Particle Resuspension Model for Indoor Air Quality Applications Goodarz Ahmadi Clarkson University ahmadi@clarkson.edu

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

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

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.

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

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

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

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.

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.

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] (○).

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] (◊).

Resuspension of Rough Particles Rough Surface Rough Particle mg mg

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

Bumpy Particles Bumpy particle model of compact irregular particles

Electrostatic Forces for Bumpy Particles Charge Hays

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

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

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

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

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

Resuspension form Highly Rough Surfaces Adhesion Force Hydrodynamic Forces

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

Sample Particle Removal

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

Particles Pairs Removal

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.

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

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

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.

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.

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.