Particle deposition in ventilation duct with convex or concave wall cavity

A numerical study is carried out on particle deposition in ducts with either convex or concave wall cavity. Results show that, if compared with smooth duct, particle deposition velocities (V-d(+)) increase greatly in ducts with wall cavities. More specifically, for tau(+)<1, V-d(+) increase by about 2-4 orders of magnitude in the cases with the convex and concave wall cavities; for tau(+)>1, V-d(+) grows relatively slower. Enhancement of particle deposition with wall cavities is caused by the following mechanisms, i.e., interception by the wall cavities, expanded deposition area, and the enhanced flow turbulence. In general, addition of wall cavities is contributive for particle deposition, so it provides an efficient approach to remove particles, especially with small size, e.g., PM2.5. Moreover, the convex wall cavity leads to a larger increment of V-d(+) than the concave wall cavity. However, taking pressure loss into account, though V-d(+) is relatively lower, duct with the concave wall cavity is more efficient than that with the convex wall cavity.