Cyclone Separator Simulation using different DPM types
Cyclone Separator Simulation using different DPM types.
Introduction -
Cyclone Separators -
Cyclone separators or simply cyclones are separation devices that use the principle of inertia to remove particulate matter from flue gases. Cyclone separators is one of many air pollution control devices known as precleaners since they generally remove larger pieces of particulate matter. They use the centrifugal force generated by a spinning stream to separate particles from each other. Their simple design,low maintainence cost and great adaptability has made them one of the of most used particle separator. There are four different cyclone separator efficiency empricial models based on the efficiency they give. they are listed below :
1) Cyclone separator efficiency empiricial models -
Cyclone Separators -
Cyclone separators or simply cyclones are separation devices that use the principle of inertia to remove particulate matter from flue gases. Cyclone separators is one of many air pollution control devices known as precleaners since they generally remove larger pieces of particulate matter. They use the centrifugal force generated by a spinning stream to separate particles from each other. Their simple design,low maintainence cost and great adaptability has made them one of the of most used particle separator. There are four different cyclone separator efficiency empricial models based on the efficiency they give. they are listed below :
a) 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
The addition made by Iozia and Leith on the original Barth (1956) model are the core length zc and slope parameter β expression which is derived based on the statistical analysis of experimental data of cyclone with D = 0.25 m. The collection efficiency ηi of particle diameter dpi can be calculated from
b) LI AND WANG MODEL
The Li and Wang (1989) model includes particle bounce or re-entrainment and turbulent diffusion at the cyclone wall. A two-dimensional analytical expression of particle distribution in the cyclone is obtained. Li and Wang model was developed based 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 are:
c = c0, at θ = 0
Dr ∂c/∂r = (1- α)wc, at r = D/2
The tangential velocity is related to the radius of cyclone by: uRn = constant.
The concentration distribution in a cyclone is given as:
c) KOCH AND LICHT MODEL
Koch and Licht (1977) collection theory recognized the inherently turbulent nature of cyclones and the distribution of gas residence times within the cyclone. Koch and Licht describe particle motion in the entry and collection regions with 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.
A force balance and an equation on the particles collection
yields the grade efficiency ηi.
G is a factor related to the configuration of the cyclone, n is related to the vortex and τ is the relaxation term.
d) 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 semi empirical relationship developed by Lapple (1951) to calculate a 50% cut diameter, dpc, is
2) Analysis of cyclone separator -
Geometry -
Mesh -
Element size - 10 mm
No. of elements - 411074
No. of nodes - 80162
Mesh quality -
Fluent preparations -
Setup -
Type - pressure based, Absolute,steady state
Model - K-epsilon - RNG - Swirl dominated flow
Discrete phase model - interaction with continuous phase - update DPM sources for every 10 iterations - max. number of steps(50000) for step length factor as 5
Injections - create - injection type(surface) - select inlet - particle type(inert) - material(anthracite) - Diameter distribution(uniform) - point properties (X-velocity as 3 m/s) - Particle diameter(5e-06) - total flow rate(1e-20) - Ok
Boundary conditions - inlet - momentum - velocity magnitude as 3 m/s
Boundary conditions - inlet - DPM - reflect/trap/escape/wall-jet
Solution -
methods - turbulent kinetic energy(second order upwind) - turbulent dissipation rate(second order upwind)
Monitors - initialization - Standard initialization -compute from inlet - initialize
Run calcualtion - run it for 600 iterations
Results -
a) DPM type - Reflect
No of particles tracked - 364
No of particles escaped - 139
No of particles aborted - 0
No. of particles trapped - 0
No of particles evaporated - 0
No of particles incomplete - 225
i) residual plot -
ii) Particle time plot -
iii) vortex -
iv) Animation -
b) DPM type - Trap
No of particles tracked - 364
No of particles escaped - 139
No of particles aborted - 0
No. of particles trapped - 0
No of particles evaporated - 0
No of particles incomplete - 225
i) Residual plot -
ii) particle time plot -
iii) vortex -
iv) Animation -
c) DPM type - Escape
No of particles tracked - 364
No of particles escaped - 139
No of particles aborted - 0
No. of particles trapped - 0
No of particles evaporated - 0
No of particles incomplete - 225
i) Residual plot -
ii) particle time plot -
iii) Vortex -
iv) Animation -
d) DPM type - Wall-jet
No of particles tracked - 364
No of particles escaped - 139
No of particles aborted - 0
No. of particles trapped - 0
No of particles evaporated - 0
No of particles incomplete - 225
i) Residual plot -
ii) Particle time plot -
iii) Vortex -
iv) Animation -
3) Different cases for DPM type - Reflect
Case I -
Mesh -
Element size - 10 mm
No. of elements - 411074
No. of nodes - 80162
Mesh quality -
Residual plot -
Particle time plot -
No of particles tracked - 364
No of particles escaped - 139
No of particles aborted - 0
No. of particles trapped - 0
No of particles evaporated - 0
No of particles incomplete - 225
Vortex for 10 mm -
Animation for 10 mm -
Case II -
Mesh -
Element size - 25 mm
No of elements - 44838
No. of Nodes - 9386
Mesh quality -
Residual plot -
Particle time plot -
No of particles tracked - 52
No of particles escaped - 45
No of particles aborted - 0
No. of particles trapped - 0
No of particles evaporated - 0
No of particles incomplete - 7
Vortex -
Animation -
Case III -
Mesh -
Element size - 50 mm
No of elements - 18639
No of nodes - 4077
Mesh quality -
Residual plot -
Particle time plot -
No of particles tracked - 14
No of particles escaped - 14
No of particles aborted - 0
No. of particles trapped - 0
No of particles evaporated - 0
No of particles incomplete -0
Vortex -
Animation -
Conclusion -
1) As the mesh gets finer, more particles flow through the inlet
2) The number of particles tracked,escaped for different DPM types are same.
3) As the mesh gets finer, the number of particles tracked,escaped for same DPM type are different.