Built Environment & Energy Laboratory
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Chen, C., Zhao, B., Cui, W., Dong, L., An, N., Ouyang, X. (2010). The effectiveness of an air cleaner in controlling droplet/aerosol particle dispersion emitted from a patient's mouth in the indoor environment of dental clinics. Journal of the Royal Society Interface, 7, 1105-1118. (Particle dispersion, Infectious particle, Hospital)

Dental health-care workers (DHCWs) are at high risk of occupational exposure to droplets and aerosol particles emitted from patients’ mouths during treatment. We evaluated the effectiveness of an air cleaner in reducing droplet and aerosol contamination by positioning the device in four different locations in an actual dental clinic. We applied computational fluid dynamics (CFD) methods to solve the governing equations of air flow, energy, and dispersion of different-sized airborne droplets/aerosol particles. In a dental clinic, we measured the supply air velocity and temperature of the ventilation system, the air flow rate and the particle removal efficiency of the air cleaner to determine the boundary conditions for the CFD simulations. Our results indicate that use of an air cleaner in a dental clinic may be an effective method for reducing DHCWs’ exposure to airborne droplets and aerosol particles. Further, we found that the probability of droplet/aerosol particle removal and the direction of airflow from the cleaner are both important control measures for droplet and aerosol contamination in a dental clinic. Thus, the distance between the air cleaner and droplet/aerosol particle source as well as the relative location of the air cleaner to both the source and DHCW are important considerations for reducing DHCWs’ exposure to droplets/aerosol particles emitted from patient’s mouth during treatments.

Chen, C., Zhao, B. (2010). Some questions on dispersion of human exhaled droplets in ventilation room: answers from numerical investigation. Indoor Air, 20, 95-111. (Particle dispersion, Infectious particle, building)

This study employs a numerical model to investigate the dispersion characteristics of human exhaled droplets in ventilation rooms. The numerical model is validated by two different experiments prior to the application for the studied cases. Some typical questions on studying dispersion of human exhaled droplets indoors are reviewed and numerical study using the normalized evaporation time and normalized gravitational sedimentation time was performed to obtain the answers. It was found that modeling the transient process from a droplet to a droplet nucleus due to evaporation can be neglected when the normalized evaporation time is less than 0.051. When the normalized gravitational sedimentation time is less than 0.005, the influence of ventilation rate could be neglected. However, the influence of ventilation pattern and initial exhaled velocity on the exhaled droplets dispersion is dominant as the air flow decides the droplets dispersion significantly. Besides, the influence of temperature and relative humidity on the dispersion of droplets can be neglected for the droplet with initial diameter less than 200μm; while droplet nuclei size plays an important role only for the droplets with initial diameter within the range of 10μm-100μm.