Ring-shaped deposition patterns in small nozzle-to-plate distance impactors

Abstract

Experiments were carried out in an impactor, where the distance between the impactor nozzle and the impactor plate was small, much less than one nozzle diameter in separation. The aerosol deposition patterns in this impactor were investigated for aerosols in the 3-15 mm diameter range. Ring-shaped deposition patterns were observed where the internal diameter and thickness of the rings were a function of the particle diameter. Specifically, the inner diameter and ring thickness were correlated to the Stokes number, Stk; the ring diameter decreased with Stk, and the ring thickness increased with Stk. At Stk » 0:4 the ring closed up, leaving a mostly uniform disk deposition pattern. These ring patterns do not appear to correspond to patterns previously described in the literature, and an order of magnitude analysis shows that this is an inertially dominated process.

CFD-DEM Coupling Model for Deposition Process Analysis of Ultrafine Particles in a Micro Impinging Flow Field

“…However, it changes to be a “ring” when Re = 700 for stk = 0.25 in Figure 3 b. Similarly, there are the primary ring and another ring in the previous research [ 7 , 10 ]. Halo deposit which is ring-shaped was also mentioned in the experimental results [ 8 , 11 ].…”

“…R 2 is defined as the radius of the ring deposit. stk affects the deposit patterns in Figure 9, which was demonstrated before [5][6][7]10,41]. As stk increases, the halo gets closer to the primary deposit until it vanishes, thus R 0 decreased, which agrees favorably well with the experimental result [8].…”

“…Figure 11 shows the categorization of two particle deposition patterns (i.e., “halo” and “ring”) in terms of the value of Re and stk . The solid points and hollow points were taken from present simulations and experiment results from papers [ 4 , 7 , 10 , 11 , 12 ], respectively. A “halo” rarely occurs when Re is larger than 1000.…”

“… Categorization of the “halo” and “ring” deposit in terms of the value of Re and stk . The solid points and hollow points were taken from the simulation and experiment results [ 4 , 7 , 10 , 11 , 12 ], respectively. …”

“…Several mechanisms have been proposed through analysis of experiment results to explain the formation of the “halo” deposits, such as gravitational sedimentation, the hydrodynamic effect, particle inertia, Magnus lift, Saffman lift, and particle rebound and re-entrainment in most researches [ 6 , 7 , 8 , 9 , 10 , 11 ]. The combined method of computational fluid dynamics and discrete particle method (CFD-DPM) considered a powerful and reliable technique was utilized to simulate particle movement in the impactor to achieve the location of particle deposition [ 12 ].…”