1 OBJECTIVE

Calculate separator efficiency & pressure drop at constant velocity of 3m/s & vary particle size from 1micron to 5 microns. Later on, keep particle size constant at 5micron & vary particle velocity from 1 m/s to 5m/s & recalculate pressure drop &efficiency.

2 INTRODUCTION

Role of separators are very important when we talk about gas cleaning system. These components have been extremely used in industries which are involved with removing dusts, collecting microparticles, cleaning equipment, biosensors, and air purification systems. Due to large scope of separators different construction has been done which utilises type of force for separation which involves centrifugal acceleration, gravity, & inertia. The most important application of cyclones is to remove industrial dust from air or may be from any of the processing gasses. The mainly used type of separator are either gas-solid or gas-liquid separator. Cyclones are simple in construction &economical & having ability to operate on higher side of temperature &pressure. A cyclone separator working principle is based on particle settling by centrifugal force. A cyclone separator is a device that makes mixture flow into the inlet, generates a cyclone, and separates particulates from a gas, air or liquid stream by the use of centrifugal force. During this phenomenon a vortex generation takes place inside the cyclone which helps in transferring the inertia force of gaseous particle into to centrifugal force. Centrifugal force is a result of increasing air velocity in outer vortex. When the air reaches the bottom of the cone, it begins to flow radially inwards and out the top as clean air/gas while the particulates fall into the dust collection chamber attached to the bottom of the cyclone. Settling of particles is heavily dependent on inside velocity of cyclone separator. Higher the velocity, more the settling. Hydro cyclone is used while separating particulates matter from liquid & gas cyclone is used while removing particles from gas. Rotational effect and gravity are used to separate mixtures of solids and fluids. Fine droplets of liquid can also be separated using same concept from the mixture of gaseous stream. Variety of cyclones can be found for the separation of solid particles but most widely used type of are- returned flow or reversed flow, axial flow and rotary flow with tangential injection of the second gas flow into the cyclone body.

Following are some basic empirical models used to calculate the cyclone separator efficiency

• Iozia and Leith Model

It is a modified version of barth model & based on force balance. It consider the effect of centrifugal force & flow resistance.Dirgo and Leith (1985) developed an optimization program to investigate design changes that would improve performance. Subsequently, Iozia and Leith (1990) developed an improved method to predict cyclone aerodynamic cut diameter, d50. Aerodynamic cut diameter is the particle size collected with 50% efficiency.

• Li and Wang Model

This model includes particles bound & turbulent diffusion at cyclone wall. There were some assumption in this model.

The radial particle velocity and the radial concentration profile are not constant for uncollected particles within the cyclone. The tangential velocity is related to the radius of cyclone by:

u Rn = constant.

• Koch and Licht Model

This model focuses on turbulence nature of cyclone & distriution of gas residence time within cyclone.They also focused on particle in entry & collection region. There was following assumption in this model

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 & gas.

• Lapple Model

This model was also based on force balance but they did not consider any flow resistance. Lapple assumed that 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.

3 GEOMETRY & MESHING

3.1 GEOMETRY

Following geometry shows the detailed geometry of cyclone separator. Detailed nomenclature has been done for component. There are 2 outlets & only one inlet. Outlet at the top is responsible for giving clear air & the lower outlet gives the dirt particles. Dust collector is present at dirt outlet.

Following figure shows proper dimensions nomenclature

3.2 MESHING

Automatic meshing has been done with a change in element size. The element size was kept as 5mm. This resulted in 112208 number of nodes & 578281 number of elements. Below figure shows the meshing of component

4 BOUNDARY CONDITION

Total 10 times simulation has been done to conclude the topic. First 5 simulation has been done at constant velocity of 3 m/s & particle size was monitored from 1micron to 5 micron, & next 5 simulation was done at constant particle size of 5 micron & velocity was monitored from 1m/s to 5m/s.

The inlet & wall was kept as reflector, top outlet was given as escape where clear gasses comes out & the bottom outlet was given as trap where dirt gets collected. This boundary condition was common in all 10 simulation.

5 PHYSICS & SETUP

K-epsilon RNG turbulence model was used because it gives best prediction of swirling flow & in cyclone separator swirling effect can’t be neglected. Simple scheme was used for pressure velocity coupling. For the discretisation of pressure term, second order discretisation method has been chosen. Momentum & turbulence quantity has been discretisation with the help of second order upwind scheme.

