Development of a Low-cost Aerosol Concentrator for Bioaerosol Sampling
Francisco Romay, RYNE JUIDICI, Aaron Collins, David Y. H. Pui, University of Minnesota
Abstract Number: 106
Working Group: Instrumentation and Methods
Abstract
Bioaerosols are typically present at low concentrations in the environment, making them difficult to measure at small sampling flow rates. A practical solution to this problem is to use an aerosol concentrator that increases the concentration of the particles of interest, (>1 μm).
Historically virtual impactors have relied on CNC machining due to the tight dimensional tolerances, which has resulted in high manufacturing costs, but also in design limitations due to the machining process. The reduced cost and increased availability of high-resolution stereolithography (SLA) printing, has enabled us to greatly innovate the design and manufacturing of virtual impactors. The new design for additive manufacturing enabled both the accelerating nozzle and receiving tube to be printed in a single unit at that about 1/10th of the cost of traditional machining, while still maintaining an adequate nozzle size and geometry for a sharp cutoff curve. Our design has a nominal 400:1 concentration factor, with an inlet flow rate of 120 L/min and an outlet concentrated flow rate of 0.30 L/min, with two virtual impactor stages in series operating at the same diameter cutpoint. The first stage has 20 sets of nozzles in an opposing jet configuration, leading to a second stage with a single nozzle and receiving tube. The aerosol concentrator was evaluated experimentally with highly monodisperse oleic acid particles generated by a flow-focusing monodisperse aerosol generator, followed by a multiplet reduction impactor. The experimental aerodynamic diameter cutpoint was 1.84μm with a geometric standard deviation of 1.16, which is considered a sharp separation cutoff curve. The total pressure drop of the new aerosol concentrator was 3.9 kPa at the nominal inlet flow rate. This small flow resistance allowed us to select a miniature high-speed 35W blower. The new aerosol concentrator will be used with a low-cost, induced-fluorescent bioaerosol sensor.