Week 8 - Simulating Cyclone separator with Discrete Phase Modelling
AIM: to simulate the flow through a cyclone separator and showing the results for the different particle size and for the different velocities.
we have to run the simulation for the six cases
1).set the velocity constant to 3 m/s and do simulation for the varying size of the particle.
2).set the particle size to constant and simulate for the different velocities.
Models of the cyclone separator:
Cyclone Separator :
Cyclone separators or simply cyclones are separation devices (dry scubbers) that use the principle of inertia to remove particulate matter from flue gases . Cyclone separators is one of many air pollution removers 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. In addition, several cyclone separators can operate in parallel, and this system is known as a multicyclone
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. This spiral formation and the separation is shown in Figure . 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. Contrarily, larger components of particulate matter have more inertia and are not as easily influenced by the vortex.
Since these larger particles have difficulty following the high-speed spiral motion of the gas and the vortex, the particles hit the inside walls of the container and drop down into a collection hopper. These chambers are shaped like an upside-down cone to promote the collection of these particles at the bottom of the container. The cleaned flue gas escapes out the top of the chamber.
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 are given as:
β is an expression for slope parameter derived based on the
statistical analysis of experimental data of a cyclone with D = 170
0.25 m given as:
and dpc is the 50% cut size given by Barth:
where core length, zc, and core diameter, dc, are given as
Li and Wang Model :
The Li and Wang [3] model includes particle bounce or reentrainment and turbulent diffusion at the cyclone wall. A twodimensional analytical expression of particle distribution in the
cyclone is obtained. Li and Wang model was developed based
180 on the following assumptions:
The radial particle velocity and the radial concentration
profile are not constant for uncollected particles within
the cyclone.
Boundary conditions with the consideration of turbu185 lent diffusion coefficient and particle bounce reentrainment on the cyclone wall are:
Koch and Licht Model:
Koch and Licht [2] collection theory recognized the inherently turbulent nature of cyclones and the distribution of gas
residence times within the cyclone. Koch and Licht described
particle motion in the entry and collection regions with the ad- 200
ditional 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 cy- 205
clone by: u Rn = constant.
A force balance and an equation on the particles collection yields
the grade efficiency ηi:
Lapple Model:
Lapple [1] model was developed based on force balance without considering the flow resistance. Lapple assumed that a par215 ticle 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 semi
empirical relationship developed by Lapple [1] to calculate a
50% cut diameter, dpc, is:
Modeling approach:
Geometry:Fluid Volume extracted using SpaceClaim is shown below:
Min Element Size: 10mm
The faces are selected and names as inlet , outlet_1, outlet_2. As the orientation is in XY plane so the gravity is given in -Y direction.
K-epsilon solver is used which is decided by Y+ value. The swirl dominated RNG model is used here to capture the flow more accurately.
The Discrete phase modeling is used to track the flow of the particles.
No of step for particle tracking = 50000
Injection Material : Anthracite (5microns in diameter)
Velocity Inlet: 3m/s
Outlet: Pressure Outlet
Reflect: The particle rebounds off the boundary with momentum change due to coeff of restitution.
Escape: Particles escape out when encountered at boundary
Trap: The trajectory calculation is terminated and the particle is traped.
Results:
Results for the particle size of 1 micron with a velocity of 3m/s
residuals graph:
No. of particle tracked = 98
No. of particle trapped = 52
No. of particle escaped = 38
No. of particle incomplete = 8
Separation Efficiency in % = (52 / 98) * 100
Separation Efficiency = 53.06 %
Results for the particle size of 2 micron with a velocity of 3m/s .
residuals graph:
No. of particle tracked = 98
No. of particle trapped = 75
No. of particle escaped = 23
Separation Efficiency in % = (75 / 98) * 100
Separation Efficiency = 76.53 %
Results for the particle size of 5 micron with a velocity of 3m/s .
residuals graph:
No. of particle tracked = 98
No. of particle trapped = 98
No. of particle escaped = 0
Separation Efficiency in % = (98 / 98) * 100
Separation Efficiency = 100 %
Case 2: Inlet velocity of the particle and the discrete phase is same i.e 1m/s
residuals graph:
Total Pressure:
Pressure drop = Total inlet pressure - Total Outlet Pressure
= 3.15 – 0.36
Pressure drop =2.79 Pa
No. of particle tracked = 98
No. of particle trapped = 7
No. of particle escaped = 24
No. of particle icomplete = 67
Separation Efficiency in % = (7 / 98) * 100
Separation Efficiency = 7.14 %
inlet velocity of the particle and the discrete phase is same i.e 3m/s
residuals graph:
Total Pressure:
Pressure drop = Total inlet pressure - Total Outlet Pressure
= 33.93 – 4.09
Pressure drop =29.83 Pa
No. of particle tracked = 98
No. of particle trapped =98
No. of particle escaped = 0
No. of particle icomplete = 0
Separation Efficiency in % = (98 / 98) * 100
Separation Efficiency = 100 %
inlet velocity of the particle and the discrete phase is same i.e 5m/s
residuals graph:
Total Pressure:
Pressure drop = Total inlet pressure - Total Outlet Pressure
= 98.93 – 12.04
Pressure drop =86.89 Pa
No. of particle tracked = 98
No. of particle trapped =98
No. of particle escaped = 0
No. of particle icomplete = 0
Separation Efficiency in % = (98 / 98) * 100
Separation Efficiency = 100 %