In an external field and ion flow the most useful theory to resolve the charging process of particle is Liu-Kapadia's charging theory. However, in case of the dimensionless electric field ω, this theory requires a smaller grid size in radial direction and long CPU time to acquire correct charging characteristics. So we investigate the relation between ω and the necessary equal grid size in order to correct charging characteristics. The application of the Spline correction function to calculate the slope of concentration of ion adjacent to the surface of particle is useful. Furthermore, when ω is less than 0.5 and greater than 50.0, Liu-Kapadia's theory can be replaced by other simple theory.
This work describes the performance of the midget impinger for submicron aerosols. Collection efficiencies of the midget impinger were investigated numerically and experimentally. Flow fields in the midget impinger were solved using FLUENT, which is a computational fluid dynamics software and calculates RNG k-ε model for intermediate Re number, k-ε model for high Re number, and laminar flow model. Polystyrene latex (PSL) particles ranging from 0.10 to 3.1 μm and monodisperse diethyl-hexyl-sebacate (DEHS) mist ranging from 0.3 to 1.5 μm were aerosolized and introduced into the midget impinger. These theoretical and experimental results show a good agreement. The impinger shows poor performance for submicron particles and bubbling in the impinger contributes to 10% higher collection efficiency for submicron mist particles than that without water filling. PSL particles larger than 0.6 μm show bounce off the bottom surface of the impinger.
Dry deposition velocities of SO2 to various model surfaces were calculated from total flux of SO2 and SO42- measured on their surfaces assuming that dry deposition velocities of SO42- to various surfaces were 1/5 as large as SO2. Estimated dry deposition velocities of SO2 to water, soil, vegetation and building material surfaces ranged 0.01∼0.64 cm·s-1. The results of spatial distribution for dry deposition flux of sulfur estimated with dry deposition velocities of SO2 has indicated that the average value in 1995 was 9.4 gS·m-2·y-1. Considerably high the values over 12.5 gS·m-2·y-1 were estimated for urban, Banan and Nantong area where large amounts of SO2 had been emitted by coal combustion. In spite of the lowest dry deposition flux (4.4 gS·m-2·y-1) over Tongliang area, it was 2.2 times as high as that of Tokyo, Japan (2.0 gS·m-2·y-1). Higher dry deposition flux over eastern area than western area must be caused by the difference of weather, geographical conditions and sulfur emission. During 1986∼1995, the average dry deposition for sulfur accounted for 67% of sulfur emission in Chongqing. This result indicated that the difference between dry deposition and emission was deposited as precipitation and transported to other area.