Thermal effect of human body on cough droplets evaporation and dispersion in an enclosed space

Abstract

A B S T R A C TThis study numerically investigated the thermal effect of human body on the time-dependent dispersion of cough droplets with evaporation process. The thermal flow of human body was imitated using a 3D thermal manikin with real body features, while a recent developed multi-component Eulerian-Lagrangian approach was used to address the effects of inhomogeneous temperature and humidity fields on droplet evaporation. By comparing the results yielded without and with the human body heat, the outcomes demonstrated strong impact of human body heat on the droplets mass fraction and local air velocity distributions. Inspirable droplets could potentially drop into respirable droplets by evaporation, although the evaporation rate was not significantly affected by body heat. The thermal effect of human body revealed its vital impacts on the time-dependent droplets dispersion. Due to the buoyancy driven thermal flow, both the vertical velocity and displacement of small droplets (≤20 μm) were completely reversed from descending to ascending, while the deposition time of large droplets (≥50 μm) were significantly delayed. With the reduced droplet size by evaporation and droplets lifted into breathing zone by human thermal effect, the inhalability and infection risks of cough droplets would be much higher in real occupied indoor spaces.

Airborne or Droplet Precautions for Health Workers Treating Coronavirus Disease 2019?

“…They report that as the relative humidity increases the extent of droplet spread decreases [18,20], yet the horizontal range of the cloud propelling the drops was found to increase with increase in relative humidity, due to the role of buoyancy of the exhaled cloud [17]. For droplets less than 20 µm in diameter, local airflow field due to body heat is an important factor in determining the extent of spread since it can lift the droplets upwards into the breathing zone [40]. Studies have also shown that depending on the flow direction and airflow pattern, increasing ventilation rate can effectively reduce the risk of long range airborne transmission [41].…”

Personal protective equipment and possible routes of airborne spread during the COVID‐19 pandemic

“…Nicas et al is cited as evidence that 99.9% of the fluid volume ejected during a cough is in large particles [3]. We believe that this should be interpreted with caution because there is also evidence suggesting that a much higher proportion of particles emitted are in the small, potentially airborne, range [2].…”

“…There remains considerable debate about the extent to which airborne spread of SARS-CoV-2 occurs. Small droplets (< 5 lm) are thought to remain suspended in the air and could theoretically be inhaled into the lungs causing infection [2]. Loose fitting 'surgical' masks will not prevent such inhalation and only a tight-fitting filtering mask is adequate.…”

“…Loose fitting 'surgical' masks will not prevent such inhalation and only a tight-fitting filtering mask is adequate. Conversely larger (> 5 lm) particles do not remain suspended in the air [2] and can only cause infection if they are immediately inhaled, or after contact with a surface they land on.…”

Characterisation and analysis of indoor tornado for contaminant removal and emergency ventilation

“…human, carpet, electronic devices, etc.) [4][5][6]. When contaminants are highly concentrated locally, these commonly used ventilation systems would be most likely promoting the transport of local contaminants rather than removing or isolating them away from further spreading.…”