Hanhui Jin

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

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. Copyright 2013 American Association for Aerosol Research

Modeling and Numerical Analysis of the Solid Particle Erosion in Curved Ducts

This paper presents a modeling and computational study on particle erosion in curved ducts. It is found that the average erosion rates per impact range from to u2009mm3/g under current conditions. For each doubled inlet velocity, the increases of erosion rates per impact are 2–14 times. The erosion rate per impact varies with particle diameter with “√” shape through bends, which is similar to the particle deposition behavior in duct flows. The erosion rate curves per injected particle show the shapes of a 90-degree anticlockwise rotated “S” and a wide open “V,” respectively, for three larger and smaller inlet velocities. The average erosion rates per injected particle are 1.4–18.9 times those rates per impact due to huge amounts of impacting, especially for those depositing particles. It is obvious that the erosion rate distribution per impact is similar to a “fingerprint” with five clear stripes and a lower “cloud” along the bend deflection angle for the three largest particles; yet, for other smaller particles, the erosion rate distributions are much like an entire “cloud.”

A Method of Tracing Particles in Irregular Unstructured Grid System

Particle localization is commonly encountered in many areas of numerical computations. A method of tracing particles in irregular unstructured grid system is presented. The method introduced an additional set of indexical grid system to overlap the original irregular unstructured computational grid system. The particle tracing was first conducted in the indexical grid system to obtain which indexical grid cell the particle lies in, and then was carried out among the original irregular computation grid cells which were included in this localized indexical grid cell. The new method is easy to realize in numerical calculations and can apparently improve the efficiency of particle localization.