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

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 μm 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. Copyright © 2018 American Association for Aerosol Research

本实验于冲击器（impactor）中开展，该装置的喷嘴与冲击板间距极小，远小于单喷嘴直径。本研究针对粒径范围为3~15 μm的气溶胶，探究了该冲击器内的气溶胶沉积形貌。实验观察到环形沉积形貌，其内径与环宽随粒子粒径发生变化。具体而言，环的内径及宽度与斯托克斯数（Stokes number，Stk）存在关联：环直径随斯托克斯数增大而减小，环宽则随其增大而增加。当斯托克斯数约为0.4时，环形结构闭合，最终形成近似均匀的圆盘状沉积形貌。此类环形沉积形貌与此前文献中报道的形貌均不相符，数量级分析表明该沉积过程以惯性效应为主导。版权所有© 2018 美国气溶胶研究协会（American Association for Aerosol Research）