Development and laboratory characterization of a prototype coarse particle concentrator for inhalation toxicological studies

This paper presents the development and laboratory characterization of a prototype slit nozzle virtual impactor that can be used to concentrate coarse particles. A variety of physical design and flow parameters were evaluated including different acceleration and collection slit nozzles and Reynolds numbers (Re). Performance parameters investigated include concentration factor (CF), cutpoint, collection efficiency, minor-to-total flow ratio, and particle losses. Investigation of the effect of the different parameters on the overall performance of the virtual impactor made it possible to optimize its design. For a flow rate of 11.4 LPM/cm length of the acceleration slit, Re of 2520, and a 5% minor-to-total-flow ratio (r), the corresponding size cut-off (d50) was 2.4 μm. Under these conditions the CF is approximately 17 and remains constant for particles larger than 3 μm. Also for these conditions the pressure drop in both the minor and major flows were <13 Pa (0.05 in water) and 448 Pa (1.8 in water), respectively, and average particle losses were <10%. Finally, separation and concentration of the coarse particles occurred without any significant distortion of their size distribution making this system suitable for inhalation toxicological studies.