Gas Collection Efficiency and Entrance Flow Effect of an Annular Diffusion Denuder

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Abstract
In air sampling, an annular diffusion denuder (ADD) is often used to trap specific gases from an air sample stream. In a dimensional analysis, the gas collection efficiency was shown to be dependent on two parameters: the Peclet number and the annulus radii ratio. Also, the entrance flow effect on the gas collection efficiency was examined. In determining the gas collection efficiency of an ADD, the gas concentration and flow field were solved numerically from their governing equations using a computational fluid dynamics technique. The collection efficiency of gas diffusing to the annulus wall was then calculated from the gas concentration and velocity profiles. After validating the methodology, a parametric calculation of the gas collection efficiency was made, and a mathematical model based on the calculation was developed.