Effects of indoor air stability on exhaled contaminant flow and thermal plume in the interpersonal breathing microenvironment

Indoor air stability is a general term that refers to the indoor air's tendency to encourage or discourage its initial inertia motion. In stable conditions where vertical temperature gradients are positive, would prevent the vertical motion of fluid flows, thus the initial inertia motions are maintained, whereas in unstable conditions where vertical temperature gradients are negative, fluids experience intensive convection, thus the initial inertia motions are more easily to get disturbed. This study experimentally and numerically investigated the dispersion of exhaled contaminants and body thermal plume in a displacement-ventilated room integrated with unstable and stable conditions. Two real-human subjects participated in the full-scale experiments. The effects of participants' relative position with reference to the ventilation vents and of ventilation rates on the flow field were examined. Results show that the thermal stratification associated with the displacement ventilation system was disturbed by unstable conditions, resulting in a uniformly distributed contaminants and thermal fields, therefore a reduced exposure level; whereas the thermal stratification was enhanced by stable conditions so that the transport of contaminants and thermal more inclined to follow their initially released direction and led to a relatively high exposure level in the breathing microenvironment. Air distribution in unstable conditions, when compared with stable conditions, was more sensitive to the relative position between the participants and the vents. Increasing the ventilation rate could greatly reduce the contaminant level of unstable conditions but may not achieve as good results in stable conditions. This paper has practical significance in controlling the transmission of exhaled contaminants and preventing the spread of infectious diseases.

Automated summary

This study investigated the dispersion of exhaled contaminants and body thermal plume in a displacement-ventilated room integrated with stable and unstable conditions. Results show that stable conditions reduce exposure levels while unstable conditions increase exposure risks.