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:-
- To write a few words about any four empirical models used to calculate the cyclone separator efficiency.
- 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.]
- 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 matter from flue gases
2.Cyclone separators is one of many air pollution controlling devices known as pre-cleaners 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 Model for Cyclone efficiency
Model 1: Iozia and 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 flow resistance, W. Core length, zc, and core diameter, dc are given as:
β is an expression for slope parameter derived based on the
statistical analysis of experimental data of a cyclone with D = 170
0.25 m given as:
and dpc is the 50% cut size given by Barth:
where core length, zc, and core diameter, dc, are given as
Model 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
- The profile is not constant for uncollected particles within the cyclone.
Boundary conditions with the consideration of turbulent diffusion coefficient and particle bounce entrainment on the cyclone wall are:
Model 3: Koch and Licht Model
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 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.
A force balance and an equation on the particles collection yields
the grade efficiency ηi:
Model 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. The semi-empirical relationship developed by Lapple [1] to calculate a 50% cut diameter, dpc, is:
PROCEDURE
the following procedure is followed in performing the simulation and extracting the results
1. Geometry Setup:
- Import the given geometry in SpaceClaim
- Extract the fluid volume from the geometry. Prepare -> extract volume -> select edges
- Suppress the given geometry for physics.
2. Mesh setup:
Mesh stats:
1. Main element size: 5 mm
2. Method = Cartesian method
3. Cartesian element size= 5 mm
Named selections are assigned to identify the inlets and outlets of the domain
3 - Setting up Physics:
- Pressure based, steady-state solver. Gravity = - 9.81 m/s2 in Y- Axis
- Model: K-Epsilon -> RNG, Swirl Dominated Flow
- Model: Discrete Phase model -> Interaction with continuous phase, update DPM sources every flow iteration, Max no of steps -> Create Injections
Boundary Conditions: Inlet -> velocity, DPM = reflect, Outlet top -> DPM = escape, Outlet bottom -> DPM = trap, walls -> DPM = reflect
4: Method:
Result:
Case 1 (a): Veiocity- 3m/s & Diameter- 1e-6 m
Residual Plot:
Separation Efficiency in % = (299 / 378) * 100
Separation Efficiency = 79.10%
Pressure contour & Pressure drop
Max Pressure = 26.46 pa, Min Pressure = -4.26 Pa
Pressure Difference = 30.72 Pa
Case 1 (b): Veiocity- 3m/s & Diameter- 2e-6 m
Residual Plot:
Separation Efficiency in % = (303 / 378) * 100
Separation Efficiency = 80.15%
Pressure contour & Pressure drop
Max Pressure = 26.4551 pa, Min Pressure = -4.2577 Pa
Pressure Difference = 30.7128 Pa
Case 1 (c): Veiocity- 3m/s & Diameter- 3e-6 m
Residual Plot:
Separation Efficiency in % = (308 / 378) * 100
Separation Efficiency = 81.48%
Pressure contour & Pressure drop
Max Pressure = 26.4551 pa, Min Pressure = -4.2577 Pa
Pressure Difference = 30.7128 Pa
Case 1 (d): Veiocity- 3m/s & Diameter- 4e-6 m
Residual Plot:
Separation Efficiency in % = (292 / 378) * 100
Separation Efficiency = 77.24%
Pressure contour & Pressure drop
Max Pressure = 26.4551 pa, Min Pressure = -4.2577 Pa
Pressure Difference = 30.7128 Pa
Case 1 (e): Veiocity- 3m/s & Diameter- 5e-6 m
Residual Plot:
Separation Efficiency in % = (262 / 378) * 100
Separation Efficiency = 69.31%
Pressure contour & Pressure drop
Max Pressure = 26.4551 pa, Min Pressure = -4.2577 Pa
Pressure Difference = 30.7128 Pa
| Case 1 | Size of Particles (m) | Velocity of particles (m/s) | No of the particles tracked | No of the particles escaped | No of the particle trapped | No of the particles incomplete | separation efficiency (%) | Pressure difference (Pa) |
| 1 | 1e-6 | 3 | 378 | 79 | 299 | 0 | 79.1 | 30.72 |
| 2 | 2e-6 | 3 | 378 | 75 | 303 | 0 | 80.15 | 30.72 |
| 3 | 3e-6 | 3 | 378 | 70 | 308 | 0 | 81.48 | 30.72 |
| 4 | 4e-6 | 3 | 378 | 86 | 292 | 0 | 77.24 | 30.72 |
| 5 | 5e-6 | 3 | 378 | 116 | 262 | 0 | 69.31 | 30.72 |
Case 2 (a): Veiocity- 1m/s & Diameter- 5e-6 m
Residual Plot:
Separation Efficiency in % = (312 / 378) * 100
Separation Efficiency = 82.53%
Pressure contour & Pressure drop
Max Pressure = 2.5038 pa, Min Pressure = -0.7011 Pa
Pressure Difference =3.2049 Pa
Case 2 (b): Veiocity- 2m/s & Diameter- 5e-6 m
Residual Plot:
Separation Efficiency in % = (287 / 378) * 100
Separation Efficiency = 75.92%
Pressure contour & Pressure drop
Max Pressure = 11.4213 pa, Min Pressure = -2.0236 Pa
Pressure Difference = 13.4447 Pa
Case 2 (c): Veiocity- 4m/s & Diameter- 5e-6 m
Separation Efficiency in % = (257 / 378) * 100
Separation Efficiency = 67.98%
Max Pressure = 47.6832 pa, Min Pressure = -7.1954 Pa
Pressure Difference =54.8786 Pa
Case 2 (c): Veiocity- 5m/s & Diameter- 5e-6 m
Separation Efficiency in % = (291 / 378) * 100
Separation Efficiency = 76.98%
Max Pressure = 76.0179 pa, Min Pressure = -10.8218 Pa
Pressure Difference =86.8397 Pa
| Case 2 | Size of Particles (m) | Velocity of particles (m/s) | No of the particles tracked | No of the particles escaped | No of the particle trapped | No of the particles incomplete | separation efficiency (%) | Pressure difference (Pa) |
| 1 | 5e-6 | 1 | 378 | 66 | 312 | 0 | 82.53 | 3.2049 |
| 2 | 5e-6 | 2 | 378 | 91 | 287 | 0 | 75.92 | 13.4447 |
| 3 | 5e-6 | 3 | 378 | 116 | 262 | 0 | 69.31 | 30.72 |
| 4 | 5e-6 | 4 | 378 | 121 | 257 | 0 | 67.98 | 54.8786 |
| 5 | 5e-6 | 5 | 378 | 87 | 291 | 0 | 76.98 | 86.8397 |