Journal
BUILDING SIMULATION
Volume 5, Issue 1, Pages 51-60Publisher
TSINGHUA UNIV PRESS
DOI: 10.1007/s12273-012-0068-5
Keywords
displacement ventilation; human exhaled droplets; thermal plume; trap phenomenon; Lagrangian simulation
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Funding
- National Natural Science Foundation of China [50808133]
- Research Grant Committee, Hong Kong, China [RGC GRF 526508]
- Fundamental Research Funds for the Central Universities
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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 mu m, 5 mu m and 16 mu m 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 mu m). 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 mu m respiratory droplets to the upper zone.
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