Leith (1990) logistic model is a modified version of Barth (1956) model which is developed based on force balance. The model assumes that a particle carried by the
vortex endures the influence of two forces: a centrifugal force,Z, and a flow resistance, W. Core length, zc, and core diameter,dc
Task:
Perform an analysis on the given cyclone separator model and apply four different boundary condition types at the inlet i.e. reflect, trap, escape and wall-jet and submit images on your findings on the different conditions.
Geometry:
The geometry was obtained by volume extraction from the assembly provided and single inlet and outlets were assigned
Meshing:
Considering element count 10mm size was selected with method set to tetrahedron
Discrete phase Boundary condition set to reflect.
Boundary condition :
Dia of discrete particle 5e-6m
inlet velocity:3m/s
velocity of flow :3m/s
k-epsilon model was used
Contours:
Velocity:
Particle time:
Most of the paricles escape efficiently .
Vortex:
Based on particular design vortex generation
Result:
We can understand the particle nature inside the cyclone seperator were we understand particles that got trapped and numer of them which escaped
Discrete phase Boundary condition set to escape
Velocity:
Vortex:
Particle time:
Result:
We can understand the particle nature inside the cyclone seperator were we understand particles that got trapped and numer of them which escaped
Discrete phase Boundary condition set to trap
Velocity:
Vortex:
Particle time:
Result:
We can understand the particle nature inside the cyclone seperator were we understand particles that got trapped and numer of them which escaped
Discrete phase Boundary condition set to wall-jet
Velocity:
vortex:
Particle time:
Result:
We can understand the particle nature inside the cyclone seperator were we understand particles that got trapped and numer of them which escaped
DPM ITERATION Reflect Escape Trap Wall-jet
Number tracked 364 364 364 364
Escape 330 328 328 328
aborted 0 0 0 0
trapped 0 0 0 0
incomplete 34 36 36 36
3.Vary the number of particles through the inlet and run the simulation for 3 cases. Report the number of particles that pass through or remain in the cyclonic separator. Post images to show the same. For this question, use the “Reflect” option as the boundary condition for the Discrete Phase
Case1 :
Meshing:
For this we\'ve set the overall meshing as 15mm (without adaptive mesh refinement )
Velocity:
vortex:
Particle time:
Result:
We can understand the particle nature inside the cyclone seperator were we understand particles that got trapped and numer of them which escaped
Case 2:
Meshing size se to 10mm
Velocity:
vortex:
Particle time:
Result:
We can understand the particle nature inside the cyclone seperator were we understand particles that got trapped and numer of them which escaped
Case 3:
Mesh size was set to 12mm
Velocity:
Vortex:
Particle time:
Result:
We can understand the particle nature inside the cyclone seperator were we understand particles that got trapped and numer of them which escaped
Mesh element size 15 mm 10mm 12mm
Number tracked 132 364 220
escaped 132 330 208
aborted 0 0 0
trapped 0 0 0
evaporated 0 0 0
incomplete 0 34 12
Conclusion:
- The discrete phase boundry condition did not have a major impact on result as the results obtained were almost same.
- Mesh size has a prominent effect on scaled residuals as well as the tracing of particles
- We see most of the particles escaped from the bottom which is because of the gravity