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 theseparation 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 separator:

1.Cyclone separators or simply cyclones are separation devices that use the principle of inertia to remove particulate matterfrom flue gases

2.Cyclone separators is one of many air pollution controlling devices known as precleaners since they generally remove larger pieces of particulate matter.

3.This prevents finer filtration methods from having to deal with large, more abrasive particles later on. In addition, several cyclone separators can operate in parallel, and this system is known as a multicyclone.

4.It is important to note that cyclones can vary drastically in their size. The size of the cyclone depends largely on how much flue gas must be filtered, thus larger operations tend to need larger cyclones.

Working:

1.Cyclone separators work much like a centrifuge, but with a continuous feed of dirty air.

2.In a cyclone separator, dirty flue gas is fed into a chamber.which creates a spiral vortex, similar to a tornado. This spiral formation and the separation

3.The lighter components of this gas have less inertia, so it is easier for them to be influenced by the vortex and travel up it. Contrarily, larger components of particulate matter have more inertia and are not as easily influenced by the vortex

4.Since these larger particles have difficulty following the high-speed spiral motion of the gas and the vortex, the particles hit the inside walls of the container and drop down into a collection hopper.

6.These chambers are shaped like an upside-down cone to promote the collection of these particles at the bottom of the container. The cleaned flue gas escapes out the top of the chamber.

7.Most cyclones are built to control and remove particulate matter that is larger than 10 micrometers in diameter. However, there do exist high efficiency cyclones that are designed to be effective on particles as small as 2.5 micrometers. As well, these separators are not effective on extremely large particulate matter. For particulates around 200 micrometers in size, gravity settling chambers or momentum separators are a better option.

Empirical models used to calculate the cyclone separator :

1) Iozia and Leith Model

Iozia and Leith logistic model 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)Koch and Licht Mode:

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 describedparticle motion in the entry and collection regions with the ad- 200
ditional following assumptions:

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 u Rn = constant.
Aforce balance and an equation on the particles collection yields
the grade efficiency

3) Li and Wang Model:
1.The Li and Wang model includes particle bounce or reentrainment and turbulent diffusion at the cyclone wall.

2.A twodimensional analytical expression of particle distribution in thecyclone is obtained.

3.Li and Wang model was developed based on the following assumptions:

Assumptions:

• The radial particle velocity and the radial concentrationprofile are not constant for uncollected particles within
the cyclone.
• Boundary conditions with the consideration of turbu185 lent diffusion coefficient and partic bounce reentrainment on the cyclone wall are:
c = c0, at θ = 0

Dr ∂c/∂r= (1 − α)wc, at r = D/2

The tangential velocity is related to the radius of cyclone by: u Rn = constant.
The concentration distribution in a cyclone is given as:

4)Lapple Model
1.Lapple model was developed based on force balance without considering the flow resistance.

2.Lapple assumed that a particle entering the cyclone is evenly distributed across the inletopening.

3.The particle that travels from inlet half width to thewall in the cyclone is collected with 50% efficiency.

4.The semiempirical relationship developed by Lapple to calculate a
50% cut diameter, dpc, is

Procedure:

1)Geometry:

1.Import cyclone separator file to ansys fluent

2.Exract fluid from the solid

Mesh :

1)Used structural mesh for this model to reduce the time period and also reduce the no of elements

2)Name the boundary and intial conditions.

Setup :

CASE 1:

Velocity -3m/s

particle size - 1 microns

residual

results

Pressure contour :

Velocity contour

CASE 2:

Velocity - 3m/s

particle size - 3 microns

Velocity contour :

Pressure contour :

Case 3

velocity - 3m/s

particle size - 5 microns

velocity

Pressure contour

Dpm :

Case 4

velocity - 1 m/s

particle size - 5m/s

pressure :

velocity :

Case 5 :

Velocity - 5 m/s

Particle size - 5 microns

Pressure contour

velocity :

videos files for all the cases :

Comparison table of cyclone seperator efficiency and also the pressure drop :

Efficiency of the cyclone - No.of particles trapped /no.of particles tracked.

Sl.no	Velocity (m/s)	Particle size (micro metres)	Particle tracked	Particle escaped	Particle trapped	Efficiency	Inlet pressure(Pa)	Outlet trap pressure(pa)	Pressure drop(pa)
1	3	1	378	72	306	80.95%	24.69	3.11	21.58
2	3	3	378	76	300	79.36%	23.43	3.22	20.21
3	3	5	378	133	245	64.81%	23.98	2.01	21.58
4	1	5	378	66	312	82.53%	2.50	0.297	2.203
5	5	5	378	76	302	79.89%	68.76	9.34	59.35

conclusion :

1)The efficiency of the cyclone seperator is totally depend upon the velocity of the fluid and also the size of the particles.

2)If the velocity is low with high particle size then the efficiency of the cyclone seperator is high

3)If the velocity is low and the particle size is high then the efficiency of the cyclone seperator is low

4)efficiency of the cyclone seperator is totally depend upon the velocity with respect to the particle size.