Journal of Health and Safety at Work

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Introduction: Usually, in the toxicological studies of airborne particulate pollutants, inhalation exposure chambers are used for providing and distributing the test atmosphere uniformly and stability in the respiratory zone of laboratory animals. The purpose of this study was to design, evaluate and optimize a whole-body exposure chamber, specifically for small laboratory animals exposed to particulate matter.
Material and Methods: In the first, the papers and scientific resources which had provided the technical details and performance of the inhalation exposure chambers were studied, and the advantages, disadvantages and those factors affecting their performance were extracted. Then the assumptions of the initial design of the chamber were prepared with regard to the principles of fluid dynamics and the standard conditions of lab animal housing. To create a uniform distribution of particles inside the chamber, guide plates of flow were used in the upper cone. Numerical simulation and ANSYS Fluent software were used to optimize the initial design. Drawing geometry of the chambers was done using Design modeler software and meshing of the computational field using ANSYS meshing software. The particles used had a mean aerodynamic diameter of 10 μm, spherical, inert, and a density of 1,400 kg. m^-3 and entered the chamber at the carrier gas velocity. Particle concentration was measured in the chambers along the cylindrical radius at 10 cm intervals on the x-axis. Then the percentage of variation coefficient of the particle concentration for each line was calculated. In the final analysis of the results, the geometry design with the lowest coefficient of variation of particle concentration along the selected sampling line was selected as the best chamber design.
Results: The optimized inhalation chamber has a dynamical flow and consists of a cylinder with two upper and lower cones. The flow enters from the upper cone and after passes through the guide plates, distributes in the interior of the chamber and exits from the lower cone. The k-ε turbulence and Discrete Phase Models could have modeled this problem. Design No. 7 was optimal design with the lowest coefficient of variation of the concentration (4.08%).
Conclusion: The numerical simulation method for planning and optimizing of the chambers, at a much lower cost than the empirical methods, was able to provide comprehensive information on the solution field. The analysis of this information led to the selection of the best chamber design to provide uniform concentration of the particles in the respiratory region of the animals.

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Introduction: Polymer nanofiber filters have great potential for controlling particulate pollution due to their high filtration efficiency and low pressure drop. This study aimed to fabricate nanofiber membranes from a biodegradable polymer through solution electrospinning to address both health and environmental concerns, along with analyzing their morphological characteristics. The filtration performance of the prepared membranes was evaluated against different particle sizes under two air face velocities. 
Material and Methods: The nanofiber membranes were fabricated from aqueous poly(vinyl alcohol) (PVA) solutions at various concentrations from 5 to 6 w/v%  under different process parameters. The morphological characteristics of the nanofibers were examined using field-emission scanning electron microscopy (FE-SEM), while structural properties such as basis weight and thickness were measured to estimate porosity. Filtration performance, including efficiency and pressure drop, was evaluated at two standard air face velocities (2.5 and 5.3 cm/s) using a media test system. In addition, the quality factor of the prepared membranes was calculated.
Results: The electrospun nanofibers were uniform and bead-free, with the mean fiber diameters ranging from 106 to 151 nm. The filtration efficiencies were 95.72–99.92 % for sub-micron particles (0.3 and 0.5 µm), and 99.43–100 % for larger particles (1 and 3 µm). The pressure drop ranged from 67 to150 Pa at an air face velocity of 2.5 cm/s, and from 58 to150 Pa at an air face velocity of 5.3 cm/s.
Conclusion: The 6 wt.% PVA nanofiber membrane electrospun at 15 kV, 0.5 mL/h, and 15 cm produced thinner fibers (approximately 106 nm) and exhibited higher efficiency for 0.3 µm particles (99.89 % and 99.92 % at 2.5 and 5.3 cm/s air face velocities, respectively). For this membrane with thinner fibers, the pressure drop increased from 67 to 150 Pa with rising the air face velocity.