Investigation of the fluid dynamic of the modified Hartmann tube equipment by high-speed video processing

Hartmann tube equipment is used in the dust explosion experimental test to screen the flammability of powdered materials (according to ISO 80079-20) and to determine the Minimum ignition energy of dust (UNI EN 13824:2004). For the test, the nominal concentration, as the ratio between the dust sample mass and the chamber test volume (1.2 liters), is considered, assuming a uniform concentration distribution. Even though adopted as standard procedure, this approach does not consider the dust cloud's non-stationary conditions inside the tube: The effect of turbulence decrease and dust sedimentation during the test duration will affect the dust concentration locally and globally within the test enclosure. Moreover, it is well known that the turbulence intensity influences Minimum Ignition Energy. This work derives from previous investigation on describing the dust cloud behavior within dust explosibility laboratory apparatuses. High-speed video recordings have recently been adopted to support the dust cloud dynamic analysis and visualize the cloud dispersion within a standard test setup, as the 20 L sphere and the modified Hartmann tube. This work intends to use different high-speed videos of dust dispersions in the modified Hartmann tube, with different injection pressure and sample mass, to focus on the behavior of the cloud at the typical delay time of the MIE measurement, i.e., 60-180 ms. Each video is processed frame by frame to reveal information on the cloud dynamics, otherwise hidden. The dust dynamic is accounted for calculating the variation in time of the brightness of pixels. This way, it is possible to obtain a set of data that incorporate the effects of the dust cloud distribution and the velocity of the particles clusters. The experimental data processing will help to focus on the time-scale and the length scale of the turbulence. The next study will focus on evaluating the time and space scale of the dust cloud and identifying the effect of ignition time delay on the MIE measurement to provide indications to operate at the most conservative conditions (higher concentration) and to avoid issues and under/overestimates due to agglomeration, sedimentation or segregation of dust particles

Sequestration of Martian CO2 by mineral carbonation

Carbonation is the water-mediated replacement of silicate minerals, such as olivine, by carbonate, and is commonplace in the Earth’s crust. This reaction can remove significant quantities of CO2 from the atmosphere and store it over geological timescales. Here we present the first direct evidence for CO2 sequestration and storage on Mars by mineral carbonation. Electron beam imaging and analysis show that olivine and a plagioclase feldspar-rich mesostasis in the Lafayette meteorite have been replaced by carbonate. The susceptibility of olivine to replacement was enhanced by the presence of smectite veins along which CO2-rich fluids gained access to grain interiors. Lafayette was partially carbonated during the Amazonian, when liquid water was available intermittently and atmospheric CO2 concentrations were close to their present-day values. Earlier in Mars’ history, when the planet had a much thicker atmosphere and an active hydrosphere, carbonation is likely to have been an effective mechanism for sequestration of CO2

Dust/vapour explosions: Hybrid behaviours?

This article underlines the peculiar behaviour of hybrid mixtures towards explosions. It should notably be noticed that there are more than additive effects on explosions severity, especially on the maximum rate of pressure rise. Moreover, the evolution of the maximum explosion pressure as a function of combustibles concentrations shows that the impact of hybrid mixtures is perceptible even for vapour amounts or dust concentrations lower than the explosion limits of the pure compounds

Application of Stereolithography to Chemical Engineering

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Etude de paramètres liés à l'inflammabilité et à l'explosivité d'échantillons de poussières de bois humide

Après avoir rappelé le mécanisme des explosions de poussière ainsi que les définitions de quelques caractéristiques des atmosphères poussiéreuses, cette brochure présente les résultats expérimentaux portant sur les caractéristiques d'explosivité obtenues avec trois poussières de bois humides (sapin, épicéa et peuplier), prélevées dans des entreprises industrielles et transmises par les services prévention des Caisses Régionales d'Assurance Maladie (CRAM

A model and a numerical scheme to compute laminar flames in dust suspensions

International audienceWe address in this paper a system of balance equations which models the low Mach number one-dimensional reactive flow generated by the combustion of a dust suspension. This model features rather general diffusion terms, with, in particular, mass diffusion coefficients which depend on the local composition and differ in function of the considered chemical species. For the solution of this system, we develop a fractional step finite volume algorithm which preserves by construction the stability properties of the continuous problem, namely the positivity of the chemical species mass fractions, the fact that they sum is equal to one, and the non-decrease of the temperature, provided that the chemical reaction is exothermic

Nanopowders explosion: Influence of the dispersion characteristics

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