The mixing of airborne contaminants by the repeated passage of people along a corridor

Abstract

Abstract

Effects of ventilation on the indoor spread of COVID-19

“…Enhanced longitudinal dispersion by the repeated movement along a corridor has also recently been reported (Mingotti et al. 2020).…”

“…Experiments on a cylinder passing through an air curtain in a doorway, show that the air curtain is strongly disrupted by the passage and a large volume is transported through the doorway (Jha, Frank & Linden 2020a;Jha et al 2020b). Enhanced longitudinal dispersion by the repeated movement along a corridor has also recently been reported (Mingotti et al 2020).…”

The ventilation of buildings and other mitigating measures for COVID-19: a focus on wintertime

“…Although aerosols greater than about 10 μ m might, in some settings, settle from the space relatively rapidly and so they may be dispersed by people movement, smaller aerosols (e.g. less than 5 μ m) which can remain airborne for several tens of minutes may be much more strongly affected by such dispersal [70]. This dispersal may in fact dominate other dispersal processes if there is a sufficient frequency of people passing through a space.…”

“…People have widths typically in the range 0.3–0.5 m, and move at speeds of 1–2 m s −1 even when walking, and this leads to a highly turbulent wake with Reynolds number of about 10 5 . The mixing associated with this wake in corridors, supermarket aisles, meeting rooms, school classrooms or other spaces with relatively high people density and movement (even with 2 m spacing) may be key for quantifying the aerosol dispersion prior to it being ventilated or settling out from the space [70]. Indeed, with ventilation timescales of 10–20 min in typical buildings, with 5–10 air changes per hour, and the settling time of small aerosols (less than 10 μ m) being of comparable duration, the aerosols may be mixed by the wakes of many people.…”

“…To model the movement of people, cylinders of radius 0.015–0.050 m were moved back and forth along the channel, with speeds of 0.1–0.2 m s −1 , thereby providing a dynamically similar flow regime for the full-scale flow of people’s wakes. Data show that the motion of the cylinder leads to an effective dispersion coefficient for the along-channel mixing, which provides the basis for a theoretical model [70]. In experiments with a background ventilation along the corridor, in addition to the people-driven mixing, a dilution wave migrates along the corridor after the release of infected aerosol along the corridor, but the dispersion associated with people movement causes the aerosol to mix back upstream into the dilution wave, delaying the effectiveness of the ventilation.…”