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The objective of this work was to estimate the effects of different filter test housings on measurements of automotive air filter efficiency. This objective was motivated by the questions that arise from designing filters on the basis of uniform face velocities and testing filters in housings providing nonuniform velocities. Velocity distributions upstream of a filter were measured with a laser Doppler anemometer and then used with filtration models to estimate filter initial efficiency. A single filter design was tested in a standard and modified SAE J726 Universal Panel Filter Test Housing and in a housing with a shallow angle diffuser followed by a rectangular duct matched to the filter cross section. The velocity measurements showed that the SAE J726 housing presents a very non-uniform flow to the filter. Housing modifications had small effects. The diffuser-duct housing profiles approach fully-developed duct flow profiles.

Problems have been encountered in the repeatability of performance measurements in the panel filter universal test housing specified by the Society of Automotive Engineers' SAE J726 Air Cleaner Test Code. The flow fields inside the test housing were analyzed for two different sized filters using flow visualization and two component laser doppler velocimeter (LDV) measurements. The analysis clearly indicated that the flow inside the housing was very turbulent, recirculating and separated from the walls. The filter in the housing receives non-uniform velocities with the central part receiving higher velocities than the sides. Simple filtration theories were applied to calculate the local filtration efficiencies for monodisperse particles for a clean filter. The predicted local efficiencies were integrated to give the effect of the non-uniform velocities upon the overall filter efficiency.