A model of laminar flames in droplet suspensions

A mathematical model of steady laminar flame propagation through a suspension of liquid droplets was proposed, and numerical calculations within the framework of this model were performed. The model is constructed based on one-dimensional differential equations of the theory of laminar flames in homogeneous gaseous mixtures in conjunction with the theory of droplet burning in uniform monodisperse suspensions. The chemical process was described using a multistage kinetic scheme. A comparison of model predictions with the available experimental data demonstrated satisfactory agreement.     

Breakup of an uncharged droplet in an electrostatic field

The breakup of an uncharged electrically conducting liquid dropet placed in a uniform electrostatic field into two daughter droplets caused by strong nonspheroidal deformation is qualitatively analyzed by applying the principle of minimum potential energy under spontaneous virtual variations of the droplet’s state. It is shown that the breakup mechanism involves asymmetric mass distribution among the daughter droplets, which are found to be stable with respect to their respective intrinsic charges.     

Production of magnetic microspheres by ultrasonic atomisation

Magnetic microspheres, with mean particle sizes from 23 to 32 μm were produced by the ultrasonic atomisation of a suspension of magnetite particles, of approximately 200 nm diameter, in a solution of poly–l–lactic acid (PLLA). The mean particle diameter and the width of the particle diameter distribution both increased with increasing magnetite concentration. The particles appear to be suitable for magnetic hyperthermic treatment of liver cancers, with the hysteresis loop areas increasing linearly with nominal magnetite concentration up to 30 wt% magnetite.     

Scattering of light waves by electron electrostatic waves in laser produced plasmas

The propagation of light waves in an underdense plasma is studied using one-dimensional Vlasov-Maxwell numerical simulation.It is found that the light waves can be scattered by electron plasma waves as well as other heavily and weakly damping electron wave modes,corresponding to stimulated Raman and Brilluoin-like scatterings.The stimulated electron acoustic wave scattering is also observed as a high scattering level.High frequency plasma wave scattering is also observed.These electron electrostatic wave modes are due to a non-thermal electron distribution produced by the wave-particle interactions.The collision effects on stimulated electron acoustic wave and the laser intensity effects on the scattering spectra are also investigated.     

Sound propagation in saturated gas-vapor-droplet suspensions with droplet evaporation and nonlinear relaxation

The Sound attenuation and dispersion in saturated gas-vapor-droplet mixture in the presence of evaporation has been investigated theoretically. The theory is based on an extension of the work of Davidson [J. Atmos. Sci. 32(11), 2201-2205 (1975)] to accommodate the effects of nonlinear particle relaxation processes of mass, momentum and energy transfer on sound attenuation and dispersion. The results indicate the existence of a spectral broadening effect in the attenuation coefficient (scaled with respect to the peak value) with a decrease in droplet mass concentration. It is further shown that for large values of the droplet concentration the scaled attenuation coefficient is characterized by a universal spectrum independent of droplet mass concentration.     

Fabrication of nano-structured gold films by electrohydrodynamic atomisation

A monodisperse alcosol containing 0.1 wt. % 15 nm gold particles was subjected to controlled flow through a metal capillary exposed to an electric field at the ambient temperature to generate an electrohydrodynamic jet, which subsequently disintegrated into droplets. A silicon substrate was used to collect the droplets and prepare gold films. By varying the deposition time, we have prepared gold films in the thickness range of ∼500–∼ 2000 nm in a maximum spray time of 450 s. This is a significant achievement considering the initial concentration of gold and the spray time involved. The characteristics of the jet, droplets and films prepared were evaluated using advanced analytical techniques. PACS 81.15.Rs; 81.15.-z; 81.07.-b; 81.20.-n; 68.55.jd     

静电放电电磁脉冲模拟装置

介绍了静电放电电磁脉冲（ESD EMP）的特性。研究了用ESD 模拟器产生ESD EMP的方法,并给出了ESD EMP的时域波形和频谱。在研究ESD模拟器的基础上,首次通过ESD模拟器和GTEM室的结合,在GTEM室内产生了均匀的、重复性和线性好的ESD EMP。实验表明,用这种装置能够实现对静电放电电磁脉冲的实验室模拟。实现了人们用GTEM室产生ESD EMP的梦想。     

