Discrete phase modelling of air flow through a cyclone separator in Ansys Fluent
Objective
- Writing a few words about the four empirical models used for cyclone separator efficiency
- Performing 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
- Varying 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
Cyclone separator
Schematic diagram of cyclone separator
Working Principle
A cyclone is a centrifugal separator in which particles, due to their mass, are pushed to the outer edges as a result of centrifugal force. Incoming air is automatically forced to adopt a fast-revolving spiral movement - the so-called double vortex. This double spiral movement consists of an outer stream, which flows downwards in a spiral, and an inner stream, which flows upwards in a spiral. At the interchange between both streams, air passes from one stream to the other. The particles which are present in the air are forced to the outer edges and leave the separator via a collection device fitted to the bottom of the separator.
Materials
In the presence of substances and liquids with a strong corrosive or erosive nature, cyclones must be made of a suitable material or be coated with an appropriate substance. Cyclones are available in various materials such as stainless steel, aluminium, nickel, polystyrene (PS), polyvinylchloride (PVC) and polyvinylidenefluoride (PVDF).
Application
- Wood and furniture industry
- The building sector
- Glass industry
- The transport sector for storage and transfer
- The foodstuffs industry
- Waste combustion installations
- The chemicals industry.
Empirical models used for cyclone separator efficiency
1.Iozia and Leith Model
Iozia and Leith logistic model is a modified version of Barth 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. The collection efficiency ηi of particle diameter dpi can be calculated from
β- is an expression for slope parameter derived based on the statistical analysis of experimental data of a cyclone with D =0.25 m given as
2.Li and Wang Model
The Li and Wang 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 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 turbulent diffusion coefficient and particle bounce reentrainment on the cyclone wall are:-
C=C0,at`theta=0`
`Drfrac{delC}{delr}`=(1-α)wc, at r=D/2
- The tangential velocity is related to the radius of cyclone by `uR^n` = constant.
- The resultant expression of the collection efficiency for particle
of any size is given as
ηi = 1 − exp{−λθ1}
where,
θ1 = 2`pi`(S + L)/a
3.Koch and Licht Model
Koch and Licht 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 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 `uR^n` = 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 `tau` is the relaxation term
4.Lapple Model
Lapple 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 semiempirical relationship developed by Lapple to calculate a
50% cut diameter, dpc, is
where Ne is the number of revolutions
Ne=`frac{1}{a}[h+frac{H-h}{2}]`
The efficiency of collection of any size of particle is given by
Part 1
Case 1:Discrete Phase Boundary Condition Type-Escape
Step 1:Geometry
- In order to do discrete phase simulation on cyclone separator we need to extract fluid volume which we can see in the below image
Step 2:Meshing
- Before proceeding with meshing first we need to assign name selection which we can see in the below image
- Element Size=25mm
- Total Number of elements generated=157237
- Total Number of nodes generated=31387
Step 3.Setup
- Solver:Steady-state
- Type:Pressure based
- Viscous model: K-epsilon with RNG ,since the flow is turbulent
- Fulid flow:Air
- Gravity Enabled:X & Z=0 m/s^2:Y=-9.81m/s^2
Discrete Phase Model
- Interaction with continuous phase,since we are assunimg coupled flow
- Update DPM sources every flow iteration
- Injection name:Injection_0
- Injection type:Surface
- Material:Anthracite
- Point properties:X_velocity=3m/s
- Diameter=5e-6
Boundary condition:
- Inlet velocity=3m/s
- DPM boundary type=Escape
- Now,we will initialize the solution using Standard scheme.
