Experimental Study of Solid Particle Deposition in 90° Ventilated Bends of Rectangular Cross Section with Turbulent Flow

Abstract

Nowadays, ventilation ducts, especially duct bends, play a significant role in filtering aerosol contaminant for the built environment. This article experimentally investigates practical averaged aerosol deposition in 90 • ventilated bends of rectangular cross section by measuring particle concentration changes at bend inlet and outlet in steady state. The measured penetrations at Reynolds number Re = 17,900 and 35,600 are in good agreement with previously published data at small Stokes number, which justifies the effectiveness of the measurement process. Particle penetration decreases from approximately 100% for St = 5.2 × 10 −4 particles to 64% for St = 0.55 particles in acrylic glass bends. For the particles of Stokes number larger than 0.089, particle penetration is much higher than that in previous studies. This behavior is believed to be caused by the consideration of particle rebounce from bend wall in the presence of centrifugal force. The changes in Reynolds number do not significantly alter the trend of deposition velocity and penetration. Deposition velocities are compared and verified with available droplet data and current numerical and analytical analysis. For the high deposition velocity increase compared to that in straight ducts, the major mechanism is attributed to the flow impaction onto outer bend wall. In this type of bend, secondary flows and streamwise eddies provide a further reason for distinct deposition increase of small particles. In a word, the deposition mechanisms are analyzed analytically and systematically, and then classified in order clearly. In addition, two empirical models were proposed in this article, which are valid for Stokes number St = 5.2 × 10 −4 -0.55 under the experimental conditions.

Effects of rib spacing and height on particle deposition in ribbed duct air flows

“…In general, the accurate measurement of particle behavior and deposition in complex turbulent air flows are quite challenging for experiments, while it could be numerically predicted with suitable CFD models [12,13]. For aerosol particle flows, the Eulerian-Lagrangian methods have been proved as effective and credible models to predict particle deposition in turbulent flow by many researches [14e18].…”

Experimental Views of Tran-Bend Particle Deposition in Turbulent Flow with Nanoscale Effect

“…e fluctuating velocities of particle flow were found to be higher than those of airflow at the inlet of the bend. Tables 1 and 2 [10,[14][15][16][17][18][19][20][21][22][23][24]. e scarcity of experimental work during earlier years might be attributed to the reason that both the particle deposition and distribution are comprehensive and can be varied by many factors even in straight pipe/channel/ducts [25][26][27][28].…”

“…e aerosol deposition in the bend was found to be larger than that in straight ducts with fully developed turbulent flows. Sun et al designed laboratory experiments to test the particle flow through bends made of different materials in the ventilation system [22,23]. ey discovered particle concentration distribution, deposition, and penetration phenomena and developed models on deposition velocity and penetration.…”

“…Wilson et al [21] Ghaffarpasand et al [24] Sun et al [22,23] Lin et al [ turbulent induced enhancement effects. Sippola and Nazaroff experimentally investigated two typical combined bends under various ventilation system conditions [19,20].…”

Distribution and penetration efficiency of nanoparticles between 8–550nm in pipe bends under laminar and turbulent flow conditions

“…Liu and Li [10] simulated the deposition characteristic of particles at different air velocities for d p = 1-30 lm, and showed that an increase in curvature of the pipe induces a reduction of the particle penetration. Sun et al [11,12] investigated the particle concentration distribution and deposition in three-dimensional 90 degrees bends experimentally, and demonstrated the effects of inlet mass concentration, Reynolds number and wall material on the particle concentration distribution and deposition.…”