To perform an analysis of the cyclone separator in Ansys Fluent

Title:  To perform an analysis of the cyclone separator 

Objective:

1.To Perform an analysis of the given cyclone separator model by varying the particle diameter from 1 µm to 10 µm.

2. To calculate the separation efficiency in each case by varying the particle diameter from 1 µm to 10 µm.

3.To calculate the separation efficiency and pressure drop by varying the inlet velocity of both fluid and particle from 5 m/sec to 20 m/sec .

Theory

Cyclone separator

              Cyclone separators, which separate dispersed solid particles from a fluid suspension by centrifugal and vortex action, have played an important role in industry for the separation and recovery of fine particles. For a cyclone separator, collection efficiency and pressure losses are the main performance characteristics.

Cyclones are devices that employ a centrifugal force generated by a spinning gas stream to separate particles from the carrier gas. Their simple design, low maintenance costs, and adaptability to a wide range of operating conditions such as sizes and flow rates make cyclones one of the most widely used particle removal devices. By using suitable materials and methods of construction, cyclones may be adapted for use in extreme operating conditions: high temperature, high pressure, and corrosive gases. Cyclones are important particle removal devices in both engineering and process operations.

              An inaccuracy in cyclone efficiency prediction may result in an inefficient design of cyclone separators. Models to predict the behaviour of cyclones are usually empirical. It remains largely a process of trial and error, since empirical cyclones models are only applicable to specific cyclone geometries. 

            The most common design for a cyclone separator is termed the reverse-flow or cone-under-cylinder design, as is shown in Figure . The straight-through design works on the same principal as the reverse-flow design but uses swirl vane entries to rotate the gas. However, these straight-through designs are rarely used in industry and little data is available on them.

                                       

Empirical models used for cyclone separator efficiency

1.IOZIAAND LEITH MODEL
                 Iozia and Leith (1990) logistic model is a modified version of Barth (1956) 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. Core length, zc, and core diameter, dc, are given as.

                             

The addition made by Iozia and Leith on the original Barth (1956) model are the core length zc and slope parameter beta expression which is derived based on the statistical analysis of
experimental data of cyclone with D = 0.25 m. The collection efficiency of particle diameter dpi can be calculated from.

                               

2.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 tangential velocity is related to the radius of cyclone by:
                        uRn = constant.

The concentration distribution in a cyclone is given as

               

                                               

                                                         

The resultant expression of the collection efficiency for particle
of my size is given as

                                           

                                         

3.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 Licht describe 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 cyclone by: uRn = constant.

    A force balance and an equation on the particles collection yields the grade efficiency hi.

                             

                                                 

G is a factor related to the configuration of the cyclone, n is related to the vortex and t is the relaxation term.

4.LAPPLE MODEL

Lapple (1951) 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. The semi empirical relationship developed by Lapple (1951) to
calculate a 50% cut diameter, dpc, is

                                       

where Ne is the number of revolutions

                                         

The efficiency of collection of any size of particle is given by

                                           

Nomenclature

L = natural length (m)
a = cyclone inlet height (m)
b = cyclone inlet width (m)
D = cyclone body diameter (m)
De = cyclone gas outlet diameter (m)
H = cyclone height (m)
h = cyclone cylinder height (m)
S = cyclone gas outlet duct length (m)
B = cyclone dust outlet diameter (m)
c0, c1 = particle inlet and outlet concentration (kg/m3)
d = particle diameter (m)
Dr = radial turbulent diffusion coefficient
dpc = cut particle diameter collected with 50%
efficiency (m)
n = cyclone vortex exponent (0.5 < n < 1)
Q = volumetric gas flow rate (m3/s)
r = radial dimension, rw = D/2 and rn = De/2 (m)
R = radius (m)
T = absolute temperature (K)
w = radial particle velocity (rad/s)
wn, ww = radial particle velocity at r = rn and r = rw(rad/s)

Given solid Volume of Cyclone separator   

 

Fluid Volume extracted in spaceclaim of cyclone separator model

Mesh 

Element size uses 6mm , for fine mesh to get good result near wall there is add inflation layer 5 with growth rate 1.2

Setup made for simulation

1. State>=Steady state

2.Gravity>= y(m/s2)=-9.81

3. Viscous model>K-epsilon>RNG>Swril dominated flow

4. Physic> Discrted phase model>interact with cont. phase>update DPM source                        every flow iteration 

5.Tracking>Max.No.of step>50000

6. Step length factor>5

7.Inection type>surface>injection materail>anthracite

8. Solution method> Preesure, momentum, turbulent disspation rate, Turbulent kinetic                                    energy>Secon order upwind.

