Abstract
Airborne transmission of respiratory pathogens in indoor environments remains a significant global health challenge. While existing research broadly addresses ventilation effectiveness, there is a critical need to understand how specific diffuser placements influence early-phase aerosol dispersion immediately following a cough event. This study uses Computational Fluid Dynamics (CFD) with an Eulerian-Lagrangian approach and the Discrete Phase Model to analyze initial droplet transport, evaporation, and nuclei concentration under different air distribution configurations. The results demonstrate that conventional parallel exhaust configurations, though effective at reducing overall particle mass, can fail to control the lateral spread of infectious nuclei in the short term. In contrast, placing exhaust diffusers above the cough source reduces the lateral particle spread by approximately 40% compared to conventional layouts. Additionally, maintaining the WHO-recommended two-meter distance results in an 82-89% reduction in particle number concentration during the early dispersion phase. These findings underscore the importance of diffuser placement for controlling short-term particle dispersion immediately after a cough event in mechanically ventilated office environments. The study's scope is limited to early-phase dispersion dynamics within a 10-second simulation period, and further research is needed to assess long-term aerosol suspension, removal mechanisms, and infection risk. Nonetheless, the results offer practical insights for HVAC design and support the integration of ventilation strategies with physical distancing measures to reduce near-field exposure risks.