AN INVESTIGATION OF WALKING INDUCED ELECTROSTATIC FIELD EFFECTS ON INDOOR PARTICLE RESUSPENSION
Open Access
- Author:
- Hu, Bin
- Graduate Program:
- Architectural Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 29, 2007
- Committee Members:
- James Freihaut, Committee Chair/Co-Chair
Stanley Allan Mumma, Committee Member
William P Bahnfleth, Committee Member
James Landis Rosenberger, Committee Member - Keywords:
- particle resuspension
walking
electrostatic effect
indoor environment - Abstract:
- Airborne concentration of particulate matter (PM) is an important index of indoor air quality. Researches have demonstrated the strong correlation between airborne particulate concentration and human health. Micron-sized particulate sources are commonly found in the enclosed indoor environment. Human activity is considered the main reason causing indoor particle resuspension, which leads to human secondary exposure to PM. However, no general rules have been established to empirically relate airborne particle concentration from resuspension with specific types of human activity. This work studies the effects of electrostatic field, generated by human walking, a common human activity, on indoor particle resuspension. Particle resuspension forces, generated by human walking on indoor surface particles, can mainly be decomposed into three types: mechanical vibration, aerodynamic drag and electrostatic forces. A parametric study is carried out to compare the magnitudes of different particle resuspension force components, as well as the particle-surface adhesion force. The comparison shows that electrostatic force is a significant particle resuspension force, while the theoretically calculated particle adhesion force is much larger than each of the resuspension force components. This work suggests that real particle adhesion force is much smaller than the theoretically calculated values due to imperfect contact and thus the resuspension forces, introduced by human activity, can overcome the adhesion force to resuspend particles into the air. To testify this idea, experiments are designed to measure the real adhesion force between different particles and flooring materials with the electrostatic detachment method. This work uses particle resuspension chamber as the major facility to systematically study the walking-induced electrostatic effects on particle resuspension. Experiments are designed to measure the floor surface electrostatic field strength that can be generated by human walking in indoor environment. The measured field strength profile is used for the electrostatic field simulation in the resuspension chamber experiments. The validity of the chamber experiments is testified by comparing the resuspension coefficients concluded from the resuspension chamber experiments with the results reported from field experiments. The results of chamber experiments show that the electrostatic fields introduced by human walking can have a significant influence on indoor particle resuspension. The electrostatic effects are strongly related with such factors as particle type, flooring type, relative humidity and field polarity. Besides, this work also studies the applicability of multizone airflow and contaminant dispersion model in simulating particle resuspension and dispersion in indoor environment with a heating, ventilation and air-conditioning (HVAC) system.