The effect of relative air humidity on the evaporation timescales of a human sneeze

Abstract

The present paper investigates droplet and aerosol emission from the human respiratory function by numerical and experimental methods, which is analyzed at the worst-case scenario, a violent sneeze without a face covering. The research findings develop the understanding of airborne disease transmission relevant to COVID-19, its recent variants, and other airborne pathogens. A human sneeze is studied using a multiphase Computational Fluid Dynamics (CFD) model using detached eddy simulation coupled to the emission of droplets that break up, evaporate, and disperse. The model provides one of the first experimental benchmarks of CFD predictions of a human sneeze event. The experiments optically capture aerosols and droplets and are processed to provide spatiotemporal data to validate the CFD model. Under the context of large random uncertainty, the studies indicate the reasonable correlation of CFD prediction with experimental measurements using velocity profiles and exposure levels, indicating that the model captures the salient details relevant to pathogen dispersion. Second, the CFD model was extended to study the effect of relative humidity with respect to the Wells curve, providing additional insight into the complexities of evaporation and sedimentation characteristics in the context of turbulent and elevated humidity conditions associated with the sneeze. The CFD results indicated correlation with the Wells curve with additional insight into features, leading to non-conservative aspects associated with increased suspension time. These factors are found to be associated with the combination of evaporation and fluid-structure-induced suspension. This effect is studied for various ambient air humidity levels and peaks for lower humidity levels, indicating that the Wells curve may need a buffer in dry climates. Specifically, we find that the increased risk in dry climates may be up to 50% higher than would be predicted using the underlying assumptions in Wells’ model.

RETRACTED: Influence of indoor relative humidity on the number concentration, size distribution, and trajectory of sneeze droplets: Effects on social distancing guidelines

“…(6) and vapor transport Eq. (7) included the energy source term S e,evap, and vapor concentration source term S Y,evap from droplet evaporation ( Fontes et al, 2020 ; Stiehl et al, 2022 ). Therefore, they included the influences of droplets' evaporation on changing the local humidity and temperature.…”

“…Understanding the dynamic behavior of respiratory droplets under different indoor conditions can suggest prevention guidelines to reduce COVID-19 spread ( Wang et al, 2021 ). Previous studies introduced various techniques for measuring the respiratory droplet velocity profiles, including particle image velocimetry (PIV) and laser Doppler anemometry ( Bahl et al, 2020 ; Stiehl et al, 2022 ), and airflow visualization methods such as shadowgraph imaging (Tang et al, 2013). However, due to the limitations of experiments in determining short-range/direct transmission of respiratory droplets, computational fluid dynamics (CFD) modeling was also used in the literature ( Vuorinen et al, 2020 ).…”

Statistical analysis of infectious disease transmission risk based on exhaled respiratory droplet trajectory distribution

“…In Ref. 6, instead, the role of ambient relative humidity on the evaporation of droplet from a sneeze is analyzed. The effectiveness of face masks in absorbing the larger droplets and limiting the diffusion of smaller droplets is assessed numerically in Refs.…”

A computational fluid dynamics—Population balance equation approach for evaporating cough droplets transport

“…Meanwhile, the exhaled microorganisms could also travel 2 m and remain suspended in the air within a room. Stiehl et al (2022) used the particle imaging velocimetry (PIV) to studies the evolution of aerosols and droplets expelled during a human sneeze. They extracted the sneeze emission concentration at 0.6 m and 0.9 m away from the mouth and found that maximal concentration is found in region slightly lower than the mouth at 0.6 m. These studies shed light on the droplets and aerosols transmission and reveal the influencing factors.…”