Aerosol Deposition in Sampling Probes

Fran, B J; Wong, F.S.; McFarland, Andrew R.; Anand, N. K.

doi:10.1080/02786829208959579

Cited by 8 publications

(5 citation statements)

References 11 publications

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“…Model A has higher Stokes number, indicating higher inertial effect, with higher divergence in the nozzle that increases the likelihood for wall losses. The higher Stokes number and greater expansion ratio from shrouded nozzle inlet to nozzle exit result in lower transmission and aspiration ratios in Model A (Fran et al 1992).…”

Section: Discussionmentioning

confidence: 99%

Performance of two shrouded probes for the collection of liquid aerosols in a wind tunnel optimized for high air speeds

Fearing

Kalbasi

Zuniga

et al. 2020

Aerosol Science and Technology

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A combination of type A (high flow model) or B (low flow model) shrouded probe and appropriate isokinetic air-sampler (IAS) was tested in a wind tunnel that was optimized for high air speed testing using computational flow modeling. Liquid uranine aerosols (LUA) with AED (aerodynamic equivalent diameter) of 10 lm were generated at a constant flow rate using a vibrating orifice aerosol generator. The monodispersed aerosols were introduced into a wind tunnel at speeds of 5, 10, 15 and 20 m/s. The high flow (A) or low flow (B) model shrouded probe and the appropriate isokinetic air-sampler (IAS) was co-located to collect the LUA simultaneously during each treatment. After the test, the LUA deposited on the filters and inside the walls of the two air-samplers were collected and analyzed for fluorescence intensity units to determine the wall loss, transmission and aspiration ratios. While the type B shrouded probe had 20% (at 10 m/s) and 14.3% (at 15 m/s) higher wall loss ratios than model A, it had 16.1% (at 10 m/s) and 11.6% (at 15 m/s) higher transmission ratios compared to model A. Similarly, probe B had 17.6% (at 10 m/s) and 14.6% (at 15 m/s) higher aspiration ratios than probe A at similar air velocities. Overall, the wall loss, transmission and aspiration ratios of 10 mm AED ULA measured with two types of shrouded probes at 5, 10, 15 and 20 m/s air velocities in the optimized wind tunnel had good agreement with the range of standard data.

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Section: Discussionmentioning

confidence: 99%

Performance of two shrouded probes for the collection of liquid aerosols in a wind tunnel optimized for high air speeds

Fearing

Kalbasi

Zuniga

et al. 2020

Aerosol Science and Technology

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“…In the correlation for wall loss ratio for the inner probe of a shrouded probe, turbulent inertial deposition is taken into account by a Stokes number based upon the probe inlet diameter and the probe inlet velocity. If sedimentation is of importance in wall losses, the effect is taken into account by a particle Froude number (13). In addition to these phenomena, deposition at the inlet region is also affected by streamline bending caused by anisokineticity of sampling operation.…”

Section: Combining Eqs 1-5 Givesmentioning

confidence: 99%

“…Form of the Correlation Function for Wall Loss Ratio. Following the wall loss model of Fan et al (13), the wall loss ratio (WL) was modeled as where and and L is a non-dimensional length normalized with respect to the diameter of the inner probe. Fan et al had a Reynolds number effect embodied in their equation; however, our shrouded probe data did not show a dependency of wall losses on Reynolds number, so that parameter is not included in eq 20.…”

Section: The Correlation Function Can Then Be Represented Bymentioning

confidence: 99%

A Predictive Model for Aerosol Transmission through a Shrouded Probe

Gong

Chandra

McFarland

et al. 1996

Environ. Sci. Technol.

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Shrouded aerosol sampling probes utilize an aerodynamic decelerator (shroud) placed about an inner probe. A model has been developed for predicting the transmission ratio (T) of aerosol from a free stream to the exit plane of the inner probe. This expression, T ) FA s A pr (1 -WL), is based on use of an existing empirical model to characterize the aspiration ratios of the shroud (A s ) and inner probe (A pr ) and based upon new models to characterize the wall loss ratio in the inner probe (WL) and to relate the concentration in the core region of the shroud to the mean concentration predicted by the existing aspiration model through a correlation function, F. Extensive computational results provide a data base for specification of the correlation function. The need for the correlation function results from the phenomenon that particle enrichment in a subisokinetic shroud is non-uniform, with the concentration higher near the wall than in the center region. However, the concentration in the core region of the shroud, which is the aerosol that is ultimately sampled, is quite uniform, albeit at a level that is somewhat higher than the concentration in the free stream. This correlation function depends on particle Stokes number and the velocity ratio between free stream and shroud inlet. The predictive equation was verified by comparing its results with data from physical experiments conducted in aerosol wind tunnels with several sizes of shrouded probes. The standard error of experimental data of aerosol transmission about the predictive equation was 7.7%. The model was also evaluated in-depth by examining its ability to predict the overall aspiration of aerosol from the free stream to the inlet plane of the inner probe, wall loss ratio, and transmission of aerosols from the free stream to the exit plane of the inner probe. The results show that the model underestimates the aspiration by approximately 2%. The model for wall loss ratio underpredicts the experimental values by 8% (which influences the transmission ratio by about 2%), and transmission ratio prediction is within 1% of average experimental data. Applications of shrouded probes involve sampling air from turbulent flows, and the model is based on conditions that simulate those encountered by shrouded probes in typical stack flows. The model takes into account turbulent, inertial, and gravitational effects. It is assumed that the shrouded probe is oriented parallel to the direction of flow and the inner probe is sufficiently small such that it only samples from the core region of the shroud.

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“…This method is limited to laboratory investigations of particles smaller than 30 m, is di cult to adapt to large ducts, and requires many tests to fully characterize deposition. Other schemes allow ÿeld portability and rapid analysis by extracting particles directly from a duct (Leith, Raynor, Boundy, & Cooper, 1996); however, di culties in aspiration and transport restrict use of these techniques to particles smaller than about 10 m (Fan, Wong, McFarland, & Anand, 1992;Gong, Anand, & McFarland, 1993;McFarland, Wong, Anand, & Ortiz, 1991).…”

Section: Introductionmentioning

confidence: 99%