Fa-Gung Fan is modeling and simulating the filtration of micro-sized particles by micro-pillar structures using Fluent software. The objectives are to evaluate filtration efficiency, capacity, and pressure drop over time for different filter designs. Fluent's Macro-Particle Model is used to simulate particle motion, collisions, and deposition. Several filter designs are evaluated and their performance is compared.

1. Fa-Gung Fan
Modeling Particle
Capturing/Filtration
4/6/2012
Fa-Gung Fan
fagung@gmail.com

2. Fa-Gung Fan
Objectives
• Model and simulate rigid, spherical micro-
particles filtration by micro-sized pillar
structures.
• Evaluate the filtration efficiency/capacity of
different filter structures.
• Evaluate the pressure drop vs. time.

3. Fa-Gung Fan

4. Fa-Gung Fan
Physics
• Laminar flow
• Particle motion
• Flow blockage and momentum exchange
• Particle-particle and particle-wall collisions
• Particle deposition and buildup

5. Fa-Gung Fan
Fluent Macro-Particle Model (MPM)
• Flow simulation is carried out with Fluent
software.
• MPM is a module attached to standard Fluent
code.
• Particle motion, particle-particle/particle-wall
collisions, particle buildup are handled by
MPM module.
• Filter structure is modeled with body-fitted
mesh (in Fluent), whereas particles are
modeled with immersed-boundary method (in
MPM).

6. Fa-Gung Fan
Fluent Macro-Particle Model (MPM)
Account for:
• Flow blockage and momentum exchange
• Drag and torque on particles
• Particle-particle and particle-wall collision and
friction dynamics
• Particle deposition and buildup

7. Fa-Gung Fan
MPM Technical Approach

8. Fa-Gung Fan
• Fluent/MPM provides the most comprehensive
capability with respect to the modeling needs.
• However, MPM was originally developed for
oil/gas industry. Had not been used in micro-
filtration application before.
• Collision detection algorithm was not optimized
for micro-scale features.
• Had to worked with Fluent developer for about
two months to improve the algorithm.
• ANSYS/Fluent extended the software license for
2.5 months to compensate for the lost time.
Software Choice

9. Fa-Gung Fan
z
x
d
rz
rx
Design x z rx rz d
Ov1 184 60 50 25 20
Ov2 184 100 50 25 20
Ov3 240 100 50 25 20
Designs (Ov1, Ov2, Ov3, Ov4)

10. Fa-Gung Fan
• Ov4 is a case of narrow channel, truncated from Ov3 by taking only a single
oval-shaped structure.
Ov3 Ov4
Ov1
These are actually ovals (like
those in Ov1). The figures
do not preserve aspect ratio
so they look like circles.
Ov1

11. Fa-Gung Fan
Ov1 design
Unit Cell

12. Fa-Gung Fan
Ov1
Reached stationary state.
# of particles captured in
one unit cell
Ov1 Design: unit cell area 184umx120um, captures 150 particle per unit cell
Total 4060 particles injected.
Capture Efficiency / Capture Capacity

13. Fa-Gung Fan
Ov3 # of particles captured in
one unit cell
Reached stationary state.
Ov3 Design: unit cell area 240umx200um, captures 150 particles per unit cell

14. Fa-Gung Fan
Pressure Drop Comparison
Ov3 Ov4Ov1

15. Fa-Gung Fan
10mm
10mm
A 10mmx10mm chip can fit –
54x83 Ov1 unit cells. Total capture capacity: 672300 particles/chip
54x50 Ov2 unit cells. Total capture capacity: 432000 particles/chip
41x50 Ov3 unit cells. Total capture capacity: 307500 particles/chip

16. Fa-Gung Fan
Particle number density profile
Unit Cell
Depending on the capture efficiency of the unit
cells, the speed of propagation varies.
z
Propagation of Density Profiles
A uniform density profile propagates down a series of 50 unit cells (each 0.2mm
length in the z direction). The following animation shows the propagations of
the profiles (corresponding to 40% solid loadings) for unit cell capture
capacities of 0, 150, 550, and 3000 particles and a fluid flow speed of 0.05m/s.
It can be seen that, when the unit cell does not capture particle at all, the
propagation of the density profile is fastest. As the unit cell capture capacity
increases, the propagation speed decreases. At the limit of very large capture
capacity, the wave does not propagate down the unit cells, which means that all
the particles are captured by the first unit cell.

17. Fa-Gung Fan
Ov1 Ov2 Ov3
Density profiles (correspond to 40% solid loadings) at t=0.2 sec

18. Fa-Gung Fan
Particle Loading Sensitivity
Ov3 (inject 5 particles every 8.e-5 sec)
Ov3 Design: unit cell area 240umx200um, captures 150 particles per unit cell

19. Fa-Gung Fan
Ov3 (inject 10 particles every 8.e-5 sec)
Ov3 Design: unit cell area 240umx200um, captures 150 particles per unit cell
Total 5810 particle injected.
Note: This animation runs fast.

20. Fa-Gung Fan
Ov3 (inject 20 particles every 8.e-5 sec)
Ov3 Design: unit cell area 240umx200um, captures 175 particles per unit cell

21. Fa-Gung Fan
Conclusions
• Direct simulations of filtration of rigid,
spherical micro-particles by micro- filter
structures have been carried out.
• The simulations provide information about
filtration/capturing efficiency, capturing
capability, and pressure drop.
• Several filter structures were evaluated
and their capturing/filtration effects and
pressure drops were compared.

22. Fa-Gung Fan
• Sensitivity to particle loading was also
studied. The result indicates that
simulations need to be carried out at
actual particle loadings.
• Fluent/MPM platform provides the most
comprehensive capability for the work.