Nano-sized Aluminum Particles Research Articles

Numerical study on the characteristics of a nano-aluminum dust-air jet flame

Nano-sized aluminum dust is quite attractive in the application scenarios with limited residence time. This study simulated an aluminum nanoparticle-air jet flame in a burner that was proposed to characterize the mixing and burning properties of dust and air in a classical ramjet configuration. The model considers the flow of gas phase by employing three-dimensional multicomponent Navier-Stokes equations, and the aluminum particles via the Lagrange approach. A combustion sub-model was developed to characterize the heat convection, radiation and combustion processes of nano-sized aluminum particles. Thereafter, the model was validated by comparing with experimental results of dust jet flow and aluminum particle combustion. With the present model, the characteristics of flow field, and variations of particle temperature, heat release and statuses etc. were examined in detail, by which the mixing zone and flame structure were defined. The results showed that the nano-aluminum particles in the inner mixing layer were firstly ignited by the hot co-flow air and burned, and these particles in the core jet region were ignited downstream. Once the aluminum particles were ignited, they burned out promptly in this burner. The effects of particle size were evaluated, and the results show that the lengths of mixing layer and reaction zone, as well as the width of reaction zone reduce with decreasing particle size, whereas the width of mixing layer stays the same.

Cellular detonation propagation and degeneration in bi-disperse gas suspensions of micron- and nano-sized aluminum particles

Cellular detonation flows in bi-disperse oxygen suspensions of micron-, submicron-, and nano-sized aluminum particles are studied numerically on the basis of the semiempirical model of detonation. The transition from diffusion-limited combustion of micron-sized particles to the kinetic combustion regime of nano-sized aluminum particles is taken into account. The influence of the particle size and the mass fraction composition on the cellular detonation structure is analyzed. In micron- and submicron-sized bi-disperse mixtures, a degeneration of the cellular structure, with weakening and disappearance of the transverse waves, is observed for intermediate values of the mass fraction ratio. In bi-disperse mixtures of micron- and nano-sized particles, a gradual change in the detonation cell size and maximal pressure values with a variation of the mass fraction ratio is obtained. The numerical results are confirmed by acoustic analysis on the basis of Barthel’s method, which predicts the existence or absence of a regular system of transverse waves.

Modeling of Cellular Detonation in Gas Suspensions of Two Fractions of Aluminum Nanoparticles

Cellular detonation in suspensions of two fractions of submicron and nano-sized aluminum particles is studied by numerical methods. Approaches of mechanics of heterogeneous media are used. The transition from the continuum to free-molecular regime of the flow around the particles is taken into account in the processes of interphase interaction. Particle combustion is described within the framework of the previously developed model of reduced kinetics. The results calculated for two-dimensional flows in a plane channel reveal significant differences from suspensions of two fractions of microparticles, where degeneration of transverse waves is observed. In the present study, weakly regular and irregular cellular structures are formed, which is also confirmed theoretically on the basis of the acoustic analysis based on the method proposed by Barthel.

Effect of non-spherical particles on burning behavior during aluminum combustion

The shape of an aluminum particle is assumed to be spherical or an equivalent sphere during the combustion process. Such an assumption lacks objectivity and leads to unreasonable approximations of burning efficiency and performance. To investigate the influence of non-spherical particles on burning behavior, this study focused on a theoretical and experimental investigation of the combustion of nanoscale aluminum ellipsoidal particles. Models for prolate and oblate spheroids in aluminum combustion were established to explore combustion properties such as mass release rate, linear burning rate, burning rate, and burnout time. To validate the theoretical results, combustion experiments were conducted on three samples. Reasonable agreement between the results of numerical simulation and experimental findings was obtained in terms of the particle burning characteristics. It was found that particle morphology (such as prolate or oblate spheroid shape) and size play a significant role in the combustion performance of nanosized aluminum particles.