- Numbe of iteration=300
Plots
Residue
- From above image its quite clear that solution get converge around 270th iteration
Console output
Anthracite Particle Time
Animation of Anthracite Particle Time
Case 2:Discrete Phase Boundary Condition Type-Reflect
Step 1:Geometry
- In order to do discrete phase simulation on cyclone separator we need to extract fluid volume which we can see in the below image
Step 2:Meshing
- Before proceeding with meshing first we need to assign name selection which we can see in the below image
- Element Size=25mm
- Total Number of elements generated=157237
- Total Number of nodes generated=31387
Step 3.Setup
- Solver:Steady-state
- Type:Pressure based
- Viscous model: K-epsilon with RNG ,since the flow is turbulent
- Fulid flow:Air
- Gravity Enabled:X & Z=0 m/s^2:Y=-9.81m/s^2
Discrete Phase Model
- Interaction with continuous phase,since we are assunimg coupled flow
- Update DPM sources every flow iteration
- Injection name:Injection_0
- Injection type:Surface
- Material:Anthracite
- Point properties:X_velocity=3m/s
- Diameter=5e-6
Boundary condition:
- Inlet velocity=3m/s
- DPM boundary type=Reflect
- Now,we will initialize the solution using Standard scheme.
- Numbe of iteration=300
Plots
Residue
- From above image its quite clear that solution get converge around 215th iteration
Console Output
Anthracite Particle Time
Vortex region
Animation of Anthracite Particle Time
Case 3:Discrete Phase Boundary Condition Type-Trap
Step 1:Geometry
- In order to do discrete phase simulation on cyclone separator we need to extract fluid volume which we can see in the below image
Step 2:Meshing
- Before proceeding with meshing first we need to assign name selection which we can see in the below image
- Element Size=25mm
- Total Number of elements generated=157237
- Total Number of nodes generated=31387
Step 3.Setup
- Solver:Steady-state
- Type:Pressure based
- Viscous model: K-epsilon with RNG ,since the flow is turbulent
- Fulid flow:Air
- Gravity Enabled:X & Z=0 m/s^2:Y=-9.81m/s^2
Discrete Phase Model
- Interaction with continuous phase,since we are assunimg coupled flow
- Update DPM sources every flow iteration
- Injection name:Injection_0
- Injection type:Surface
- Material:Anthracite
- Point properties:X_velocity=3m/s
- Diameter=5e-6
Boundary condition:
- Inlet velocity=3m/s
- DPM boundary type=Trap
- Now,we will initialize the solution using Standard scheme.
- Numbe of iteration=300
Plots
Residue
- From above image its quite clear that solution get converge around 215th iteration
Console Output
Anthracite Particle Time
Vortex region
Animation of Anthracite Particle Time
Case 4:Discrete Phase Boundary Condition Type-Wall-Jet
Step 1:Geometry
- In order to do discrete phase simulation on cyclone separator we need to extract fluid volume which we can see in the below image
Step 2:Meshing
- Before proceeding with meshing first we need to assign name selection which we can see in the below image
- Element Size=25mm
- Total Number of elements generated=157237
- Total Number of nodes generated=31387
Step 3.Setup
- Solver:Steady-state
- Type:Pressure based
- Viscous model: K-epsilon with RNG ,since the flow is turbulent
- Fulid flow:Air
- Gravity Enabled:X & Z=0 m/s^2:Y=-9.81m/s^2
Discrete Phase Model
- Interaction with continuous phase,since we are assunimg coupled flow
- Update DPM sources every flow iteration
- Injection name:Injection_0
- Injection type:Surface
- Material:Anthracite
- Point properties:X_velocity=3m/s
- Diameter=5e-6
Boundary condition:
- Inlet velocity=3m/s
- DPM boundary type=Wall-Jet
- Now,we will initialize the solution using Standard scheme.
