The Effects of Bluntness and Orientation on Two-Dimensional Samplers in Calm Air

Abstract

This article uses numerical simulation to investigate the effect of sampler bluntness, particle size, and sampler orientation on aspiration efficiency in calm air. The procedure is to first numerically solve the velocity field around the sampler in calm air and then to trace the particle trajectories and calculate the the aspiration efficiency. Two samplers are studied: a two-dimensional parallel plate and a two-dimensional -blunt cylinder. The variation of aspiration efficiency with particle size shows two minima between two asymptotic values. When the samplers are facing upward, the asymptotic values are 1 for very small particles and the ratio of particle settling velocity to suction velocity for very large particles. At other orientations, the horizontal-facing and the downward-facing, the asymptotic value for large particles is 0. The sampler bluntness has an important effect in the region of particle size where there is competition between the particle inertia and the fluid drag force (i.e., 5 y m < d < 100 y m in our case). A blunt sampler always has higher aspiration efficiency than does a sharp-edged sampler in this region of particle sizes. For very small particles and very large particles, the aspiration efficiencies approach asymptotic values and the sampler bluntness has little effect. The results also show that the sampler orientation affects the predicted aspiration efficiency.

Experimental Measurements and Numerical Calculations of Aspiration Efficiency for Cylindrical Thin-Walled Aerosol Samplers in Perfectly Calm Air

“…Although some aerosol scientists have studied calm air aerosol sampling for thin-walled probes facing downwards and horizontally, their research has been based largely on numerical simulations (Kaslow and Emrich 1974;Dunnett 1992;Chung and Dunn-Rankin 1993). Before the present research there were almost no experimental data available for downwards and horizontal sampling to provide evidence for validating such numerical work.…”

Numerical Study of the RespiCon Sampler Performance in the Calm Air

“…Mathematical models for thin-walled tube sampling in still air were developed by Agarwal and Liu (1980) and Dunnett (1992). The aspiration efficiency for the twodimensional blunt sampler operating in calm air at horizontal and upward and downward vertical orientations was studied by Chung and Dunn-Rankin (1993). Mathematical model and the results of studies of the spherical sampler operating in the calm air are given by Galeev and Zaripov (2003) and Dunnett et al (2006).…”

A Numerical Study of Calm Air Sampling with a Blunt Sampler

“…For such conditions the model of calm air sampling is an accurate description of indoor aerosol sampling conditions. Past experimental and theoretical studies of the aspiration efficiency for samplers operating in calm air include Davies and Peetz (1954), Emrich (1973, 1974), Yoshida et al (1978), Belyaev and Kustov (1980), Agarwal and Liu (1980), Grinshpun et al (1989), Chung and Dunn-Rankin (1993) and Dunnett (2002). Although these earlier works have increased our understanding of how samplers perform when operating in calm air conditions, our knowledge is far from complete.…”