Assessment of threat arising by closed - volume explosions of fuel - air mixtures

The method of estimation of maximal parameters of combustion of gaseous mixtures in closed space is presented. Estimation of chemical composition of combustion products is based on simplified rules of decomposition of reactive medium. Exemplary calculations of temperature, pressure, heat of combustion of hydrocarbon/air mixtures are presented. The accuracy of presented method was validated by comparison with calculations performed by thermodynamic numerical code that include wide list of chemical substances present in combustion products. The obtained results confirm applicability of the proposed method to predict closed space combustion parameters of gaseous mixtures. Semi-empirical methods of estimation of flammability limits are briefly referred

Numerical estimation of thermal ignition conditions for reactive medium with Gaussian distribution of activation energy

The article investigates the solutions of the one-dimensional stationary integro-differential heat equation. The source of heat release is determined through the Gaussian distribution function of the activation energy. In such a statement, the critical conditions for the existence of a bounded solution depend on the distribution variance. With the help of numerical methods, such dependences are obtained; for their explanation, the analytical approximations of the thermal explosion theory are used.

Evaluation of Changes in the Permeability Characteristics of a Geotextile–Polynorbornene Liner for the Prevention of Pollutant Diffusion in Oil-Contaminated Soils

In this study, changes in the permeability characteristics of a geotextile–polynorbornene liner at different oil pollutant contact times were evaluated. Experiments and numerical analyses were performed, and ASTM D5887 and ASTM D6766 were applied as test methods. The test results show that, when the pollutant contact time and pressure head were 4 h and 75 kPa, the reaction between the geotextile–polynorbornene liner and the pollutant was almost complete. Moreover, a numerical analysis was used to measure the ratio of the concentration of the pollutant that permeated through the geotextile–polynorbornene liner to the initial pollutant concentration at different pollutant contact times. The ratio was between 70 and 83% after a pollutant contact time of 0.5 h and between 0.1 and 1.0% after 4 h. The test and numerical analysis results confirm that, as a reactive medium, the geotextile–polynorbornene liner can effectively prevent the diffusion of oil pollutants by changing its permeability characteristics.

Scavenging of radionuclides in multicomponent medium with first-order reaction kinetics: Lagrangian and Eulerian modeling

<p>A process of the removal of dissolved elements in the ocean by adsorption onto sinking particulate matters (scavenging) is studied analytically and using Lagrangian and Eulerian numerical methods. The generalized model of scavenging in a multicomponent reactive medium with first-order kinetics consisting of water and multi-fraction suspended particular matter has developed. Two novel numerical schemes were used to solve advection-diffusion-reaction equations for advection-dominated flows. The particle tracking algorithm based on the method of moments was developed. It is free on time step limitation necessary for an application of a standard method to the equations with reaction kinetics. The modified flux-corrected transport method for the Eulerian equations is a flux-limiter method based on a convex combination of low-order and high-order schemes. The similarity solutions of the model equations for an idealized case of instantaneous release of reactive radionuclide on the ocean surface were obtained. It was found that the dispersion of reactive contamination caused by reversible phase transition can be much greater than caused by diffusion. The solutions using both numerical methods are consistent with the analytical similarity solution even at zero diffusivity. The scavenging of the <sup>239,240</sup>Pu that was introduced to the ocean surface due to the fallout from past nuclear weapon testing was simulated. The results of the simulation agreed with observation data in the north-western Pacific Ocean. The importance of the scavenging by both the large fast-sinking particles and small particles slowly sinking and dissolving with depth due to the biochemical processes was shown.</p>

Amorphous Silicon Oxynitride-Based Powders Produced by Spray Pyrolysis from Liquid Organosilicon Compounds

Silicon oxynitrides (SiOxNy) have many advantageous properties for modern ceramic applications that justify a development of their new and efficient preparation methods. In the paper, we show the possibility of preparing amorphous SiOxNy-based materials from selected liquid organosilicon compounds, methyltrimethoxysilane CH3Si(OCH3)3 and methyltriethoxysilane CH3Si(OC2H5)3, by a convenient spray pyrolysis method. The precursor mist is transported with an inert gas or a mixture of reactive gases through a preheated tube reactor to undergo complex decomposition changes, and the resulting powders are collected in the exhaust filter. The powders are produced in the tube at temperatures of 1200, 1400, and 1600 °C under various gas atmosphere conditions. In the first option, argon Ar gas is used for mist transportation and ammonia NH3 gas serves as a reactive medium, while in the second option nitrogen N2 is exclusively applied. Powder X-Ray Diffraction (XRD) results confirm the highly amorphous nature of all products except those made at 1600 °C in nitrogen. SEM examination shows the spheroidal particle morphology of powders, which is typical for this method. Fourier Transform Infrared (FT-IR) spectroscopy reveals the presence of Si–N and Si–O bonds in the powders prepared under Ar/NH3, whereas those produced under N2 additionally contain Si–C bonds. Raman spectroscopy measurements also support some turbostratic free carbon C in the products prepared under nitrogen. The directly determined O- and N-contents provide additional data linking the process conditions with specific powder composition, especially from the point of view of oxygen replacement in the Si–O moieties formed upon initial precursor decomposition reactions by nitrogen (from NH3 or N2) or carbon (from the carbonization of the organic groups).

