Dusan Licina

Human convective boundary layer and its interaction with room ventilation flow

This study investigates the interaction between the human convective boundary layer (CBL) and uniform airflow with different velocity and from different directions. Human body is resembled by a thermal manikin with complex body shape and surface temperature distribution as the skin temperature of an average person. Particle image velocimetry (PIV) and pseudocolor visualization (PCV) are applied to identify the flow around the manikins body. The findings show that the direction and magnitude of the surrounding airflows considerably influence the airflow distribution around the human body. Downward flow with velocity of 0.175xa0m/s does not influence the convective flow in the breathing zone, while flow at 0.30xa0m/s collides with the CBL at the nose level reducing the peak velocity from 0.185 to 0.10xa0m/s. Transverse horizontal flow disturbs the CBL at the breathing zone even at 0.175xa0m/s. A sitting manikin exposed to airflow from below with velocity of 0.30 and 0.425xa0m/s assisting the CBL reduces the peak velocity in the breathing zone and changes the flow pattern around the body, compared to the assisting flow of 0.175xa0m/s or quiescent conditions. In this case, the airflow interaction is strongly affected by the presence of the chair.

Effectiveness of a personalized ventilation system in reducing personal exposure against directly released simulated cough droplets

UNLABELLEDnThe inhalation intake fraction was used as an indicator to compare effects of desktop personalized ventilation and mixing ventilation on personal exposure to directly released simulated cough droplets. A cough machine was used to simulate cough release from the front, back, and side of a thermal manikin at distances between 1 and 4 m. Cough droplet concentration was measured with an aerosol spectrometer in the breathing zone of a thermal manikin. Particle image velocimetry was used to characterize the velocity field in the breathing zone. Desktop personalized ventilation substantially reduced the inhalation intake fraction compared to mixing ventilation for all investigated distances and orientations of the cough release. The results point out that the orientation between the cough source and the breathing zone of the exposed occupant is an important factor that substantially influences exposure. Exposure to cough droplets was reduced with increasing distance between cough source and exposed occupant.nnnPRACTICAL IMPLICATIONSnThe results from this study show that an advanced air distribution system such as personalized ventilation reduces exposure to cough-released droplets better than commonly applied overhead mixing ventilation. This work can inform HVAC engineers about different aspects of air distribution systems’ performance and can serve as an aid in making critical design decisions.