静放电电磁脉冲模拟装置

介绍了静电放电电磁脉冲（ESD EMP）的特性，研究了用ESD模拟器产生ESD EMP的方法，并给出了ESD EMP的时域波形和频谱。在研究ESD模拟器的基础上，首次通过ESD模拟器和GTEM室的结合，在GTEM室内产生了均匀的，重复性和线性好的ESD EMP。实验表明，用这种能够实验对静电放电电磁脉冲的实验室模拟，实验了人们用GTEM室产生ESD EMP的梦想。     

静电放电电磁脉冲模拟装置

 介绍了静电放电电磁脉冲（ESD EMP）的特性。研究了用ESD 模拟器产生ESD EMP的方法，并给出了ESD EMP的时域波形和频谱。在研究ESD模拟器的基础上，首次通过ESD模拟器和GTEM室的结合，在GTEM室内产生了均匀的、重复性和线性好的ESD EMP。实验表明，用这种装置能够实现对静电放电电磁脉冲的实验室模拟。实现了人们用GTEM室产生ESD EMP的梦想。     

Electrospray of fine droplets of ceramic suspensions for thin-film preparation

An electrostatic atomization technique has been developed to generate ultra-fine spray of ZrO₂ and SiC ceramic suspensions in a range of 4–5 μm with a narrow size distribution (1–9 μm). The aim of this work is to generate fine spray of ceramic suspensions for the preparation of uniform thin films of these ceramic materials on substrates. Thin-film formation using electrostatic atomization process allows one to tightly control the process while meeting the economics in comparison with some other competing process technologies such as chemical vapour deposition, physical vapour deposition and plasma spray, etc. Preliminary results have shown that for low through put atomization, the cone-jet is the most suitable method to produce a fine charged aerosol with a narrow size distribution. It was found that the droplet size of the spray is in the range of a few micrometers with a narrow size distribution and that droplet size and spray current obey theoretical prediction of scaling law. As prepared ZrO₂ and SiC thin films were observed to be homogenous with a particle size of less than 10 μm.     

压电陶瓷电源在静电演示实验中的应用

自行研制了压电陶瓷电源,具有体积小,效率高,无电磁噪声,无电磁式绕组及不可燃烧、安全性高,受外界影响小等特点. 将压电陶瓷电源应用于静电演示实验,取得了较好的教学效果.     

Influence of Ga coverage on the sizes of GaAs quantum dash pairs grown by high temperature droplet epitaxy

We investigate the formation of GaAs quantum dash pairs with different coverages by droplet epitaxy. The GaAs quantum dash pairs of various sizes are fabricated by high temperature droplet epitaxy. Dual‐sized quantum dash pairs are observed along $[01\bar 1]$ orientation. Depending on the Ga cov‐ erage, the width of the quantum dash pairs can be tuned from ～100 nm to ～300 nm while keeping the height in the range of 4 nm to 10 nm. The coverage dependence of quantum dash pairs is also confirmed with photoluminescence measurement. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparative study of morphology and surface composition of Al–Cr–Fe alloy powders produced by water and gas atomisation technologies

The morphology and surface composition of Al–Cr–Fe alloy powders of 0–63 and 63–100 μm size fractions, produced by gas and water atomisation, have been studied by scanning electron microscopy and Auger electron spectroscopy. While gas atomised particles are of spherical shape, water atomised powders are usually irregular in shape with a complex branched relief. The morphology and composition of surface oxides have been estimated. The surface oxide film is composed of aluminium oxides/hydroxides and contains no Fe and Cr atoms. Two to five water molecules are associated with one Al₂O₃ molecule on the surface of powders. The surface oxide film has a non-uniform thickness, with thick oxide islands separated by thinner oxide film. The parameters of the surface film morphology, such as the island coverage, the oxygen content and the thin film thickness, depend on the atomisation technology used and powder size fraction. Heavily and weakly oxidised powder groups present in all powder fractions are distinguished by Auger spectra analysis. Relationships between heavily and weakly oxidised powder groups are discussed as a function of atomisation technology and size fraction.     

Evaluation of the morphology of particles produced by plasma-chemical synthesis of ceramic powders

A physicomathematical model of thermal and diffusion processes in a drop of a dilute metal salt solution during its heating in a plasma-chemical reactor for synthesizing metal oxide powders is presented. The results of numerical calculations are analyzed to assess the possible influence of the operation parameters of the reactor and the characteristics of the initial solution (precursor) on the morphology of the particles formed.     

