A Compact Wind Tunnel for Evaluating Aerosol Samplers

Abstract

A small wind tunnel (305 cm in length and with an inside diameter of 59 cm) was designed, fabricated, evaluated, and modified to meet flow field uniformity criteria consistent with those established by the U.S. Environmental Protection Agency for PM₁₀ sampler testing. With an arrangement of three jet pumps located near the intake of the wind tunnel, velocity profiles in the plane of the test section near the exhaust of the wind tunnel demonstrated low variability. The coefficients of variation (CVs) of the mean velocities at traverse points within the test section were < 5 percent in the velocity range of 0.6 to 1.4 m/s. Stable particle size distributions of polydisperse aerosols of ceramic beads injected along the centerline of the wind tunnel through one of the jet pumps were generated with a vibrating feed generator [type 200 Zeeospheres^®; count median aerodynamic diameter (CMAD), 1.6 to 1.8 μm; mass median aerodynamic diameter (MMAD), 5.1 μm; and geometric standard deviation (GSD), 1.7 to 1.8] and with a fluidized bed aerosol generator (type X-62 Zeeospheres; CMAD, 1.5 μm; MMAD, 11.3 to 11.4 μm; and GSD, 1.6). Stable particle count and mass concentrations were observed with the fluidized bed generator. Measurements across a vertical traverse of the test section at a wind velocity of 0.4 m/s indicated an average concentration of 46.7 counts/cm³ with a between-point CV of 3.8 percent and an average mass concentration of 1.97 mg/m³ with a between-point CV of 5.0 percent. Aerosol mass concentrations measured at the center of the airstream in the test section were temporally stable at concentrations ranging from 1.1 to 5.6 mg/m³ for periods ranging from 1 to 10 hours. The wind tunnel should be suitable for determining the particle sizing characteristics of an aerosol sampler (or the portion of the sampler installed into the wind tunnel) with a cross-sectional area of no more than about 400 cm². Eddins, P.M.; Gao, P.; Dillon, H.K.; Farthing, W.E.: A Compact Wind Tunnel for Evaluating Aerosol Samplers. Appl. Occup. Environ. Hyg. 11(1):44–55; 1996.