Counterflow Combustion of Micro Organic Particles

The structure of counterflow premixed flames in an axisymmetric configuration, containing uniformly distributed volatile fuel particles, with nonunity Lewis number of the fuel are examined. It is presumed that the gaseous fuel, produced from vaporization of the fuel particles, oxidizes in the gas phase and the fuel particles do not participate in the reaction. The analysis is carried out in the asymptotic limit for large values of Zeldovich number.A one-step reaction is assumed. The flame position is determined andthe effect of Lewis number change on fraction distribution is investigated

The Effect of Thermophoresis on Flame Propagation in Nano-Aluminum and Water Mixtures

This study investigates the important role of thermophoresis in flame propagation speed of nano-sized aluminum particles and water mixtures. To this aim, a one-dimensional steady state model was developed based on mass and energy conservation equations considering the effect of thermophoresis. In order to simulate the flame propagation speed of nano-sized aluminum particles and liquid water mixtures, the flame structure (the computational domain) was divided into three zones: liquid water zone, preheat zone and reaction zone. The governing conservation equations were solved numerically using a finite-difference method. The predicted results were in reasonable agreement with literature data for the flame propagation speed. The modeling results demonstrated that although the effect of thermophoresis is negligible at micro-scales, it cannot be ignored for nano-sized particles. Furthermore, as the particle size decreases and the equivalence ratio and initial mixture temperature increases; the effect of thermophoresis on the flame propagation speed becomes more significant

Effect of Radiation Heat Loss and Ventilation on Dust Explosions in Spherical Vessels

The flame propagation through a coal dust-air mixture in a spherical vessel was studied by means of a one-dimensional, Arrhenius-type kinetics and quasi-steady model. The model includes the evaporation of the volatile matter of dust particles into a known gaseous fuel (methane) and the single-stage reaction of the gas-phase combustion. Effect of venting devices as safety idea and the radiation heat loss, as very affecting phenomenon on flame propagation speed, flame temperature and pressure were studied. The radiation heat losses occur between the reaction zone and the surrounding wall. Influence of dust concentration and dust volatility on dust explosion parameters has been analyzed. The pressure-time curves that are generated with this model show a good similarity with those measured in practice. The model can represent a useful framework to be employed in organic dust combustion. This research can be valuable in the development of alternative fuels; and it can be used by the fire safety and control industry

Modeling Flame Propagation of Coal Char Particles in Heterogeneous Media

In the present research, combustion of a quiescent coal char particle cloud has been studied in the media with spatially discrete sources by means of numerical approach. A thermal model based on diffusion-controlled regime of coal char particles has been generated in order to estimate the characteristics of flame propagation in heterogeneous media. The model uses discrete heat sources to analyze dust combustion of particles with the diameter of 50 μm. Oxygen and Nitrogen have been considered as the main oxidizer and the inert gas, respectively. Flame propagation speed in various dust and oxygen concentrations has been studied. Flame speed as a function of particle size has been investigated and comparison between cases with and without consideration of radiation effect has been made. Furthermore, minimum ignition energy as a function of dust concentration for different particle sizes has been studied. Results show a reasonable compatibility with the existing experimental data

Study on hybrid combustion of aero-suspensions of boron-aluminum powders in a quiescent reaction medium

The present research deals with a hybrid combustion of aluminum/boron dust particles in a heterogeneous quiescent reaction medium with spatially discrete heat sources. A developed thermal model is employed to estimate flame propagation speed in a reaction medium. The burning velocity and minimum ignition energy are studied parametrically as a function of dust concentration and particle diameter for different percentages of boron powder in a hybrid mixture of aluminum/boron dust cloud. The model shows that the addition of boron powder as a component of the mixture decreases the burning rate and causes a higher amount of minimum ignition energy needed for ignition, owing to the role of boron as a heat sink. Comparison of the simulation results with the available experimental data shows that the model captures the flame propagation speed as a function of particle concentration, except at very low concentrations

Topical effectiveness of different concentrations of nanosilver solution on Leishmania major lesions in Balb/c mice

