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Building Simulation 2012, 5(1): 51-60 https://doi.org/10.1007/s12273-012-0068-5
Research Article | Issue | Published: 14 March 2012

Numerical study of the lock-up phenomenon of human exhaled droplets under a displacement ventilated room

Show Author's Information Naiping Gao1( ),  Qibin He2,  Jianlei Niu3
Institute of Refrigeration and Thermal Engineering, School of Mechanical Engineering, Tongji University, 1239# Siping Road, Shanghai, China
Shenzhen Institute of Building Research, 29#, three Road, Meiao, Shangmeilin, Shenzhen, China
Department of Building Services Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
Keywords:
thermal plume, displacement ventilation, human exhaled droplets, trap phenomenon, Lagrangian simulation
Cite this article:
Gao N, He Q, Niu J. Numerical study of the lock-up phenomenon of human exhaled droplets under a displacement ventilated room. Building Simulation, 2012, 5(1): 51-60. https://doi.org/10.1007/s12273-012-0068-5
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Abstract Full text About this article

This paper adopts an Eulerian-Lagrangian approach to investigate the lock-up phenomenon (or trap phenomenon) of human exhaled droplets in a typical office room under displacement ventilation (DV). A particle-source-in-cell (PSI-C) scheme is used to correlate the concentration with the Lagrangian particle trajectories in computational cells. Respiratory droplets with sizes of 0.8 μm, 5 μm and 16 μm are released from a numerical thermal manikin (NTM). The influence factors including indoor temperature gradient, heat source configuration and exhalation modes are studied. It is found that large temperature gradient would result in trap phenomenon of small exhaled droplets (smaller than 5 μm). The intensive heat source near the NTM could help to transport the small droplets to the upper zone and decrease the concentration level in the trapped zone. Both nose-exhaled and mouth-exhaled small droplets would be trapped at the breathing height when temperature gradient is sufficiently high. However, the trap height of the droplets from mouth is a little bit higher. Because of large gravitational force, it is difficult for the thermal plume to carry 16 µm respiratory droplets to the upper zone.


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About this article

Numerical study of the lock-up phenomenon of human exhaled droplets under a displacement ventilated room

Show Author's information Naiping Gao1( ), Qibin He2, Jianlei Niu3
Institute of Refrigeration and Thermal Engineering, School of Mechanical Engineering, Tongji University, 1239# Siping Road, Shanghai, China
Shenzhen Institute of Building Research, 29#, three Road, Meiao, Shangmeilin, Shenzhen, China
Department of Building Services Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China

Abstract

This paper adopts an Eulerian-Lagrangian approach to investigate the lock-up phenomenon (or trap phenomenon) of human exhaled droplets in a typical office room under displacement ventilation (DV). A particle-source-in-cell (PSI-C) scheme is used to correlate the concentration with the Lagrangian particle trajectories in computational cells. Respiratory droplets with sizes of 0.8 μm, 5 μm and 16 μm are released from a numerical thermal manikin (NTM). The influence factors including indoor temperature gradient, heat source configuration and exhalation modes are studied. It is found that large temperature gradient would result in trap phenomenon of small exhaled droplets (smaller than 5 μm). The intensive heat source near the NTM could help to transport the small droplets to the upper zone and decrease the concentration level in the trapped zone. Both nose-exhaled and mouth-exhaled small droplets would be trapped at the breathing height when temperature gradient is sufficiently high. However, the trap height of the droplets from mouth is a little bit higher. Because of large gravitational force, it is difficult for the thermal plume to carry 16 µm respiratory droplets to the upper zone.

Keywords: thermal plume, displacement ventilation, human exhaled droplets, trap phenomenon, Lagrangian simulation

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Publication history
Copyright
Acknowledgements

Publication history

Received: 12 December 2011
Revised: 15 January 2012
Accepted: 02 February 2012
Published: 14 March 2012
Issue date: March 2012

Copyright

© Tsinghua University Press and Springer-Verlag Berlin Heidelberg 2012

Acknowledgements

This study was financially supported by the National Natural Science Foundation of China under the project No. 50808133, the Research Grant Committee, Hong Kong, China, under the project No. RGC GRF 526508, and the Fundamental Research Funds for the Central Universities.

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