Week 8 - Simulating Cyclone separator with Discrete Phase Modelling

Aim:- To perform analysis on cyclone separator and calculate the separation efficiency and pressure drop.

Objective:-

1. To write a few words about any four empirical models used to calculate the cyclone separator efficiency.
2. To perform an analysis on a given cyclone separator model by varying the particle diameter from 1 μm to 5 μm and calculate the separation efficiency in each case. Discuss the results. [Use both the velocity's as 3m/sec.]
3. To perform an analysis on a given cyclone separator model by varying the particle velocity from 1 m/sec to 5 m/sec and calculate the separation efficiency and pressure drop in each case. Discuss the results. [Use particle diameter size as 5 μm for all cases & keep flow velocity same as particle velocity]

CYCLONE EFFICIENCY EMPIRICAL MODELS

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 η_i of particle diameter d_pi can be calculated from,

2. Li and Wang Model

The Li and Wang [3] 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
• Boundary conditions with the consideration of turbulent diffusion coefficient and particle bounce re-entrainment on the cyclone wall are.

3. Koch and Licht Model

Koch and Licht collection theory recognized the in herently 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 tan- gential velocity of the gas flow, 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.

4. Lapple Model

Lapple model was developed based on force balance with- out 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 [1] to calculate a 50% cut diameter, d_pc, is,

GEOMENTRY:

MESHING:

NAME SELECTION: Select all the inlet and outlet faces and name them accordingly.

The cylone seperator has been meshed with an element size of 15mm.

The cartesian method is used to make the mesh structural.

SETUP METHOD: viscous model is k-epsilon with standard wall function.

Discrete phase is used to define the injecting particles size and velocity.

BOUNDARY CONDITION:

INLET: REFLECT
OUTLET_1: TRAP(BOTTOM)
OUTLET_2: ESCAPE (TOP)

METHOD (COUPLED) AND THE HYBRID INISILIZATION:

PLOTS FOR VEL 3m/s AND DIA 1μm:

CONTOUR:

SCALE RESIDUALS:

SWRIL MOMENTUM:

PLOTS FOR VEL 3m/s AND DIA 3μm:

CONTOUR:

SCALE RESIDUALS:

SWRIL MOMENTUM:

PLOTS FOR VEL 3m/s AND DIA 5μm:

CONTOUR:

SCALE RESIDUALS:

SWRIL MOMENTUM:

PLOTS FOR VEL 1m/s AND DIA 5μm:

CONTOUR:

SCALE RESIDUALS:

SWRIL MOMENTUM:

PLOTS FOR VEL 5m/s AND DIA 5μm:

CONTOUR:

SCALE RESIDUALS:

SWRIL MOMENTUM:

RESULTS:

CASE	TRACKED	ESCAPED	TRAPPED	INCOMPLETE	EFFICIENCY
1	91	28	63	-	32.49
2	91	35	47	9	10.53
3	91	36	52	3	15.61
4	91	37	12	42	1.125
5	91	25	66	-	35.17

• Number of particles trapped depends on the size of the element, So smaller the size greater the escape.
• Same particles and the inlet velocity flow, there is an increases in the particle size diameter and efficiency decreases.This suituation is obsereved in the case 1.
• same particle diameter and increase in the velocity flow, there is a decrease in the seperator efficiency. which is observered in case 2.

REFERENCE:

https://www.researchgate.net/publication/232747389_A_CFD_Study_on_the_Prediction_of_Cyclone_Collection_Efficiency