1. Particle Resuspension Model for Indoor Air Quality Applications
Goodarz Ahmadi
Clarkson University

2. Outline Motivation and Objectives
Adhesion & Detachment of Particles with elastic & Plastic deformation
Particle Adhesion & Detachment with Capillary & Electrostatic Forces
Particle Removal from Rough Surfaces:
Small Roughness
Bumpy Particles
Highly Rough Surfaces
Particle Removal due to Human Walking
Model Description
Sample Results
Conclusions and Future work

3. Motivation and general Objectives
Concentrations of particle pollutants in the indoor environment are often higher than outdoor. Particle resuspension due to human activity is expected to be one cause for the increase in PM.
Primary goal of this thrust is to provide quantitative understanding of the contribution of particle resuspension to PM concentration in the indoor environment

4. Specific Objectives
Develop a particle detachment/re-suspension model for spherical and non-spherical particles from surfaces in the presence of capillary and electrostatic forces for indoor air quality applications.
To validate the detachment/re-suspension model.
To Develop a user defines subroutine for implementation of the model in the CFD codes.
To asses the contribution of the resuspension to the increase in indoor PM concentration due to human activities.

5. Particle Resuspension from Smooth Surfaces
Forces Acting on a Particle
Rolling Detachment
Elastic and Plastic Deformations

6. JKR Adhesion Model Maximum Resistance to Rolling
Thermodynamic Work of Adhesion
Composite Young Modulus

7. DMT and Maugis-Pollock Adhesion Model
Maximum Resistance to Rolling (DMT)
Maximum Resistance to Rolling (MP)

8. Particle Resuspension
Model Predictions Results
Polystyrene-Polystyrene
Burst, Rolling
JKR
DMT
Maugis-Pollock
d (μm)
Critical shear velocities for particle resuspension as predicted by different adhesion models.

9. Particle Resuspension
Model Predictions Results
d (μm)
Calcium Carbonate-
Calcium Carbonate
Burst, Rolling
With Capillary
JKR
DMT
Maugis-Pollock
Critical shear velocities for particle resuspension as predicted by different adhesion models.

10. Particle Resuspension
Model Predictions Results
d (μm)
Glass-Glass
Burst, Rolling
JKR
DMT
Maugis-Pollock
With Capillary
Without Capillary
□ Taheri and Bragg [39]
○ Ibrahim et al. [40]
Comparison of the model predcition with the experimental data of Taheri and Bragg [39] (□) and Ibrahim et al. [40] (○).

11. Particle Resuspension
Model Predictions Results
d (μm)
Glass-Steel
Burst, Rolling
JKR
DMT
Maugis-Pollock
With Capillary
Without Capillary
□ Zimon [38]
○ Ibrahim et al. [40]
◊ Ibrahim et al. [41]
Comparison of the model predictions with the experimental data of Zimon [38] (□), Ibrahim et al. [40] (○) and Ibrahim et al. [41] (◊).

12. Resuspension of Rough Particles
Rough Surface
Rough Particle mg mg

13. Resuspension of Rough Particles
Comparison of the critical shear velocities as predicted by the burst model with the experimental data of Zimon [38]

14. Bumpy Particles
Bumpy particle model of compact irregular particles

15. Electrostatic Forces for Bumpy Particles
Charge
Hays

16. Bumpy Particles
Critical shear velocities for bumpy particle resuspension in the presence of capillary and electrostatic forces.

17. Bumpy Particles
Critical shear velocities for bumpy particle resuspension in the presence of capillary and electrostatic forces.

18. Bumpy Particles
Critical shear velocities for bumpy particle resuspension in the presence of capillary and electrostatic forces.

19. Bumpy Particles
Critical shear velocities for bumpy particle resuspension in the presence of capillary and electrostatic forces.

20. Bumpy Particles
Comparison of the critical electric field with the experimental data of Hays (1978)

21. Resuspension form Highly Rough Surfaces
Adhesion Force
Hydrodynamic Forces

22. Sample Surface and Airflow
Velocity (m/s) Contours over a Randomly generated surface with a roughness value of 5 micron.

23. Sample Particle Removal

24. Removal Areas for 2.5 µm Particles
V = 5 m/s

25. Particles Pairs Removal

26. A Model for Particle Resuspension by Walking
Assumptions
Shoe floor contact is modeled as two circular disks.
Squeezed film and wall jet models are used for the air low velocity.
Step down and up in the gait cycle are treated.
Particle re-deposition is accounted for.

27. Evaluation of Squeezing Velocity
Inside Foot Area (r < R)
Outside Foot Area (r > R)

28. A Model for Particle Resuspension by Walking
Squeezed Film
Wall Jet
Critical radius for particle detachment for rolling detachment mechanisms at stepping down process.

29. Particle Resuspension
__ Simulation d=3~4μm
x--- Experiment d=3~4μm
__ Simulation d=5~7.5μm
*--- Experiment d=5~7.5μm
h=2.3
t (min)
Comparison of the predicted particle concentration with the experimental data of Ferro and Qian (2006) for hard floor.

30. Conclusions
A particle resuspension model from smooth and rough surfaces in presence of capillary force and electrostatic forces was developed.
The model was applied to particle resuspension in indoor environment due to human activities.
Preliniary comparisons with experimental data was performed.

31. Future Work Validate the model against additional data.
Perform detailed analysis of particle resuspenion in indoor environment due to human activities.
Develop detailed effect of large surface roughness on particle resuspension.
Develop a user defines subroutine for implementation of the model in the CFD codes.
Develop a model for resuspension form carpeted surfaces.