Aerosol Deposition on Electroformed Wire Screens

Abstract

Insect screens, which are usually an integral component of an air sampling inlet, can cause inadvertent deposition of larger aerosol particles. Numerical and experimental studies were performed to characterize aerosol deposition on commercially available electroformed wire screens for aerodynamic particle diameters between 3 and 20 μ m, Stokes numbers between 0.49 and 20, wire widths between 35 and 160 μ m, and screen open area fractions of 0.56 to 0.90. With increasing values of Stokes numbers, the actual collection efficiency increases gradually to a maximum value that is asymptotic to the fraction of open area. Deposition is characterized in terms of a standardized screen efficiency, which is the actual efficiency divided by the areal solidarity (1–fraction of open area). A correlation equation has been developed for the electroformed mesh screens, which relates the standardized efficiency to the fraction of open area, the Stokes number, the interception parameter, and the Reynolds number based on wire size. Data obtained from experimental studies with two screen types and numerical studies with those, plus two additional screen types, over a wide range of Stokes numbers and wire Reynolds number (Re _w ) from about 0.5 to 30, collapse to a single correlation curve, which is valid for the range of variables tested. The pressure drop across the screens is low, on the order of 1 Pa for face velocity values that are on the order of 1 m/s. A regression analysis was used to obtain coefficients that fit the results of the numerical experiments to an existing pressure loss model.

Funding was provided by the Aerosol Technology Laboratory of the Texas Engineering Experimental Station (TEES) and by the U.S. Army Research, Development and Engineering Command under Contract DAAD13-03-C-0050. We wish to thank Drs. Jerold R. Bottiger and Edward S. Stuebing, who are the technical managers of the contract. Computational time for the simulations was provided by the Texas A&M University Supercomputing Facility.