Studies of bioaerosols dispersion and deposition

Brief:

The increasing incidence of airborne transmitted diseases in an indoor environment has prompted the attention of studying expiratory droplet dispersion, transportation and deposition in built environments.

We have considered a case that a source (i.e. a patient who generate droplets) and a receiver (i.e. the susceptible object other than the source) presented in a mechanical ventilated room. Ten micrometer droplet nuclei, with different emission velocities, are selected to represent large expiratory droplets which still can be inhaled to respiratory tracts. The droplet dispersion and mixing magnitude under well-mixed and displacement ventilation schemes are evaluated numerically. The receiver’s exposure to droplet nuclei is analyzed under two orientations relative to the source. Numerical results show that the droplet dispersion and mixing under displacement ventilation is consistently poorer than those under the well-mixed scenarios. Very low concentration regions are observed under displacement ventilation. The intake dose is reduced substantially for both ventilation schemes when the source emits droplets at the face-to wall orientation, compared to that at the face-to-face case.

We developed an experimental facility designed and built with the objective of understanding the deposition of bioaerosols in indoor environments. Multiple depositions of two microorganisms Staphylococcus and Micrococcus inside a test chamber were investigated under two air mixing conditions. Airflow rate was demonstrated to have an influence on the concentration homogeneity. An increased proportion of particle deposition was found in the floor section near the chamber wall opposite to the air inlet when air mixing was not enhanced by the mixing fans. Both the experimental results and Eulerian-Lagrangian computations revealed that a small mixing fan inside the chamber prompted very effective mixing while non-homogeneity was observed even at a very high ventilation rate. The results showed that both ventilation rate and mixing conditions in the ventilated chamber have influence on the bioaerosol dispersion and deposition.

Further information:

Mui KW, Wong LT, Wu CL, Lai ACK, 2009. Numerical modeling of exhaled droplet nuclei dispersion and mixing in indoor environments, Journal of Hazardous Materials 167(1-3) 736-744.

Wong LT, Chan WY, Mui KW, Lai ACK, 2010. An experimental and numerical study on deposition of bioaerosols in a scaled chamber, Aerosols Science and Technology 44(2)117-128.