Multi-stage linear slot virtual impactor for concentration of bioaerosols
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Two linear slot virtual impactor arrangements were developed and investigated in this study. Both arrangements encompassed two-stage impaction for concentration of bioaerosols. The first arrangement consisted of eight linear slot impactors in parallel for the first stage with the designed dimensions of 87 mm (3.4Â) for the throat length, 0.305 mm (.012Â) for the accelerator throat width, and 0.457 mm (.018Â) for the receiver throat width. The second stage contained a single unit with the designed dimensions of 71 mm (2.8Â) for the throat length, 0.36 mm (0.014Â) for the accelerator throat width, and 0.49mm (0.019Â) for the receiver throat width. The second arrangement contained a single impactor for the first stage with a designed throat length of 87 mm (3.4Â), a designed accelerator throat width of 0.43 mm (.017Â), and a designed receiver throat width of 0.63mm (.025Â). The second stage also contained a single impactor with a designed throat length of 8.73 mm (3.4Â), a designed accelerator throat width of .43 mm (.017), and a designed receiver throat width of 0.63 mm (0.25Â). To verify the tolerances of the machined impactors, optical measurements were made. Both arrangements were subjected to liquid and solid particle tests and have a theoretical concentration factor of 100X. The arrangements were tested at flow rates that ranged from 10 L/min to 1000 L/min, where the collection efficiency of the minor flow was determined. An unknown acoustical phenomenon was present during aerosol tests at elevated flow rates causing low minor flow collection efficiencies. In order to test the impactors at elevated flow rates, the acoustical generation phenomenon was systematically studied and suppressed. The cutpoint for the first arrangement was 1.3Âµm AD, and the cutpoint for the second arrangement was 1.0 Âµm AD. The average Stk50 for both arrangements was 0.71. The throat velocity through the impactors ranged from 21.8 m/s to 73 m/s, and the peak efficiency for these specific throat velocities ranged from 99% to 74%, respectively.
Conerly, Shawn Charles (2003). Multi-stage linear slot virtual impactor for concentration of bioaerosols. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from