Mechanical Performance of glass/epoxy composites enhanced by micro- and nanosized aluminum particles

In this article, the effects of using nanometer and micrometer-sized aluminum particles in glass fiber reinforcement epoxy composites have been studied. The study evaluates the mechanical properties improvement with the addition of nanometer and micrometer-sized aluminum particles to glass fiber reinforcement epoxy composites. The combination of aluminum and woven glass fibers provide high potential for the modification of the epoxy matrix. The composites were produced by hand lay-up technique. The glass fiber volume fraction was kept constant at 35%, while the contents of aluminum particles were increased from 0.2 to 4 wt%. The developed composites showed enhanced tensile, flexural, hardness, wear, and impact behavior as compared to glass fiber reinforcement epoxy. An enhancement of 27% was attained in tensile strength with glass fiber reinforcement epoxy filled with 2 wt% aluminum nanoparticles; however, adding 4 wt% nanometer-sized aluminum particles showed an improvement of 114%, 116%, 21%, 52.2%, 21.4%, 76.6% in tensile elongation, toughness, tensile modulus, flexural strength, flexural strain, flexural modulus, respectively as compared to neat glass fiber reinforcement epoxy. Increasing the nanometer-sized aluminum particles in glass fiber reinforcement epoxy composites to 4 wt% reversed the improvement trend in tensile strengths, wear, and hardness. However, increasing the micrometer-sized aluminum particles to 4 wt% has shown fair improvement in all used aluminum loadings. Microscopy results showed that the aluminum particles were well dispersed in the epoxy matrix. However, a higher weight fraction of nano-aluminum in the epoxy had promoted little agglomerations.

Modeling of Cellular Detonation in Gas Suspensions of Submicron and Nano-Sized Aluminum Particles

Cellular detonation in monodisperse suspensions of submicron and nano-sized aluminum particles is numerically simulated. Approaches of mechanics of heterogeneous media are applied. The transition from the continuum to free-molecular regime of the flow around the particles is taken into account in the processes of interphase interaction. Particle combustion is described within the framework of the semi-empirical model developed previously. Results calculated for two-dimensional flows in a plane channel for suspensions of aluminum particles with the particle size ranging from 1 µm to 100 nm are presented. The regular structure of cellular detonation is found to transform to an irregular structure as the particle size decreases. An increase in the peak pressure and enlargement of the detonation cell are also noted, which is attributed to enhancement of the activation energy of reduced kinetics caused by the transition to the kinetic regime of combustion of aluminum particles.

Ignition and combustion of nano-sized aluminum particles: A reactive molecular dynamics study

Combustion mechanism of nano Al particles remains controversies for years. In this paper, we use ReaxFF molecular dynamics simulations to study thermodynamic and structure properties of Al particles from ignition to combustion. Two typical core–shell nano Al models with different oxide shell thickness are studied. Effect of radiative heat transfer is also considered in the combustion stage. Our results show that no shell cracks are observed during both heating and burning periods. The oxide shell hinders the thermal diffusion of core Al atoms and causes the abnormal melting rule. The stress variations at the core–shell interface are the most dramatic during the heating period. The combustion processes are controlled by diffusion behaviors of components in particles and external oxygen molecules. Detailed structural evolution processes are studied by displacement magnitude analysis. Particle with thinner shell has a shorter ignition delay and a higher combustion temperature which directly affect the radiative heat transfer rate during the combustion period.

Modeling of Cellular detonation in Gas Suspensions of Submicron and Nano-Sized Aluminum Particles

Modeling of Cellular detonation in Gas Suspensions of Submicron and Nano-Sized Aluminum Particles

Problems of Closing Models that Describe Detonation of Gas Suspensions of Ultrafine Aluminum Particles (Review)

Various publications dealing with physicomathematical modeling ol detonation processes in gas suspensions ol line, submicron, and nano-sized aluminum particles within the framework ol mechanics ol continuous and heterogeneous media are reviewed. Important issues ol the description ol thermal dynamics, transport properties, and ignition mechanisms are discussed. Specific features of combustion regimes of micron- and nano-sized particles are considered. Closing relations for a semi-empirical model of detonation of suspensions of aluminum nanoparticles in oxygen are presented.