Discrete phase has been kept on for this simulation. This helps in tracking the trajectory of particles & maintaining DPM boundary condition as discussed in boundary condition section 4. Maximum number of steps was 50000 & step length factor was 5. Inert particle type has been maintained & material chosen was anthracite. Injection type was surface at inlet.

6 RESULT & DISSCUSION

6.1 RESIDUE

Following plot shows the residue. Simulation was run for 600 iteration in all 10 cases & nature of residue was found to be similiar in each cases.

6.2 EFFICIENCY

6.2.1 EFFICIENCY AT CONSTANT PARTICLE SIZE

Following table shows the particle history at constant particle size. The fractional value of efficiency can be calculated by dividing trapped number by tracked number of particles.

VELOCITY	TRACKED	ESCAPED	TRAPPED	INCOMPLETE	EFFICIENCY
m/s	count	count	count	count	fraction
1	438	94	105	239	0.2397
2	438	29	37	372	0.0844
3	438	21	25	392	0.0570
4	438	13	168	256	0.3835
5	438	29	372	37	0.8493

6.2.2 EFFICIENCY AT CONSTANT VELOCITY

Following table shows the particle history at constant velocity. The fractional value of efficiency can be calculated by dividing trapped number by tracked number of particles.

SIZE	TRACKED	ESCAPED	TRAPPED	INCOMPLETE	EFFICIENCY
micron	count	count	count	count	fraction
1	438	108	88	242	0.20
2	438	94	75	269	0.17
3	438	61	58	319	0.13
4	438	39	33	364	0.075
5	438	21	25	392	0.057

6.3 PRESSURE DROP

6.3.1 PRESSURE DROP AT CONSTANT PARTICLE SIZE

Following table shows the pressure at inlet, & both outlets. The pressure difference was calculated using calculating the difference in pressure of inlet & outlet. The particle size was kept constant at 5micron & velocity was monitored

CASE	VELOCITY	PRESSURE-INLET	PRESSURE-OUTLET1	PRESSURE-OUTLET2	PRESSURE-DROP Outlet-1	PRESSURE-DROP Outlet- 2
unit	m/s	Pascal	Pascal	Pascal	Pascal	Pascal
1	1	1.1735	0.2876	0.1761	0.8859	0.9974
2	2	7.7619	0.9041	1.0793	6.8578	6.6826
3	3	18.6561	2.4157	2.5442	16.2404	16.1119
4	4	34.5938	4.6209	4.2948	29.9729	30.2990
5	5	55.6376	7.9226	6.0568	47.715	49.5805

6.3.2 PRESSURE DROP AT CONSTANT VELOCITY

Following table shows the pressure at inlet, & both outlets. The pressure difference was calculated using calculating the difference in pressure of inlet & outlet. The velocity was kept constant at 3m/s & particle size was monitored

CASE	PARTICLE SIZE	PRESSURE-INLET	PRESSURE-OUTLET1	PRESSURE-OUTLET2	PRESSURE-DROP Outlet-1	PRESSURE-DROP Outlet- 2
unit	micron	Pascal	Pascal	Pascal	Pascal	Pascal
1	1	18.6561	2.4157	2.5442	16.2404	16.1119
2	2	18.6561	2.4157	2.5442	16.2404	16.1119
3	3	18.6561	2.4157	2.5442	16.2404	16.1119
4	4	18.6561	2.4157	2.5442	16.2404	16.1119
5	5	18.6561	2.4157	2.5442	16.2404	16.1119

6.4 PLOTS

6.4.1 PRESSURE-PLOT

6.4.1 TURBULENCE

7 CONCLUSION

7.1 EFFICIENCY

We have discussed about efficiency in section 6.2. There are 2 tables showing particles history for all 10 cases. We can conclude that efficiency keeps on decreasing continuously if particle size keeps on increasing from 1micron to 5microns at constant velocity of 3m/s.

But if particle size is kept constant at 5micron & velocity was increased from 1m/s to 5m/s in step of 1m/s then efficiency decreases up to 3m/sec & after that started increasing up to 5m/sec.

7.2 PRESSURE DROP

When inlet velocity was kept constant at 3m/sec there was a constant pressure drop in all 5 cases. It means pressure doesn’t depend on particle size. It is a function of velocity only.

But when velocity was increased from 1m/s to 5m/s at constant particle size it has been observed that the inlet pressure kept increasing continuously. Pressure at both outlets kept increasing & as a result pressure drop also kept increasing.

IT CAN BE CONCLUDED THAT WITH INCREASE IN PRESSURE DROP, EFFICIENCY KEPT DECREASING UP TO 3m/s & STARTED INCREASING TILL 5m/s.