Monte Carlo N-particle tracking of ultrafine particle flow in bent microtubes

<p>The problem of large pressure-differential-driven laminar convective–diffusive ultrafine aerosol flow through bent microtubes is of interest in several contemporary research areas including; release of contents from pressurized containment vessels, aerosol sampling equipment, advanced scientific instruments, gas-phase microheat exchangers, and microfluidic devices. In each of these areas, the predominant problem is the determination of the fraction of particles entering the microtube that is deposited within the tube and the fraction that is transmitted through. Due to the extensive parameter restrictions of this class of problems, a Lagrangian particle tracking method making use of the coupling of the analytical stream line solutions of Dean for convective motion and a sampling of a Gaussian distribution for diffusive motion is a useful tool in problem characterization. This method is a direct analog to the Monte Carlo N-Particle method of particle transport extensively used in nuclear physics and engineering. In this work, 10-nm-diameter particles with a density of 1 g/cm³ are tracked within microtubes with toroidal bends with pressure differentials ranging between 0.2175 and 0.87 atmospheres. The tubes have radii of 25 microns or 50 microns and the radius of curvature is either 1 m or 0.3183 cm. The carrier gas is helium, and temperatures of 298 K and 558 K are considered. Numerical convergence is considered as a function of time step size and of the number of particles per simulation. Particle transmission rates and deposition patterns within the bent microtubes are calculated.</p> <p>Copyright © 2016 American Association for Aerosol Research</p

Use of Nitrogen Trifluoride To Purify Molten Salt Reactor Coolant and Heat Transfer Fluoride Salts

The molten-salt-cooled nuclear reactor is one of the Generation IV reactor types. One of the challenges of implementing this reactor is purifying and maintaining the purity of the various molten fluoride salts that will be used as coolants. The method used for Oak Ridge National Laboratory’s molten salt experimental test reactor was to treat the coolant with a mixture of H₂ and HF at 600 °C. In this Article, we evaluate thermal NF₃ treatment for purifying molten fluoride salt coolant candidates based on nitrogen trifluoride’s (1) past use to purify fluoride salts; (2) other industrial uses; (3) commercial availability; (4) operational, chemical, and health hazards; (5) environmental effects and environmental risk management methods; (6) corrosive properties; (7) thermodynamic potential to eliminate impurities that could arise due to exposure to water and oxygen. Our evaluation indicates that nitrogen trifluoride is a viable and safer alternative to the previous method