Week 8 - Simulating Cyclone separator with Discrete Phase Modelling

Objective:

To simulate cyclone separator with Discrete Phase Modelling in Ansys fluent.

Theory:

Empirical models used to calculate the 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.

2.Li and Wang Model

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 re-entrainment on the cyclone wall

3.Koch and Licht Model

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 the cyclone by: u Rn = constant.

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.

from the research paper https://www.researchgate.net/publication/232747389_A_CFD_Study_on_the_Prediction_of_Cyclone_Collection_Efficiency

The Li and Wang model and CFD code both predict very well the cyclone efficiency and cut-off size for any operational conditions. In all operating conditions and cyclone types, the FLUENT CFD and Li and Wang model were found to be much closer to the experimental measurement. However, only the FLUENT CFD code consistently predicts the cyclone cut-off size. Therefore, both the Li and Wang model and FLUENT CFD code can be used to evaluate the collection efficiency in the cyclone design except for the extreme operating temperatures, which is Li and Wang model is less accurate

Meshing:

structured mesh using the cartesian method.

Residuals:

Flow rate at outlet_2

velocity at the outlet_1

Particle track Video:

https://youtu.be/ypeN1jk6Kh0

Particle size	Number tracked	Escaped	Trapped	Incomplete	Efficiency
1 micrometer	153	52	90	11	58.8%
2 micrometer	153	47	101	5	66.01%
3 micrometer	153	39	113	1	73.85%
4 micrometer	153	38	115	0	75.16%
5 micrometer	153	36	116	1	75.81%

Velocity ( m/s )	Number tracked	Escaped	Trapped	Incomplete	Pressure drop (pascal)	Efficiency %
1	153	39	10	104	1.89	6.53%
2	153	38	113	2	8.35	73.85%
3	153	36	116	1	19.42	75.82%
4	153	36	117	0	35.22	76.47%
5	153	34	119	0	55.82	77.77%

Conclusion:

• Thus the simulation is done using the Ansys fluent.
• Efficiency drops with low velocity and smaller particle size.