Abstract
The human cough is a significant vector in the transmission of respiratory diseases in indoor environments. The cough flow is characterized as a two-stage jet; specifically, the starting jet (when the cough starts and flow is released) and interrupted jet (after the source supply is terminated). During the starting-jet stage, the flow rate is a function of time; three temporal profiles of the exit velocity (pulsation, sinusoidal and real-cough) were investigated in this study, and our results showed that the cough flow’s maximum penetration distance was in the range of a 50.6–85.5 opening diameter (D) under our experimental conditions. The real-cough and sinusoidal cases exhibited greater penetration ability than the pulsation cases under the same characteristic Reynolds number (Rec) and normalized cough expired volume (Q/AD, with Q as the cough expired volume and A as the opening area). However, the effects of Rec and Q/AD on the maximum penetration distances proved to be more significant; larger values of Rec and Q/AD reflected cough flows with greater penetration distances. A protocol was developed to scale the particle experiments between the prototype in air, and the model in water. The water tank experiments revealed that although medium and large particles deposit readily, their maximum spread distance is similar to that of small particles. Moreover, the leading vortex plays an important role in enhancing particle transport.
Highlights
The human cough is known to be a significant vector for transmitting respiratory diseases in indoor environments
Our objective was to perform an experimental study of the two-stage cough jet and investigate the effects that different boundary conditions such as temporal exit velocity profiles, cough duration and velocity scale have on cough flow penetration
Bourouiba et al [37] and Sangras et al [28] emphasized the puff or interrupted-jet stage, but this study shows that the starting-jet stage is quite important, to the extent that its consideration is necessary to understand cough dynamics and associated pathogen spread
Summary
The human cough is known to be a significant vector for transmitting respiratory diseases in indoor environments. Droplets evaporate and become droplet nuclei [1] These droplets and droplet nuclei can contain elements such as sodium, potassium and chloride in solutes; DNA, lipids, glycoproteins and proteins in suspended insoluble solids; and, infectious pathogens if released by an infectious patient. Exposure to these pathogencontaining droplets can occur via both short- (within 1–2 m of the source patient) and long(beyond about 2 m in the indoor environment) range routes. Short-range airborne exposure via smaller droplets or droplet nuclei is important in close proximity infection
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