Week 8 - Simulating Cyclone separator with Discrete Phase Modelling

Cyclone-Separator Challenge

4 Emperical methods used to calculate the Cyclone-Separator Efficiency

Research Paper used: http://dspace.unimap.edu.my/xmlui/bitstream/handle/123456789/13571/054-058_empirical%20models.pdf?sequence=1

1. Iozia and Leith Model

It is model based on modification of barth model. It assumes that particle is carried out by 2 forces, centrifugal force and resistance.

Dpi = particle size

2. Li and Wang Model

This includes particle bounce , re-entrainment, turbulent diffusion at the wall.

3. Koch and licht Model

They recognised the inherently turbulent nature of cyclones and distribution of gas residence times within the cyclone. The tangential velocity is related to radius of cyclone as uRn=constant.

4. Lapple Model

It is based on force balance without considering flow resistance. The particle that leaves from inlet half width to wall is collected with 50 percent efficiency. Calculating a 50 % cut diameter dpc as:

Geometry

Load geometry, extract fluid volume, remove outerline edges on inlet and outlet, suppress solid volume for physics.

Mesh

Element size-5mm

Mesh> Insert Method> cartesian method for a structured mesh

Always clear generated data first if you change mesh settings.

Set-Up:

Steady state simulation, pressure based solver, gravity enabled field in y direction =-9.81 m/s2

Model- RNG K-epsilon, swirl dominated flow

Setup the discrete phase modelling:

Injection- material type- anthracite at inlet, type-surface, input velocity in x direction as direction is the one normal to our chosen surface(here inlet). Input the particle size as per case also.

Boundary conditions –

Inlet- input velocity, DPM- reflect

Outlet-1(top)= DPM-escape

Outlet-2(bottom)= DPM-trap

Wall-reflect

Solution –

Scheme- Coupled

Second order upwind scheme used.

Initialize>standard>options

Compute from-inlet > check velocities for x,y,z direction

Uncheck for convergence.

Run calculation for 600 iterations and create report definition for pressure at inlet and bottom outlet.

Export the particle history data and import it while you are in cfd post.

Post-Processing

Case1: Particle size= 1e-6 and velocity=3m/s

Residual:

Particle Tracked	378
Particle Trapped	146
Particle escaped	162
incomplete	70
Efficiency	38.62%
Pressure inlet	28.122
Pressure outlet	-0.011
Pressure Drop	28.133

Anthracite particle time:

Case2: Particle size= 3e-6 and velocity=3m/s

Particle Tracked	378
Particle Trapped	150
Particle escaped	87
incomplete	141
Efficiency	39.6%
Pressure inlet	28.122
Pressure outlet	-0.011
Pressure Drop	28.133

Case3: Particle size= 5e-6 and velocity=3m/s

Particle Tracked	378
Particle Trapped	291
Particle escaped	62
incomplete	25
Efficiency	76.9%
Pressure inlet	27.42
Pressure outlet	-0.01
Pressure Drop	27.43

Case4: Particle size= 5e-6 and velocity=1m/s

Particle Tracked	378
Particle Trapped	10
Particle escaped	106
incomplete	262
Efficiency	2.6%
Pressure inlet	2.45
Pressure outlet	-0.0001
Pressure Drop	2.45

Case5: Particle size= 5e-6 and velocity=5m/s

Particle Tracked	378
Particle Trapped	232
Particle escaped	66
incomplete	80
Efficiency	61.3%
Pressure inlet	82.2
Pressure outlet	-0.03
Pressure Drop	82.2

Conclusion:

Particle size(v=3)	Efficiency
1e-6	38.6%
3e-6	39.6%
5e-6	76.9%

As particle size increases , the separator efficiency for cyclone separator increases drastically. With a particle size of 5 micron, efficiency is 76.9 which is very high. This is the case when velocity is same i.e 3 m/s for all cases. Pressure drop in all the 3 cases remain same.

Particle velocity(size=5e-6)	Efficiency
1m/s	2.6%
3m/s	76.9%
5m/s	61.3%

We can see that when particle size is kept same and the velocity is varied, the efficiency drastically increases even with a little increase velocity.