Three-dimensional computational fluid dynamics modeling of particle uptake by an occupational air sampler using manually-scaled and adaptive grids

Abstract

This work presents fluid flow and particle trajectory simulation studies to determine the aspiration efficiency of a horizontally oriented occupational air sampler using computational fluid dynamics (CFD). Grid adaption and manual scaling of the grids were applied to two sampler prototypes based on a 37-mm cassette. The standard k–ε model was used to simulate the turbulent air flow and a second order streamline-upwind discretization scheme was used to stabilize convective terms of the Navier–Stokes equations. Successively scaled grids for each configuration were created manually and by means of grid adaption using the velocity gradient in the main flow direction. Solutions were verified to assess iterative convergence, grid independence and monotonic convergence. Particle aspiration efficiencies determined for both prototype samplers were undistinguishable, indicating that the porous filter does not play a noticeable role in particle aspiration. Results conclude that grid adaption is a powerful tool that allows to refine specific regions that require lots of detail and therefore better resolve flow detail. It was verified that adaptive grids provided a higher number of locations with monotonic convergence than the manual grids and required the least computational effort.

Evaluation of a prototype inhalable sampler

“…The Bland-Altman also reveals that while there are a few metal samples outside of the 95% confidence intervals, or two standard deviations of the mean, a majority of the samples are clustered near a mean difference of zero, meaning that the prototype and IOM concentrations actually matched each other quite well, especially when metal concentrations were lower. This adds to study evidence supporting the prototype's applicability for sampling lower concentrations Koehler & Peters, 2015;L'Orange et al, 2016;Landazuri et al, 2016;Stewart et al, 2017).…”

“…Due to the higher flow rate of this sampler at 10 L min -1 , several studies indicate that the prototype sampler yields promise for detecting lower concentrations and potentially for shortening necessary sampling durations L'Orange et al, 2016;Landazuri et al, 2016;Stewart et al, 2017). The 3-piece prototype performance closely matches the inhalable sampling criterion and is therefore deemed a simpler alternative to both the Button and IOM samplers L'Orange et al, 2016).…”

“…One unique aspect of the PHISH is that due to the inclusion of an internal capsule, this sampler eliminates the concern for particles depositing of the walls. In addition to the capsule, this study and others mention that the high flow rate makes this sampler desirable for shorter sampling durations or in low concentration sampling environments in which the analytical limit of detection needs to be met (Anthony, Cai, Mehaffy, Sleeth, & Volckens, 2017;Koehler & Peters, 2015;Landazuri, Saez, & Anthony, 2016;Stewart et al, 2017).…”