Cyclone Separator Challenge
Cyclone seperator challenge
Objective:
- Perform an analysis on the given cyclone separator model using four different boundary condition types at the inlet i.e. reflect, trap, escape and wall-jet.
- Vary the number of particles through the inlet and run the simulation for 3 cases using the “Reflect” option as the boundary condition for the Discrete Phase
Cyclone seperator:
- cyclone seperature is a conical device
- it works on the means of separating different solid, liquid and gases phases (different densities). Heavier particals move to the bottom of the chamber and
1.Empirical models used for cyclone separator efficiency:
I. IOZIA AND LEITH MODEL:
Iozia and Leith (1990) logistic model is a modified version of Barth (1956) model which is developed based on forcebalance. 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,z , and core diameter, d.The collection efficiency ηi of particle diameter d. pi can be calculated from
II. 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
The resultant expression of the collection efficiency for particle of any size is given as
III. 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 Lichtdescribe particle motion in the entry and collection regionswith the additional following assumptions:
- The tangential velocity of a particle is equal to the tangentialvelocity of the gas flow, i.e. there is no slip in the tangentialdirection between the particle and the gas.
- The tangential velocity is related to the radius of cyclone by:
uR = constant.
A force balance and an equation on the particles collectionyields the grade efficiency ηi.
IV. LAPPLE MODEL:
Lapple (1951) model was developed based on force balance without considering the flow resistance. Lapple assumed that aparticle entering the cyclone is evenly distributed across theinlet opening. The particle that travels from inlet half width tothe wall in the cyclone is collected with 50% efficiency.Thesemi empirical relationship developed by Lapple (1951) tocalculate a 50% cut diameter,d., is
The efficiency of collection of any size of particle is given by
Geometry:
Cyclone seperator consists of one inlet and two outlets. Inlet is at the side of the seperator and outlets are at the bottom and top. this is the given geometry from which fluid volume to be extracted
stand is removed since it is not involved in the simulation process. Actual seperator can be seen now.
Using the volume extraction and fluid volume is extracted. All the cases run using this extracted volume.
2.Analysis on the given cyclone separator model using four different boundary condition types at the inlet:
Meshing: Base mesh size is 10mm and there are about 364 cells at the inlet which means same number of particals will be simulated. Mesh is same for next four simulation results.
It is a fine mesh because of the number of cells that are present in the volume.
Case setup:
Solver: steady state, pressure based and absolute.
Gravity: -9.81 m/s in z direction.
Models: Viscous model - K-ephsilon, RNG, Swirl dominated flow, standard wall function.
Discrete phase model-Interaction
Screenshot explains the setting of the DPM. Once the everthing is checked, injections should be modeled.
Injection of the antracite particals which are at inform diameter are done at the inlet. Diameter of the particle is 5e-6 and total flow rate is 1e-20. Pumped into the inlet at a velocity of 3m/s.
boundary conditons: inlet is set as velocity inlet and magnitude is set to 5 m/s.
Intialization: standard initialization calculated from inlet.
Simulation runs for 600 iterations
Solution and results:
Case-1: In this case, particle behaviour is described in Discrete phase BC type as \'Reflect\'.
simulation residuals plot are smooth and has little fluctions at the begining.
This is the main data which reveals how many particles are tracked, escaped and incomplete. Escaped particles either escaped bottom outlet or top outlet. Incomplete
Contour of the particles that are in the vortex region inside the cyclone seperator. 100 particles are displayed out of 364.
contour of vortex that is created due to the particle velocity and the design of the cyclone seperator.
Case-2: In this case, particle behaviour is described in Discrete phase BC type as \'Trap\'.
simulation residuals plot are smooth and has little fluctions at the begining. There is no change in the residuals performance compared to above case.
No change in the results compared to case1.
Contour of the particles that are in the vortex region inside the cyclone seperator. 100 particles are displayed out of 364.
contour of vortex that is created due to the particle velocity and the design of the cyclone seperator.
Case-3: In this case, particle behaviour is described in Discrete phase BC type as \'escape\'.
simulation residuals plot are smooth and has little fluctions at the begining. There is no change in the residuals performance compared to above cases.
No change in the results compared to above cases.
Contour of the particles that are in the vortex region inside the cyclone seperator. 100 particles are displayed out of 364.
contour of vortex that is created due to the particle velocity and the design of the cyclone seperator.
Case-3: In this case, particle behaviour is described in Discrete phase BC type as \'wall-jet\'.
simulation residuals plot are smooth and has little fluctions at the begining. There is no change in the residuals performance compared to above cases.
No change in the results compared to above cases.
Contour of the particles that are in the vortex region inside the cyclone seperator. 100 particles are displayed out of 364.
contour of vortex that is created due to the particle velocity and the design of the cyclone seperator.
3. Varying the number of particles through the inlet and run the simulation for 3 cases using the “Reflect” option as the boundary condition for the Discrete Phase:
Case-5: No of particles that enter in to the inlet depends on the number of cells that are present at the face of the inlet. In this case we have 364 cells. This no of cells is achieved by base mesh size of 10mm.
It is a fine mesh because of the number of cells that are present in the volume.
simulation residuals plot are smooth and has little fluctions at the begining. There is no change in the residuals performance compared to above cases.
No change in the results compared to above cases.
Contour of the particles that are in the vortex region inside the cyclone seperator. 100 particles are displayed out of 364.
contour of vortex that is created due to the particle velocity and the design of the cyclone seperator.
Case-6: No of particles that enter in to the inlet depends on the number of cells that are present at the face of the inlet. In this case we have 132 cells. This no of cells is achieved by base mesh size of 15mm.
This is a coarse mesh compared to the above case.
simulation residuals plot are smooth and has little fluctions at the begining and middle.
even thought the mesh is coarse there are no trapped or aborted particles observed in the domain.
Contour of the particles that are in the vortex region inside the cyclone seperator 100 particles are displayed out of 134.
contour of vortex that is created due to the particle velocity and the design of the cyclone seperator.
Case-7: No of particles that enter in to the inlet depends on the number of cells that are present at the face of the inlet. In this case we have 94 cells. This no of cells is achieved by base mesh size of 20mm.
This is a very coarse mesh compared to the above case.
simulation residuals plot shows high fluctions. Fluctuations are the result if very coarse mesh used.
Because of the coarse mesh we can see that there are very high number of incomplete particle.
Contour of the particles that are in the vortex region inside the cyclone seperator. 94 particles are displayed out of 94.
contour of vortex that is created due to the particle velocity and the design of the cyclone seperator.
CONCLUSION:
- Discrete phase Boundary condition type has a negligible effect on the tracing of a particle. for the trap and escape condition we can see that two particles are escaping from top outlet where for the other two only one is exiting from top.
- Mesh size has a prominent effect on the residuals as well as the tracig of the particles.
- Due to poor mesh or coarse mesh many particles in the vortex were untraced and declared as incomplete.
- A miniute number of particles escaped from the top outlet.
- Gravity has huge impact on the particle. since most of the particles escaped from bottom outlet.