Performance evaluation of a recirculated personalized air curtain combined with displacement ventilation in mitigating indoor airborne transmission

To mitigate the risk of airborne transmission, we explored the integration of a recirculated personalized air curtain (rPAC) with displacement ventilation (DV) using computational fluid dynamics (CFD) simulations. The rPAC can utilize indoor air directly, drawing clean air from the lower room space supplied by the DV system. Our study assessed the effectiveness of the rPAC in reducing the intake fraction of expiratory droplets from transient coughing and steady speaking indoors. We categorized droplets into small (initial diameter ≤20 μm), medium (50 μm), and large (100 μm) sizes. Large droplets from both activities generally had negligible intake fractions. The rPAC effectively reduced the intake fraction from coughing and speaking, although its performance varied with respiratory activities and exhalation directions. At 0° and 30°, the rPAC reduced the intake fraction of small coughing droplets by over 90 % and medium droplets by 74 %-98 %, with significant reductions also observed for speaking. However, at 60°, the rPAC increased the intake fraction of medium coughing droplets and small droplets from speaking due to complex airflow-droplet interaction dynamics. This study highlights the potential of rPAC as an effective control measure to improve indoor air quality and mitigate respiratory disease transmission, though its effectiveness is influenced by exhalation direction and droplet size.