9.Boundary Conditions:

    Inlet & Wall:- Reflect

    Outlet_dustbin (Bottom):- Trap  

    Outlet (Top):- Escape

10. Intialize method > standard> form inlet

11. Iteration for simulation>600

Part-I: Vary the particle diameter from 1-10μm & Constant inlet both velocity 3m/s

In  this part vary the particle diameter 1, 3,6,9μm  & keep constant both particle & inlet velocity 3m/s & measure the Cyclone efficiency. So,it divide in to four cases.

Cases-I: Particle diameter 1μm & constant both velocity  3m/s

Residual plot

there use of 600 iteration to run the simulation, so after 500 iteration solution is converged

Particle time

from above graph we can see that less no. of particle is escaped from top outlet , where maximum particle trap in bottom outlet.

Vortex core

vortex core shows that, swirl or  vortex effect is generated & which help for trap the more particle.

Cases-II: Particle diameter 3μm & constant both velocity  3m/s

Residual plot

particle time

from above graph we can see that less no. of particle is escaped from top outlet , where maximum particle trap in bottom outlet

Vortex core

Cases-III: Particle diameter 6μm & constant both velocity  3m/s

Residaul plot

there use of 600 iteration to run the simulation, so after 500 iteration solution is converged

Particle time

from above graph we can see that less no. of particle is escaped from top outlet , where maximum particle trap in bottom outlet

Vortex core

vortex core shows that, swirl or  vortex effect is generated & which help for trap the more particle.

Cases-IV: Particle diameter 9μm & constant both velocity  3m/s

Residaul plot

Particle time

Vortex core

Part-II: Vary the inlet both velocity 5-20m/s & Constant particle diameter 5μm 

            In  this part vary the both particle & inlet velocity 5-20m/s  & keep constant particle diameter 5μm  &  measure the Cyclone efficiency & pressure drop. So,it divide in to four cases.

Cases-I: Both inlet velocity 5 m/s & keep constant Particle diameter 5μm 

Residaul plot

there use of 600 iteration to run the simulation, so after 500 iteration solution is converged

Pressure variation 

from pressure plot we can say that , maximum pressure at inlet & less pressure at outlet dustbin

vortex core

vortex core shows that, swirl or  vortex effect is generated & which help for trap the more particle.

Cases-II: Both inlet velocity 10 m/s & keep constant Particle diameter 5μm 

Residaul plot

 

Pressure variation 

Vortex core with pressure

Cases-III: Both inlet velocity 15 m/s & keep constant Particle diameter 5μm

Residual plot

 

Pressure variation

Vortex core with pressure

Cases-IV: Both inlet velocity 20 m/s & keep constant Particle diameter 5μm

Residual plot

Pressure variation

Vortex core with pressure

Part-I: Output Result table

Cyclone efficiency =Trapped particle/ Tracked particle

                            = 2017/448=46.20%

Part-II: Output Result table

Sample calculation

Preesure drop = presure inlet- Pressure outlet_dustbin

                      =46.61- 0.007637 =46.60 pa

Part-I: Final Result Graph

From above  graph we can see that as particle diameter is increase , there is increase the cyclone efficiency & its because of the as increase particle size  which is easily trapped & so that efficency increase

Part-II: Final Result Graph

From above graph its observe that as velocity increase  there is increase the cyclone efficiency & its becasue of the as increase the velocity there is swirl effect is developed which help to trapp the particle easily as compare to small particle.

 

 from above graph its observed that as increase the velocity there increase the cyclone efficiency but its also truth that there is increase the pressure drop. pressure drop is affect on cyclone efficiency.

Overall conclusion

1. As particle diameter increase the cyclone efficiency  increase & its because of the increase diameter of particle which easily trapped.

2. As increase the velocity there  is increase the cyclone efficiency & its becasue of swirl effect , which help to easily trap the particle.

3. As there increase the velocity there is increase the Pressure drop, which affect on cyclone efficiency.

4. Cyclone separator is gives higher cyclone efficiency.