Expiratory Aerosol Transport in a Scaled Chamber under a Variety of Emission Characteristics: An Experimental Study

Pollutant concentration is a major factor affecting exposure. Expiratory process generates high-velocity droplets for a very short period of time that leads to highly transient temporal and nonuniform concentration profiles. In this work, solid aerosol generated by an expiratory process was measured spatially and temporally inside a scaled ventilated chamber. Conventional ceiling-supply, ceiling-return, and displacement ventilation systems were studied. Two sizes of monodisperse microspheres, 0.05 and 10 μm, were generated by a modeled expiratory process. Two heated, scaled manikins were used to mimic a simple yet typical exposure scenario with an aerosol source and a receiver while buoyancy flow was presented. First, the influence of relative orientation of the source to the inlet diffuser on spatial concentration was investigated. The source was located in such a position that the bulk airflow was against to the expiratory process. Second, the relative orientation of the source-to-receiver was also investigated to study how the concentration distribution was being affected. Two orientations were tested as one of the source faced to the receiver and the other source faced to a sidewall. The dimensionless temporal concentration results were presented at six locations. Transient ventilation effectiveness was also evaluated and compared for both ventilation systems. With the "counter flow" scenario, the emitted particles tended to suspend in the mechanical ventilated chamber for a long period; this indicates a high exposure will be resulted. For the displacement scheme of the "face-to-wall" orientation, due to the low y-component of air velocity, poor lateral dispersion was observed.