A CFD study of the transport and fate of airborne droplets in a ventilated office: The role of droplet−droplet interactions

doi:10.1007/s11783-021-1465-8

Front. Environ. Sci. Eng.

2022, Vol. 16

Issue (3) : 31 https://doi.org/10.1007/s11783-021-1465-8

RESEARCH ARTICLE

A CFD study of the transport and fate of airborne droplets in a ventilated office: The role of droplet−droplet interactions

Allan Gomez-Flores¹, Gukhwa Hwang², Sadia Ilyas², Hyunjung Kim^1,²(

)

¹. Department of Environment and Energy, Jeonbuk National University, Jeonju Jeonbuk 54896, Republic of Korea
². Department of Mineral Resources and Energy Engineering, Jeonbuk National University, Jeonju Jeonbuk 54896, Republic of Korea

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Abstract

• Coulomb and Lennard−Jones forces were considered for droplet interactions.

• The net droplet interactions were repulsive.

• Repulsive droplet interactions increased the transport of droplets.

• Repulsive droplet interactions significantly modified the fate of droplets.

Previous studies reported that specially designed ventilation systems provide good air quality and safe environment by removing airborne droplets that contain viruses expelled by infected people. These water droplets can be stable in the environment and remain suspended in air for prolonged periods. Encounters between droplets may occur and droplet interactions should be considered. However, the previous studies focused on other physical phenomena (air flow, drag force, evaporation) for droplet transport and neglected droplet interactions. In this work, we used computational fluid dynamics (CFD) to simulate the transport and fate of airborne droplets expelled by an asymptomatic person and considered droplet interactions. Droplet drag with turbulence for prediction of transport and fate of droplets indicated that the turbulence increased the transport of 1 μm droplets, whereas it decreased the transport of 50 μm droplets. In contrast to only considering drag and turbulence, consideration of droplet interactions tended to increase both the transport and fate. Although the length scale of the office is much larger than the droplet sizes, the droplet interactions, which occurred at the initial stages of release when droplet separation distances were shorter, had a significant effect in droplet fate by considerably manipulating the final locations on surfaces where droplets adhered. Therefore, it is proposed that when an exact prediction of transport and fate is required, especially for high droplet concentrations, the effects of droplet interactions should not be ignored.

Keywords Droplet interactions Aerosols Colloids CFD Transport Fate

Corresponding Author(s): Hyunjung Kim

Issue Date: 21 June 2021

Cite this article:

Allan Gomez-Flores,Gukhwa Hwang,Sadia Ilyas, et al. A CFD study of the transport and fate of airborne droplets in a ventilated office: The role of droplet−droplet interactions[J]. Front. Environ. Sci. Eng., 2022, 16(3): 31.

URL:

https://academic.hep.com.cn/fese/EN/10.1007/s11783-021-1465-8
https://academic.hep.com.cn/fese/EN/Y2022/V16/I3/31

Fig.1 Diagram of the office used for simulations in Case 1: turned−on ventilator, opened door, and closed window, and Case 2: turned−on ventilator, opened door, and opened window.

Fig.2 Air velocity magnitude (m/s) and arrow flux for Case 1: turned−on ventilator, opened door, and closed window, and Case 2: turned−on ventilator, opened door, and opened window. The planes crossed the central point of the office.

Fig.3 Turbulent energy dissipation (ε, m²/s³) for Case 1: turned−on ventilator, opened door, and closed window, and Case 2: turned−on ventilator, opened door, and opened window.

Fig.4 Fate of 1 μm droplets at 600 s of simulation for Case 1: turned−on ventilator, opened door, and closed window, and Case 2: turned−on ventilator, opened door, and opened window according to modeling approach: (i) drag without ε and no droplet−droplet interactions, (ii) drag with ε and no droplet−droplet interactions, (iii) drag with ε and droplet−droplet interactions. The particles were enlarged for better representation.

Tab.1 Sum of the number of droplets adhered to relevant surfaces in the office room during 600 s of simulation according to modeling approach for Case 1 (turned−on ventilator, opened door, and closed window) and Case 2 (turned−on ventilator, opened door, and opened window). 25 droplets were released at 0 and 10 s for a total of 50 droplets

Fig.5 Fate of 50 μm droplets at 600 s of simulation for Case 1: turned−on ventilator, opened door, and closed window, and Case 2: turned−on ventilator, opened door, and opened window according to modeling approach: (i) drag without ε and no droplet−droplet interactions, (ii) drag with ε and no droplet−droplet interactions, (iii) drag with ε and droplet−droplet interactions. The particles were enlarged for better representation.

Fig.6 Interaction energy profiles of 1 and 50 μm droplets as a function of separation distance between droplets.

Fig.7 Control simulation for the path and final position of 50 μm droplets at 0 and 3 mili seconds. Drag and turbulence were not considered. The particles were enlarged for better representation.

Fig.8 Control simulation for the transport and fate of 50 μm droplets at 120 s according to the modeling approach. The particles were enlarged for better representation.

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