- Numbe of iteration=300
Plots
Residue
- From above image its quite clear that solution get converge around 215th iteration
Console Output
Anthracite Particle Time
Vortex Region
Animation of Anthracite Particle Time
Part 2
Case 1:Discrete Phase Boundary Condition Type-Reflect
Step 1:Geometry
- In order to do discrete phase simulation on cyclone separator we need to extract fluid volume which we can see in the below image
Step 2:Meshing
- Before proceeding with meshing first we need to assign name selection which we can see in the below image
- Element Size=25mm
- Total Number of elements generated=157237
- Total Number of nodes generated=31387
Step 3.Setup
- Solver:Steady-state
- Type:Pressure based
- Viscous model: K-epsilon with RNG ,since the flow is turbulent
- Fulid flow:Air
- Gravity Enabled:X & Z=0 m/s^2:Y=-9.81m/s^2
Discrete Phase Model
- Interaction with continuous phase,since we are assunimg coupled flow
- Update DPM sources every flow iteration
- Injection name:Injection_0
- Injection type:Surface
- Material:Anthracite
- Point properties:X_velocity=3m/s
- Diameter=5e-6
Boundary condition:
- Inlet velocity=3m/s
- DPM boundary type=Escape
- Now,we will initialize the solution using Standard scheme.
- Numbe of iteration=300
Plots
Residue
- From above image its quite clear that solution get converge around 215th iteration
Console Output
Anthracite Particle Time
Vortex region
Animation of Anthracite Particle Time
Case 2:Discrete Phase Boundary Condition Type-Reflect
Step 1:Geometry
- In order to do discrete phase simulation on cyclone separator we need to extract fluid volume which we can see in the below image
Step 2:Meshing
- Before proceeding with meshing first we need to assign name selection which we can see in the below image
- Element Size=20mm
- Total Number of elements generated=76723
- Total Number of nodes generated=15748
Step 3.Setup
- Solver:Steady-state
- Type:Pressure based
- Viscous model: K-epsilon with RNG ,since the flow is turbulent
- Fulid flow:Air
- Gravity Enabled:X & Z=0 m/s^2:Y=-9.81m/s^2
Discrete Phase Model
- Interaction with continuous phase,since we are assunimg coupled flow
- Update DPM sources every flow iteration
- Injection name:Injection_0
- Injection type:Surface
- Material:Anthracite
- Point properties:X_velocity=3m/s
- Diameter=5e-6
Boundary condition:
- Inlet velocity=3m/s
- DPM boundary type=Escape
- Now,we will initialize the solution using Standard scheme.
- Numbe of iteration=300
Plots
Residue
- From above image its quite clear that solution get converge around 215th iteration
Console Output
Anthracite Particle Time
Vortex region
Animation of Anthracite Particle Time
Case 3:Discrete Phase Boundary Condition Type-Reflect
Step 1:Geometry
- In order to do discrete phase simulation on cyclone separator we need to extract fluid volume which we can see in the below image
Step 2:Meshing
- Before proceeding with meshing first we need to assign name selection which we can see in the below image
- Element Size=10mm
- Total Number of elements generated=407130
- Total Number of nodes generated=79480
Step 3.Setup
- Solver:Steady-state
- Type:Pressure based
- Viscous model: K-epsilon with RNG ,since the flow is turbulent
- Fulid flow:Air
- Gravity Enabled:X & Z=0 m/s^2:Y=-9.81m/s^2
Discrete Phase Model
- Interaction with continuous phase,since we are assunimg coupled flow
- Update DPM sources every flow iteration
- Injection name:Injection_0
- Injection type:Surface
- Material:Anthracite
- Point properties:X_velocity=3m/s
- Diameter=5e-6
Boundary condition:
- Inlet velocity=3m/s
- DPM boundary type=Escape
- Now,we will initialize the solution using Standard scheme.
- Numbe of iteration=300
Plots
Residue
- From above image its quite clear that solution get converge around 215th iteration
Console Output
Anthracite Particle Time
Vortex region
Animation of Anthracite Particle Time
Conclusion
- The flow of particles through cyclone separator is successfully simulated
- The particles has been tracked for different discrete phase boundary condition
- Refining the mesh leads to increase in injected particles
- Mesh refinement leads to better tracking of the particles
Comparsion of Results for different discrete phase boundary condition
Comparsion of Results of different Mesh Size for Reflect Discrete phase boundary condition
References: