An Empirical Model for the Aspiration Efficiencies of Blunt Aerosol Samplers Orientated at an Angle to the Oncoming Flow

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Abstract
In this paper the problem of developing a theoretical model to determine the aspiration efficiency of blunt samplers orientated with respect to the oncoming flow is investigated. It is assumed that the sampler is orientated such that its axis makes an angle θ with the flow and particles are aspirated through an orifice in its surface. This system has been investigated by Vincent, who developed a model that compared well with experimental results for θ = 0° but less favorably as θ increased. Therefore, in this paper an investigation has been made into the reasons for these discrepancies. The flow pattern near the sampler has been studied, and it is shown that certain assumptions, made by Vincent, that are true in the limiting case of θ = 0° are no longer valid when θ > 0°. In particular, the stagnation area identified for 8 = 0° no longer exists, and the turning of the fluid to face the orifice does not seem to be playing a part in the flow pattern. A new model is developed for a spherical sampler orientated with respect to the flow, and this is compared with the existing experimental work for the human head. It is found that although the model has been extended to include these features, the comparison is still not satisfactory and, therefore, a more mathematical approach might be appropriate.