Numerical Prediction of the Performance of a Shrouded Probe Sampling in Turbulent Flow

The U.S. Environmental Protection Agency (EPA), the Florida Department of Environmental Protection (FLDEP), and Texas A&M University collaborated in the design, construction, and testing of a unique, highly crosslinked, Teflon-coated inlet and manifold gas and aerosol sampling system that is being used in EPA aircraft atmospheric pollution characterization studies. The aircraftborne ambient sampling system, which consists of a Teflon-coated shrouded probe coupled to a Teflon-coated aluminum manifold, is designed to collect reactive gases (e.g., mercury and halide species) and aerosols for subsequent analysis and characterization. The shrouded inlet probe was tested for particle transmission ratios in a high-speed aerosol wind tunnel. An existing wind tunnel was upgraded from a maximum wind speed of 13.4 m/s (48 km/h or 30 miles/h) to 50.5 m/s (182 km/h or 113 miles/h) to test this probe. The wind tunnel was evaluated for compliance with the criteria of ANSI 13.1 to establish the acceptability of its use in testing probes. The results demonstrated that the velocity and tracer gas concentration profiles were within the specified limits. A wellcharacterized ThermoAndersen Shrouded Probe (Model RF-2-112) was also tested to check tunnel performance and test methodology. These findings suggest that shrouded probes can be used for low speed (∼100 miles/h) aircraft applications. The transmission ratio of these probes is a significant improvement over the conventional aircraft-mounted, sharp-edged isokinetic diffuser-type inlets.

Section: Use Of Shrouded Probes As Sampling Inletsmentioning

confidence: 99%

Section: Use Of Shrouded Probes As Sampling Inletsmentioning

confidence: 99%

Wind Tunnel Evaluation of an Aircraft-Borne Sampling System

Irshad

McFarland

Landis

et al. 2004

“…One is the determination of entry efficiency of sampling probe and the improvement of the sampling inlet to reduce the sampling error during anisokinetic sampling (Chung and Ogden 1986). The other is "shrouded probe" (Gong et al 1993;Chandra and McFarland 1997;Twohy 1998;Irshad et al 2004). In the shrouded probe, the shroud automatically adjusts the free stream air velocity to the inner sampling probe air velocity.…”

Section: Introductionmentioning

confidence: 99%

Development of Variable Flow Rate Isokinetic Sampling System for 0.5–15-μm Aerodynamic Diameter Particles

Ichitsubo

Ōtani

2012

Isokinetic sampling is required when evaluating the aerodynamic sizes of particles released from dry powder inhalers (DPI) under simulated breathing condition since anisokinetic sampling may lead to significant sampling error for coarse particles. We propose an isokinetic measuring system for aerosol particles from a stream in a narrow conduit of variable flow rates (variable flow rate aerosol sampler, VFAS) combined with Aerodynamic Particle sizer R APS TM spectrometer (model 3321, TSI Inc.). The VFAS was capable of generating variable sampling flow rates by adjusting the flow resistance of makeup air to produce constant flow rate of aerosol to the APS. The penetrations through the VFAS-APS system were measured using monodisperse particles with a size range of 0.7-15 µm by applying a rectangular flow rate-time pattern of sampling air, and we found that the VFAS-APS system can measure the number concentration of particles with the particle detection efficiency (particle penetration through the system) of almost unity. The VFAS-APS system may be a powerful tool to measure the size and concentration of powder released by the DPI in the size range of 0.5-15 µm.

“…Gong et al (1993Gong et al ( , 1996 carried out numerical simulations of a shrouded probe aerosol inlet, which has flow that can be treated in a two-dimensional manner. Hu and McFarland (2007) used CFD simulation to gain valuable insight into the aerosol behavior and the location of particle deposition in a wetted wall bioaerosol sampling cyclone.…”

Section: Introductionmentioning

confidence: 99%

A Computational Fluid Dynamics Study of Particle Penetration through an Omni-Directional Aerosol Inlet

Tang

Guo

McFarland

2010

Computational fluid dynamics (CFD) was used to study aerosol penetration through the entrance section of a bell-shaped omnidirectional ambient aerosol sampling inlet. The entrance section did not include either an insect screen or a large-particle preseparator. Simulations of the flow field were carried out for wind speeds of 2, 8, and 24 km/h and a fixed exhaust flow rate of 100 L/min; and, particle tracking was performed for 2 to 20 µm aerodynamic diameter particles. Penetration calculated from CFD simulations was in excellent agreement with experimental results from previous studies with the root mean square relative error between simulation and experimental data being 3.8%. CFD results showed that the most significant regional particle deposition occurred on the upwind side of a curved flow passage between two concentric axisymmetric shells of the inlet housing and that deposition at the leading edges of the shells and within the exhaust tube was far less significant. At a wind speed of 2 km/h, penetration was affected by gravitational settling, e.g., penetration of 20 µm particles was 71.9% when gravity was included and 80.4% without gravity. At higher wind speeds gravity had little effect. An empirical equation was developed to relate aerosol penetration to a Stokes number, a gravitational settling parameter, and a velocity ratio. Good fits of the correlation curves to experimental data and numerical results were obtained.