Quantification of preferential concentration of colliding particles in a homogeneous isotropic turbulent flow

Ernst, Martin; Sommerfeld, Martin; Laı́n, Santiago

doi:10.1016/j.ijmultiphaseflow.2019.05.007

“…This is simply due to the fact that the volume of the puff continues to increase and this continuously dilutes the aerosol concentration. Most importantly, the results of the simple model presented in (31) and (32) are in excellent agreement with those obtained from Monte-Carlo simulation. The increasing size of the contaminated cloud with time can be predicted with (38) and the centroid is given by the scaling law (16).…”

Section: Sample Model Estimation Of Airborne Transmissionsupporting

confidence: 73%

“…where φ(d, t) is the droplet nuclei concentration at the breathing zone given in (31) or (32). It is seen that the concentration of inhaled droplets larger than 10 microns significantly decreases when the mask is used.…”

Section: Respiratory Face Masksmentioning

confidence: 99%

“…The increasing size of the contaminated cloud with time can be predicted with (38) and the centroid is given by the scaling law (16). Figure 14: Droplet/aerosol concentration evolution as predicted by the analytical model presented in (31) and (32). Left frame shows the evolution starting from the log-normal distribution.…”

Section: Sample Model Estimation Of Airborne Transmissionmentioning

confidence: 99%

See 1 more Smart Citation

Host-to-Host Airborne Transmission As a Multiphase Flow Problem For Science-Based Social Distance Guidelines

Balachandar

¹

,

Zaleski

²

,

Soldati

³

et al. 2020

Preprint

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COVID-19 pandemic has strikingly demonstrated how important it is to develop fundamental knowledge related to generation, transport and inhalation of pathogen-laden droplets and their subsequent possible fate as airborne particles, or aerosols, in the context of human to human transmission. It is also increasingly clear that airborne transmission is an important contributor to rapid spreading of the disease. In this paper, we discuss the processes of droplet generation by exhalation, their potential transformation into airborne particles by evaporation, transport over long distances by the exhaled puff and by ambient air turbulence, and final inhalation by the receiving host as interconnected multiphase flow processes. A simple model for the time evolution of droplet/aerosol concentration is presented based on a theoretical analysis of the relevant physical processes. The modeling framework along with detailed experiments and simulations can be used to study a wide variety of scenarios involving breathing, talking, coughing and sneezing and in a number of environmental conditions, as humid or dry atmosphere, confined or open environment. Although a number of questions remain open on the physics of evaporation and coupling with persistence of the virus, it is clear that with a more reliable understanding of the underlying flow physics of virus transmission one can set the foundation for an improved methodology in designing case-specific social distancing and infection control guidelines.

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“…In the model, we set the minimum diameter that all drops can achieve equal to 1 μm (shown by the single point indicated in the figure) so to emphasize this effect of the model. Recall that intermittency of turbulence with the puff can create clusters of droplets and concentration of vapor and thereby significantly alter the evaporation rate ( Ernst, Sommerfeld, Lan, 2019 , Villermaux, Moutte, Amielh, Meunier, 2017 , Eaton, Fessler, 1994 ). Hence, our estimate of evaporation time is a lower bound, as governed by the d 2 -law (21) .…”

Section: Discussion On Current Assumptions and Sample Analysismentioning

confidence: 99%

“…Because of this ever decreasing evaporation rate, it may take longer for a droplet to decrease from its ejection diameter of d e to its final droplet nuclei diameter of d dr , than what is predicted by (21) . It should be noted that intermittency of turbulence and heterogeneity of vapor concentration and droplet distribution within the puff will influence the evaporation rate ( Ernst, Sommerfeld, Lan, 2019 , Villermaux, Moutte, Amielh, Meunier, 2017 , Eaton, Fessler, 1994 ). Nevertheless, for simplicity, and for the purposes of the present first order mathematical framework, we use the d 2 -law given in (21) , but with a smaller value of effective k ′ to account for the effect of non-volatiles and turbulence intermittency.…”

Section: Transport Stagementioning

confidence: 99%

Host-to-host airborne transmission as a multiphase flow problem for science-based social distance guidelines

Balachandar

¹

,

Zaleski

²

,

Soldati

³

et al. 2020

International Journal of Multiphase Flow

View full text Add to dashboard Cite

COVID-19 pandemic has strikingly demonstrated how important it is to develop fundamental knowledge related to generation, transport and inhalation of pathogen-laden droplets and their subsequent possible fate as airborne particles, or aerosols, in the context of human to human transmission. It is also increasingly clear that airborne transmission is an important contributor to rapid spreading of the disease. In this paper, we discuss the processes of droplet generation by exhalation, their potential transformation into airborne particles by evaporation, transport over long distances by the exhaled puff and by ambient air turbulence, and final inhalation by the receiving host as interconnected multiphase flow processes. A simple model for the time evolution of droplet/aerosol concentration is presented based on a theoretical analysis of the relevant physical processes. The modeling framework along with detailed experiments and simulations can be used to study a wide variety of scenarios involving breathing, talking, coughing and sneezing and in a number of environmental conditions, as humid or dry atmosphere, confined or open environment. Although a number of questions remain open on the physics of evaporation and coupling with persistence of the virus, it is clear that with a more reliable understanding of the underlying flow physics of virus transmission one can set the foundation for an improved methodology in designing case-specific social distancing and infection control guidelines.

show abstract

Data set generation at novel test-rig for validation of numerical models for modeling granular flows

Widuch

¹

,

Myöhänen

²

,

Nikku

³

et al. 2021

International Journal of Multiphase Flow

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Quantification of preferential concentration of colliding particles in a homogeneous isotropic turbulent flow

Cited by 10 publications

References 65 publications

Host-to-Host Airborne Transmission As a Multiphase Flow Problem For Science-Based Social Distance Guidelines

Host-to-Host Airborne Transmission As a Multiphase Flow Problem For Science-Based Social Distance Guidelines

Host-to-host airborne transmission as a multiphase flow problem for science-based social distance guidelines

Data set generation at novel test-rig for validation of numerical models for modeling granular flows

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