AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Examination of Sampler Efficiency of Thin-Walled Reference Samplers in Low Velocity Freestreams
KIMBERLY ANDERSON, T. Renee Anthony, University of Iowa
Abstract Number: 320 Working Group: Instrumentation and Methods
Abstract Background: Particle aspiration efficiency is calculated as the ratio of the concentration over the concentration in the freestream. This equation relies on the assumption that the reference sampler measuring the freestream concentration captures a representative sample of the aerosol in the freestream. The performance of the thin-walled reference sampler in moving air has been extensively investigated; however, the performance of these samplers in low velocities has not been studied. If the thin-walled reference sampler under-aspirates the true concentration of large particles in low velocity environments, then the calculated sampler efficiency or human aspiration efficiency will be higher than it should be at these particle sizes. If particle bounce significantly contributes to the measured reference concentration, then the resulting calculated efficiency will be lower than it should be.
Objective: The objective of this study is to (1) evaluate large particle aspiration for a thin-walled reference sampler in low freestream velocities and (2) quantify the effect of particle bounce on secondary aspiration.
Methods: CFD modeling was used to investigate aspiration efficiency of a thin-walled reference sampler for three freestream velocities: 0.1, 0.2, and 0.4 m/s, seven particle sizes: 7, 22, 52, 68, 82, 100, and 116 micro-meters, and two CoR values: 0.0 (no-bounce) and 0.9 (bounce). Fluid simulations used the standard k-epsilon turbulence model. Particle trajectories were simulated using laminar particle tracks and used to determine the upstream critical area. These areas were used to calculate sampler efficiency.
Results: Thin-walled sampler efficiency was significantly different when secondary aspiration (from particle bounce) was allowed (p=0.011). Aspiration at 0.1 m/s was significantly lower from unity at the no-bounce condition (p=0.012) and approaching significance for the bounce condition (p=0.07). Sampler efficiency was not significant different from unity at 0.2 and 0.4 m/s for either the bounce or no bounce condition.