Deposition of colloidal gold nanoparticles by fully pulsed-voltage-controlled electrohydrodynamic atomisation

Pulsed electrohydrodynamic atomisation (EHDA) of aqueous 10 nm gold colloid in a full voltage-controlled form was investigated. By using 4 µm and 20 μm nozzles, electrified fluid jet was emitted and Au nanoparticles in the jet were deposited onto a silicon substrate. Scanning electron microscopy (SEM) revealed that different morphology of the artifact was formed by using different voltages pulses. Particularly, island-liked artifact down to 10 μm can be produced regularly in the case of cone-jet mode by low voltage pulse. Our results demonstrate pulsed EHDA is a promising approach in creating micro-patterns of colloid-based nanomaterials.     

First laboratory observation of freely propagating electrostatic waves produced by intense, localized field structures

Freely propagating electrostatic waves (free modes) are observed to be produced by intense, localized field structures in laboratory measurements performed in an unmagnetized plasma in a state of strong Langmuir turbulence. The freely traveling waves conform to the Langmuir dispersion relation and have an average frequency which is approximately 11% higher than the average frequency of the localized field structures. The observations are consistent with the predictions of strong Langmuir turbulence theory.     

A discrete droplet transport model for predicting spray coating patterns of an electrostatic rotary atomizer

Electrostatic spray (E-spray) coating is widely used for coating conductive substrates. The combination of a high-velocity shaping air, an imposed electric field and charged droplets, leads to higher transfer efficiency than conventional spray coating. In this paper, a mathematical model of droplet transport in E-spray is presented which enables simulating the coating deposition rate profile. A dilute spray assumption (no particle–particle interactions) allows modeling single-droplet trajectories resulting from a balance of electrostatic force, drag and inertia. Atomization of liquid droplets is not modeled explicitly—rather an empirical correlation is used for the mean droplet size while individual droplet sizes and starting locations are determined using random distributions. Strong coupling requires the electrostatic field and droplet trajectories be determined iteratively by successive substitution with relaxation. The influences of bell-cup voltage and atomization constant on the coating deposition rate profile, mass transfer efficiency and droplet trajectories are also shown. Using individually predicted droplet trajectories and impact locations, a static coating deposition rate profiles is determined. For the parametric values considered in this paper, the predicted spray is a cone hollow with no deposition in the center, a heavy ring near the center, and a tapering of thickness toward the outer edge.     

Analysis of visual perception of light emitting diode brightness in dense fog with various droplet sizes

Road signs must provide a conspicuous signal to a wide variety of drivers over a broad range of environmental and geometric conditions. Recently, there are an increasing number of applications in which light emitting diodes (LEDs) are used as the light source, including critical transportation signaling. In the presence of fog, the resulting visual signal is disturbed due to light scattering by airborne water droplets. By measuring LED brightness with human spectral sensitivity in various densities and various droplet sizes (10, 30, 50, and 100 μm), it is understood that the particle size distribution (fog droplet size) and density of fog does affect visibility in fog. The colored LEDs that contain a yellow component had high brightness evaluation, blue component had low brightness evaluation in all densities and different droplet sizes. The result in this paper can contribute to air and land traffic safety and the prevention of accidents.     

Microbial content of aerosols produced from suspensions exposed to megahertz frequency ultrasound

A piezo-electric bowl transducer was used to generate aerosols by focusing ultrasound in the frequency range 1–7 MHz at a liquid/air interface. Atomization at the liquid surface and the production of a fountain contributed to aerosol formation. When the liquid consisted of suspensions of representatives from the viral, bacterial, and yeast groups of micro-organisms (covering a 0.2–11.5 μm size range) living organisms were isolated from the aerosols at all frequencies. The fountains were implicated as a major source of air-borne micro-organisms because significant numbers of isolates were obtained in the presence of fountains but in the absence of obvious atomization, and theoretical predictions make the sizes of droplets arising from atomization at the higher frequencies too small to have carried some of the larger organisms.     

Synthesis,droplet combustion,and sooting characteristics of biodiesel produced from waste vegetable oils

In light of the potential of fatty acid methyl ester (FAME, i.e. biodiesel) as a renewable energy source, an innovative acid catalyzed process was developed for the synthesis of biodiesel from waste vegetable oils. The synthesized biodiesels were analytically characterized for their major components, molar fraction and molecular weight of each component, the average molecular weight, and the heat of combustion. Their droplet combustion characteristics in terms of the burning rate, flame size, and sooting tendency were subsequently determined in a high-temperature, freely-falling droplet apparatus. Results show that the biodiesel droplet has higher burning rate, and that biodiesel in general has a lower propensity to soot because its molecular oxygen content promotes the oxidation of the soot precursors.