Background & objectives: Cutaneous leishmaniasis is an infection caused by protozoan genus Leishmania. Althoughglucantime is commonly used for the treatment of leishmaniasis, it has some side effects including increased liverenzymes and electrocardiogram changes. In addition, the drug is expensive, the injection is painful, and researchshows that resistance of parasite to glucantime is growing in different parts of the world. Therefore, scientists arepaying more attention to develop new drugs such as nanosilver solution. The present study is an attempt toevaluate the in vivo topical effects of different concentrations of nanosilver solution in the treatment of leishmaniasislesions.Methods: In all, 90 female Balb/c mice aged 6–8 wk were infected with 2×106 viable stationary-phase promastigotesin the base of tail. Different concentrations (60, 80, 120, 130 and 2000 ppm) nanosilver solution were used in thepresent study to test the efficacy in the treatment of lesions. Clinical control of the infection trends was conductedweekly for 5 wk by measuring lesion diameter with standard Kulis-Vernieh. Data were analyzed by paired t-test,analysis of variance (ANOVA), and Tukey test.Results: Mean lesion diameter pre- and post-treatment did not significantly differ between different treatmentgroups (p >0.05). Likewise, a significant difference in splenic parasite load was also not observed between differenttreatment groups.Interpretation & conclusion: Based on our results, different concentrations of nanosilver are ineffective in reducingmean sizes of lesions

A simplified mathematical study of thermochemical preparation of particle oxide under counterflow configuration for use in biomedical applications

This study mathematically presents a counterflow non-premixed thermochemical technique for preparing a particle oxide used for cancer diagnosis and treatment. For this purpose, preheating, reaction, melting, and oxidation processes were simulated considering an asymptotic concept. Mass and energy conservation equations in dimensional and non-dimensional forms were solved using MATLAB®. To preserve the continuity in the system and calculate the locations of melting and flame fronts, promising jump conditions were derived. In this research, variations in flame temperature, flame front location and mass fractions of the particle, particle oxide and oxidizer, with position, Lewis number and initial temperature of the particles were investigated. The simulation results were compared with those obtained from an earlier experimental study under the same conditions. Regarding the comparison, an appropriate compatibility was observed between the results. Based on the simulation results, flame temperature was found to be about 1310 K. Positions of flame and melting fronts were found to be − 1.8 mm and − 1.78 mm, respectively

An experimental and analytical study of laminar dust flame propagation

The fundamental properties of dust flame propagation have been studied experimentally and theoretically. Experiments were carried out in a Pyrex tube having a 5 cm inside diameter and a length of 1.2 meters. The dust dispersion system in the present experiment has been demonstrated to produce a laminar flow with uniform dust concentration. It is observed that the propagating flame exhibits a truly laminar character of propagation. Propagation and quenching of dust-air flames were measured for aluminum dust for a relatively wide range of dust concentration. It was observed that the process of the dust flame propagation in the tube can be divided into three different stages: laminar flame, oscillating flame and turbulent accelerating flame. During the first stage, the flame propagates with approximately constant speed and the flame is laminar. This stage is about 1/3 to 1/2 of the tube length and the shape of the flame front during this phase is close to the usual parabolic shape. In the second stage, flame starts to oscillate. Bright regular flashes alternate with stages when the flame is almost invisible. The third stage of the flame propagation can be observed only if the dust concentration is close to or higher than stoichiometric. The quenching distance and flame velocity of an aluminum dust flame under different initial oxygen concentrations and with different inert gases such as helium and nitrogen were also measured. When the amount of the initial oxygen concentration decreases, both the quenching distance and the lean limit increase, while the flame velocity decreases. On the other hand, after using helium as the inert gas of the mixture, it was observed that the whole value of the quenching distance, the lean limit, and the flame velocity increase. However, the objective is to understand the mechanism of the dust flame propagation. Theoretical models have also been developed to correlate the data to achieve a better understanding of the propagation mecha

Flame propagation of micron sized aluminum dust cloud in oxygenated media with different neutralize gas

In this research an analytical study has been conducted to determine flame propagation speed and quenching distance of aluminum dust particle in an oxygenated medium with different neutralized gas including nitrogen, argon, and helium which acts as the oxidizer carrier gas. Flame propagation speed as a function of aluminum dust cloud concentration has been studied based on a thermal diffusion model. Additionally quenching distance for different dust particle concentration in the intended neutralize gas is investigated. Reasonable agreement between the present analytical model and experimental results reported in literature has been observed in terms of flame propagation speed in different dust concentrations