Su W.C., Vincent J.H. New experimental studies to directly measure aspiration efficiencies of aerosol samplers in calm air

Journal of Aerosol Science, 2002, Volume 33, Issue 1, P. 103-118.Typical air movements in many indoor living and working places are as low as, or less than, 0.1 m/s, and so conditions might best be described in terms of calm, as opposed to moving air—or perhaps some combination of the two. However, the historyof aerosol sampling science has been dominated by studies of the aspiration efficiencies of sampling devices in moving air, and there have been veryfew definitive studies of calm air sampling, even for verysimple sampling systems. With this in mind, this paper sets out the basis for the development of a larger bodyof experimental work, and describes an experimental method bywhich unambiguous measurements maybe made for a range of simple aerosol sampling systems (i.e., shape and orientation). The method, referred to as the “direct method”, owes much to the ‘thread-of-droplets’ approach proposed byLipatov et al. (J. Aerosol Sci.17 (1986) 763) for studies of aspiration e!ciencyin moving air. In the new method, monodisperse large droplets of olive oil with aerodynamic diameter in the range from 40 to 70 mkm, were generated using a vibrating ori4ce aerosol generator and the experimental conditions were controlled verycarefullyso that a well-de4ned, vertically-falling droplet stream was obtained. By the application of appropriate tracking apparatus, visual observation of this droplet stream was used to map the pattern of particle trajectories near a given sampling inlet and to identifylimiting particle trajectories in order to calculate aspiration e!ciency. In an initial application of the new method, measurements of aspiration efficiencywere carried out for upwards-facing thin-walled sampling tubes, and the results were found to be in satisfying agreement with the numerical results of Agarwal and Liu (1980, in the Am. Ind. Hyg. Assoc. J.41 (1980) 191) and the numerical and experimental results of Yoshida et al. (Kagaku Kogaku Ronbunshu4 (1978) 123). The results of this initial studyprovide confidence that the method described maynow be applied to a wider range of sampling systems.