Solid Particle Collection Characteristics on Impaction Surfaces of Different Designs

Abstract

The effect of solid particle loading on the collection efficiency of a single-stage impactor with different impaction surface designs has been investigated. Experimental results show that the time-varying collection efficiency depends on the surface coating condition, thickness of particle deposit, and impaction surface design. Deposited particles change the surface condition such that the particle collection efficiency decreases with time for the coated impaction surface while it increases with time for the uncoated impaction surface. However, after heavy loading, the collection efficiency eventually approaches nearly the same asymptotic value whether the impaction surface is coated or not. The impaction surface with an inverted conical cavity and an orifice plate alleviates particle bounce and reentrainment problems during particle collection process, resulting in .a much greater collection efficiency than the conventional design, which uses flat impaction surface.

Reducing Particle Bounce and Loading Effect for a Multi-Hole Impactor

“…The designation of the open cavity in this study was not similar to earlier investigations (Scott and Ranz 1976;Biswas and Flagan 1988;Tsai and Cheng 1995;Chang et al 1999). The dimensions of the open cavity were based on ease of use and were different from those used elsewhere (Figure 1), facilitating assembly of the flat-ring aluminum plate and filling the TSA.…”

“…However, impaction cavities and wells can improve impactor performance compared to flat surfaces. Several studies have examined varying configuration and sampling conditions for impactors with collection cavities such as quiescence, no surface coating and additional substrates (Scott and Ranz 1976;Biswas and Flagan 1988;Tsai and Cheng 1995;Chang et al 1999). Their experimental results indicate that greased substrates eliminate particle bounce.…”

“…To determine accurate particle size distributions, particles impacting on the collection substrate must stick to it without bouncing off resulting in subsequent collection on a downstream stage (Dzubay et al 1976;Esmen 1980;Markowski 1984;Lai et al 2002). Particle bounce-off depends on many factors such as the impaction surface characteristics, coating type and depth, particle types, particle loading on the impaction surface, sampling conditions and impaction substrate design (Rao and Whitby 1978a, b;Reischl and John 1978;Turner and Hering 1987;Newton et al 1990;Pak et al 1992;Tsai and Cheng 1995;Chang et al 1999;Hinds 1999). Therefore, in order to obtain unbiased particle size and mass concentration distributions, particle bounce-off and re-entrainment from the impaction surface must be minimized.…”

Evaluation of Particle Bounce in Various Collection Substrates to be Used as Vaporizer in Aerosol Mass Spectrometer

“…The particle number concentration before entering the impactor was maintained at higher than »500 particles/cm 3 to obtain reliable counting statistics. To prevent heavy particle loading on the surface of the collection surface (as the surface becomes loaded with particles, the incoming particles will strike on previously deposited particles) (Tsai and Cheng 1995), the particle bounce measurement was completed within 10 min. The frequent thermal desorption of the sample in the AMS would prevent particles from being heavily loaded on substrate.…”

Design and Testing of the NCTU Micro-Orifice Cascade Impactor (NMCI) for the Measurement of Nanoparticle Size Distributions

“…For uncoated substrates used as a collection surface to avoid interference with chemical analysis from coating materials, conditioning the relative humidity of the incoming aerosols of the MOUDI was suggested to ensure that the measurement of mass distributions is not influenced by particle bounce (Vasiliou et al 1999;Chen et al 2011). To increase the particle loading capacity on impaction substrates, many efforts have been made using oil-soaked Teflon filters (Turner and Hering 1987;Tsai et al 2012), rotating substrates Tsai et al 2012), and specially designed impaction plates (Tsai and Cheng 1995).…”