Effect of carbon on the electrical resistivity of Ni – Al intermetallic alloy synthesized by an electrothermal explosion under pressure

In this paper, we studied the effect of carbon (3 wt. %) on the electrical resistivity of materials based on Ni − Al and Ni – Al − C synthesized by the electrothermal explosion in the temperature range 300 – 1300 K in a vacuum of 2·10–3 Pa. During an electrothermal explosion, a Ni – Al-based melt is formed in a powder reactive medium, in which carbon is dissolved. It is shown that during the crystallization of the final product, due to its low solubility in NiAl, carbon is located on the surface of intermetallic NiAl grains in the form of multilayer graphite nanofilms 50 – 80 nm thick, filling the intergranular space. It is shown that the synthesized materials have a metallic conductivity, and the electrical resistivity in the measured temperature range of 300 – 1300 K increases monotonically for the Ni – Al-based alloy from 16 to 40 mW·cm and for the carbon-containing Ni – Al – C material from 22 to 60 mW·cm. The temperature coefficient of resistance (TCS) also increases from 1.45·10–3 K–1 for NiAl to 1.77·10–3 K–1 for NiAl/C. The slope of the resistivity curves in the studied temperature range of 300 – 1300 K remains constant and is well described by a linear function.

Initial Validation of a Replicated Field-scale Denitrifying Bioreactor Facility in a Boreal Environment

Denitrifying bioreactor technology, where a solid carbon source (woodchips) acts as a reactive medium to intercept agricultural tile drainage water, has been successfully used to convert N (NO3-) to di-nitrogen (N2) gas. Four replicated field-scale (24 m long x 3 m wide x 1 m deep), bioreactors were built and operated at the St. John’s Research and Development Centre and were successful at removing a notable amount of nitrate (N) from agricultural subsurface drainage water. The objective of this study was to investigate the internal flow dynamics of one of these field-scale bioreactors as a proxy for the others. The hydraulic conditions in the bioreactor system developed differently than expected; asymmetric flow rates led to long average hydraulic retention time (HRT) and a highly dispersed residence time distribution, which was revealed by a sodium chloride tracer test. To measure the internal flow a known amount of sodium chloride (salt) was added to water before it entered the bioreactor and samples were collected in 30 minutes intervals. The temperature of water samples taken from the inlet, outlet, and sample ports ranged from 14.5 to 18.4°C With a N removal of 62 to 66% the bioreactor proved at the same time to be very effective under the boreal environment of Newfoundland and Labrador (NL). Mass removal rate (MRR) was calculated to evaluate the performance of woodchip bioreactor. The average MRR was 3.87 gm-3day-1 and the highest was 7.19 gm-3day-1 respectively. The theoretical retention time was calculated to be approximately 10.64 h based on the active flow volume, the length and depth of the system. In comparison the observed retention was 18.18 h

The Chemical Deposition of Polypyrrole at a Copper Surface Varying Concentrations of Salicylic Acid in the Reactive Medium

The in situ chemical deposition of polypyrrole (Ppy) in presence of different concentrations of salicylic acid (SA) directly at copper 99.9% surface in ethanol solution using hydrogen peroxide as catalyst was studied. In all the concentrations, 50.0, 25.0, 12.5 and 6.25 mmol L-1 the polymerization was possible. The layer formed on the copper surface showed to be adherent and homogeneous. Its morphology presented as compact microspheres. The polarization curves showed a positive displacement in the corrosion potential of copper with undoped Ppy when compared to the polished copper surface. Copper surfaces containing doped Ppy-SA also showed an increase to the positive direction in the corrosion potential and the corrosion current density decreases more sharply in the presence of SA as dopant. These results indicated that Ppy+SA can act as a protective layer on copper surface and improve the corrosion protection. The protection efficiency of the coating was Cu surface < Cu+Ppy < Cu+Ppy+SA 50.0 < Cu+Ppy+SA 25.0 < Cu+Ppy+SA 12.5 < Cu+Ppy+SA 6.25 mmol L-1.

Hydrothermal Treatment of Vegetable Oils and Fats Aiming at Yielding Hydrocarbons: A Review

According to the International Air Transport Agency (IATA), the aviation industry causes 2% of GHG emissions. As a result, goals such as improving aircraft efficiency by 1.5% per year and achieving carbon-neutral growth by 2020 were established. In this circumstance, fuels produced from biomass seem to be a promising route. There are many routes available to convert biomass into renewable fuels such as pyrolysis, hydroprocessing, transesterification, hydrothermal processes, and steam reforming. In this study, one reports a review of hydrothermal technologies. This review reports recent information about hydrothermal processes using water in sub- and supercritical states. This article introduces some concepts of the hydrothermal processes, advantages, and different types of feedstock adopted. The parameters which have an influence on hydrothermal processes such as temperature, pressure, particle size, catalyst, biomass/water ratio, and reaction time are illuminated. Water characteristics in sub- and supercritical conditions are discussed as a highly reactive medium to increase the affinity for the extraction of value-added compounds. Additionally, this review splits and details the reaction schemes that take place under hydrothermal conditions. Finally, it introduces recent research and development (R&D) trends in the hydrothermal process of fatty acids and triglycerides.