Numerical Simulation of Combustion of a Metallized Composite Solid Propellant with Additives of Nanosized Aluminum Particles

The paper presents a numerical simulation of combustion of a metallized composite solid propellant with additives of micron-and nanosized aluminum particles. The model takes into account the thermal effect of decomposition of the condensed phase, convection, diffusion, the exothermic chemical reaction in the gas phase, heating and combustion of aluminum particles in the gas flow, the flow of combustion products, the particle velocity lag relative to the gas. The effect of the Al particle size and mass fraction, emitted from the burning surface, on the burning rate is also taken into consideration.

Modeling of Plane Detonation Waves in a Gas Suspension of Nano-Sized Aluminum Particles

Modeling of Plane Detonation Waves in a Gas Suspension of Nano-Sized Aluminum Particles

Comments on: “Combustion of nano-sized aluminum particles in steam: Numerical modeling”, by V.B. Storozhev and A.N. Yermakov

This comment points out the large discrepancy between the predictions of the recently published model by Storozhev and Yermakov (Storozhev and Yermakov, Combust. Flame 162 (2015) 4129–4137) and the large body of accumulated literature on aluminum combustion. Their model predicts burning times between 40-63 ms for a cloud of nanometric aluminum particles (20 or 50 nm) burning in steam at initial temperatures around 2300 K. These predictions are roughly two orders of magnitude larger than the measured combustion times of micron and submicron aluminum particles from various experiments, which are on the order or hundreds of microseconds to milliseconds. Experimentally measured flame speeds of aluminum flames in the products of hydrocarbon flames, and the burn rates of metal-water propellants, also point to much faster burning rates of aluminum particles in steam than predicted by this model. As such, the predictions of the model by Storozhev and Yermakov cannot be reconciled with the available experimental evidence.

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.

Combustion of nano-sized aluminum particles in steam: Numerical modeling

A model of the dynamics and mechanism of combustion of an ensemble of nanoscale aluminum particles in a steam is theoretically studied for adiabatic conditions. The formation of condensed phase is modeled for conditions when the homogeneous nucleation of gaseous Al2O3 species, processes of condensation/evaporation and coagulation of particles are taken into account. The model is used for studying the effects of the particle size, equivalence ratio, and chemical kinetics on the burning characteristics of aluminum-particle/steam mixtures. The calculated rate of combustion is limited by the rate of condensation growth of particles contained thermally unstable Al2O3 species. The details of the mechanism of interaction of the gas-phase reactions and the formation of particles are discussed. The results of numerical calculations are compared with experimental results of nano-aluminum dust combustion.

Combustion of Gelled Propellants Containing Microsized and Nanosized Aluminum Particles

The combustion behaviors of gel fuels containing micro- and nanosized aluminum particles were investigated in a pressurized chamber under typical ramjet conditions. Condensed combustion products were sampled in the jet plume behind the exit nozzles with two different rapid-insertion probes. The chemical composition of the samples was determined, and the structure of the sampled combustion products was studied with microscopic techniques. The formation of large aggregates of aluminum was observed, which left the combustion chamber with limited oxidation. The formation of such aggregates could explain why the substitution of micro-Al with nano-Al did not lead to the expected increase in combustion efficiency.

