Numerical simulation of airflow and particle distributions with floor circular swirl diffuser for underfloor air distribution system in an office environment.

In the present study, an underfloor air distribution (UFAD) system with a circular swirl diffuser was simulated in an office room using a three-dimensional model when thermal sources were present in the room. An Eulerian-Lagrangian model was used to predict the characteristics of air and particle phases. In the Lagrangian particle model, the effects of drag, lift, Brownian, and thermophoresis forces were considered. The results showed that the circular swirl diffuser has better airflow and thermal conditions compared with the circular direct diffusers. It was also shown that the studied UFAD system provides good thermal comfort condition. The local and mean normalized particle concentrations in different heights of the room were found reasonable, and the particle removal efficiency was between 55 and 65% for all the particle sizes. The results also showed that the large particles due to their large weight stayed in lower heights of the room and deposited on the floor. The particle concentration in the breathing zone of manikins was also investigated, and it showed that though the manikins seated close to inlet registers have appropriate thermal comfort, they encounter the highest particle concentration in their breathing zone.