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

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.

Moringa oleifera Lam. leaf powder antioxidant activity and cytotoxicity in human primary fibroblasts.

Moringa oleifera Lam. (MO) leaf powder has been well studied, however, understanding how extraction methods of antioxidant compounds affect human primary fibroblasts still needs to be determined. The antioxidant capacity was analyzed through a copper reduction capacity method and primary human skin fibroblasts were evaluated for cytotoxicity using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Antioxidant activity under the influence of methanolic solvents (Trolox equivalents of 160.18 nmol/µL) was 17 times higher than under aqueous solvents. Interestingly, the aqueous extract showed less toxicity in comparison to the methanolic, as cells resulted more susceptible to concentrations ranging from 0.05 to 5 mg/L. Although, MO methanol solvent showed a higher antioxidant capacity in comparison to the aqueous solvent, it presented greater cytotoxicity. Thus, it is concluded that the aqueous extract could be suitable for downstream processing and applications.

Design and computational fluid dynamics investigation of a personal, high flow inhalable sampler.

The objective of this research was to develop an inlet to meet the inhalable sampling criterion at 10 l min(-1) flow using the standard, 37-mm cassette. We designed a porous head for this cassette and evaluated its performance using computational fluid dynamics (CFD) modeling. Particle aspiration efficiency was simulated in a wind tunnel environment at 0.4 m s(-1) freestream velocity for a facing-the-wind orientation, with sampler oriented at both 0 degrees (horizontal) and 30 degrees down angles. The porous high-flow sampler oriented 30 degrees downward showed reasonable agreement with published mannequin wind tunnel studies and humanoid CFD investigations for solid particle aspiration into the mouth, whereas the horizontal orientation resulted in oversampling. Liquid particles were under-aspirated in all cases, however, with 41-84% lower aspiration efficiencies relative to solid particles. A sampler with a single central 15-mm pore at 10 l min(-1) was also investigated and was found to match the porous sampler's aspiration efficiency for solid particles; the single-pore sampler is expected to be more suitable for liquid particle use.