나노 및 마이크로 입자 알루미늄의 폭발 특성

마이크로 크기의 알루미늄 분진의 폭발 특성에 대한 연구는 많이 조사되어 왔지만 나노 크기의 알루미늄 분진에 대한 연구는 매우 적다. 본 연구에서는 나노 및 마이크로 크기의 알루미늄 분진 (70 nm, 100 nm, <TEX>$6{\mu}m$</TEX>, <TEX>$15{\mu}m$</TEX>)이 분진폭발특성에 미치는 영향을 20 L 폭발시험 장치를 사용하여 실험적으로 조사하였다. 부유 상태의 알루미늄 분진의 입자 크기가 감소하면, 나노 크기에서의 알루미늄 분진의 폭발하한농도(LEC)는 마이크로 크기의 알루미늄분진보다 감소하였다. 나노 크기의 알루미늄 분진에서의 폭발특성은 마이크로 크기의 알루미늄 분진과 명확한 폭발성의 차이를 보이지 않았다. 투과 전자 현미경(TEM )에 의해 나노 크기의 알루미늄 입자의 관찰로부터 입자 간의 응집성의 증가가 나노 알루미늄 분진의 폭발성에 영향을 미칠 수 있을 것으로 추정되었다. Explosion characteristics of micro-sized aluminum dusts had been studied by many researchers, but the research of nano-sized aluminum dusts were very insufficient. In this study, an experimental investigation was carried out on the influences of nano and micro-sized aluminum dusts (70 nm, 100 nm, <TEX>$6{\mu}m$</TEX>, <TEX>$15{\mu}m$</TEX>) on dust explosion properties of aluminum particles by using 20 L explosion apparatus. With decreasing of particle size in suspended aluminum dusts, the LEC (lower explosion concentration) of nano-sized aluminum is lower than that of micro-sized aluminum. The particle size change of nano-sized aluminum dusts seems no obvious explosion differences than that of micro-sized aluminum dusts. From the observation of nano-sized aluminum particles by TEM (Transmission Electron Microscopy), it is estimated that increase of particles aggregation may have effects on the explosion characteristics of aluminum nanopowders.

Investigation of particle size effect on flame velocity in the combustion of nano/micron-sized aluminum particles in air

It is observed that a diffusion-controlled mechanism applied to the burning of micron-sized particles is not applicable to the combustion of nano-sized particles burning under kinetically controlled conditions. Furthermore, when heat transfer occurs between micron-sized particles and air, Nusselt number can be assumed to be constant and equal to 2, while this number is a function of Knudsen number when heat transfer occurs between nano-sized particles and air. Ignition temperatures of micron- and nano-sized particles are also different. In this article, mass and energy conservation equations for both particle and gas phases are solved. By doing so, flame velocity is obtained. Afterwards, with respect to different combustion characteristics of micron-and nano-sized particles such as ignition temperature, burning time, and Nusselt number, the effect of particle size on the flame velocity of aluminum particles combustion in air is studied and compared with experimental and numerical results. At the equivalence ratio of 0.85, it is shown that flame velocity is proportional to d−0.94 and d−0.56 for micron- and nano-sized aluminum particles, respectively.

Pyrophoricity of nano-sized aluminum particles

The temperature histories are calculated for spherical nano-sized aluminum particles with no protective oxide shell inserted in air at 300 K. In calculations, initial particle temperatures varied and the minimum initial temperature leading to the particle ignition was determined. The particle, initially without any oxide coating, was assumed to react adiabatically forming a monomolecular oxide coverage; the following oxidation was assumed to be governed by the Cabrera–Mott reaction mechanism. Convection and radiation heat losses were considered. Convection was accounted for using a transition regime heat transfer model by Fuchs. Aluminum particles with diameters less than about 68 nm are predicted to be pyrophoric, e.g., ignite without appreciable initial pre-heating.

Mathematical modeling of melting of nano-sized metal particles

A physicomathematical model is developed to describe melting of nano-sized aluminum and gold particles within the framework of a single-phase Stefan problem with allowance for the experimentally established fact of melting temperature reduction with decreasing particle radius. The time of melting of aluminum and gold nanoparticles is determined as a function of the particle radius and ambient temperature. At identical ratios of the ambient temperature to the melting temperature, the ratio of the time of melting of aluminum particles to the time of melting of gold particles is found to remain approximately constant and equal to 4.

The synthesis of nanosized aluminum particles by the levitation-in-flow method and an analysis of their particle size distribution

This study deals with the levitation-in-flow method for synthesizing ultrafine nanosized metal powders. The dependence of the average size of particles on the pressure of the medium is determined from a refined mathematical model describing the formation of metal particles during the homogeneous condensation of the metal vapor in a temperature boundary layer at an evaporating metal droplet blown around by an inert gas. Using aluminum as an example, theoretical curves of the particle size distribution are compared with experimental histograms. The theoretical and experimental results are in good agreement.