热喷涂液相合成粉末的雾化喷嘴设计

为了形成尺寸基本一致且在空间呈均匀分布的雾滴,以利于制备均匀性好、粒径分布窄的纳米颗粒,通过对单相流和两相流雾化喷嘴的对比,以及液滴的雾化过程分析,根据相关实验结果和经验公式,设计出了用于热喷涂液相合成粉末的雾化喷嘴,其雾化气输送管径为0.2mm,液料输送管径为2.0mm,二者夹角为90°。此雾化喷嘴在等离子喷涂制备TiO2纳米颗粒的实验中得到了成功应用。     

Modelling of the break up mechanism in gas atomization of liquid metals. Part I: The surface wave formation model

An integrated model of the atomization of a liquid column perturbed by a flowing gas phase is proposed. The algorithm termed Surface Wave Formation (SWF) is based on the concept of the formation of sinusoidal waves travelling along the surface of the liquid. The amplitude of such instabilities can grow exponentially under specific conditions, effectively causing the detachment of liquid particles either by shearing of part of a wave crest or by detachment of a liquid body at negative amplitude nodes. The SWF model covers both primary and secondary atomization and can in principle describe the break up of any well-defined liquid shape. Model predictions compare favourably with experimental data from close coupled atomization of metals. The implications of the SWF algorithm are important, since—unlike empirical correlations—it can predict the size distribution of particles inside a spray in space and atomization time. Future integration could include calculations of cooling histories of drops in flight.     

Effects of process parameters on surface morphology of metal powders produced by free fall gas atomization

There are a number of process parameters which affect the characteristics of metal powders produced by free fall gas atomization. In the following work effects of various process parameters like apex angle of atomizer, focal length of atomizer, number of nozzles, diameter of nozzles, diameter of liquid metal delivery tube, superheat of liquid metal and type of metal etc. were studied on their surface morphology. It was observed that shape of powder particles depends on apex angle, superheat of liquid metal, type of metal and particle size range within a powder collective. Other parameters like focal length of atomizer, number of nozzles, diameter of nozzles and diameter of liquid metal delivery tube were found to have no effect on the shape of powder particles. However, Surface porosity and solidification shrinkage were observed on almost all types of metal powders.     

大气气溶胶对混合相对流云影响的模拟研究

利用二维面对称分档云模式,讨论了气溶胶类型及浓度对混合相对流云及其降水的影响。结果表明:海洋性气溶胶谱分布在一定程度上更有利于降水的形成,随着气溶胶浓度的增加,尤其是在污染大陆性云中,暖云和冷云降水量均大幅减少。海洋性云中的大粒子和较高的过饱和度,加速了暖雨的碰撞过程和冰粒子的凝华增长;初始气溶胶浓度的增加最显著的效应是云滴数浓度和云水含量增加,云滴有效半径减小,云滴的冷却蒸发抑制对流的发展。     

Development of an Imaging System and Its Application in the Study of Cutting Fluid Atomization in a Turning Process

Airborne inhalable particulates in the workplace can represent a significant health hazard, and one of the primary sources of particles is mist produced through the application of cutting fluids in machining operations. One of the principal mechanisms associated with cutting fluid mist formation is atomization. Atomization is studied by applying cutting fluid to a rotating workpiece such as found in a turning process. In order to properly study the atomization mechanism, an imaging system was developed. This system extends the size measurement range typically achievable with aerosol sampling devices to include larger particles. Experimental observations reveal that workpiece rotation speed and cutting fluid flow rate have significant effects on the size of the droplets produced by the atomization mechanism. With respect to atomization, the technical literature describes models for fluid interaction with the rotating workpiece and droplet formation via drop, ligament, and film formation modes. Experimental measurements are compared with model predictions. For a range of rotation speeds and fluid application flow rates, the experimental data are seen to compare favorably with the model predictions.     

Investigation of atomization concepts for large‐scale flame spray pyrolysis (FSP)

Flame spray pyrolysis (FSP) is a versatile process for the production of inorganic nanoparticles featuring the advantage that the reagents are directly dissolved in the liquid fuel that is atomized to form the burning flame. A majority of previous studies on flame spray pyrolysis is focused on the formation and growth processes of the nanoparticles but neglect the preceding step of precursor atomization and spray formation. In this work an atomization concept for large‐scale nanoparticle production by flame spray pyrolysis is presented. A pressure swirl nozzle is applied for creating a liquid hollow cone, and in a second step, different dispersion gas nozzles are utilized to enhance the atomization of the liquid phase and to influence the spray cone formation and geometry. The relevant parameters influencing the atomization process (dispersion gas feed rate, liquid feed rate) are investigated (for air, water) in non‐burning (cold) spray conditions in order to access the utilization of the different atomizer concepts for the flame spray pyrolysis‐process. Measurements are conducted by applying high speed camera imaging (HSC), particle image velocimetry (PIV) and laser diffraction spectroscopy (LDS). Computational fluid dynamics (CFD) revealed further insight into the gas entrainment and the trajectory of droplets within the spray. Results show that the liquid volume flow rate (and thus the productivity of the process) may be increased significantly while still maintaining an appropriate droplet size compared to the conventional atomization process conditions in flame spray pyrolysis reactors.     

Generation of Aerosol Plasma in the Process of Volume Condensation in a Cloud of Surface Explosion Products

The paper deals with the process of formation of condensation aerosol and its effect on the concentration of electrons and negative and positive ions in a cloud of surface explosion products at the cooling stage. The subject of investigation is a heterogeneous mixture of vapors of mineral substances of soil, noncondensing gases (largely air), and unevaporated soil particles. A model is suggested of the process of volume condensation of soil vapors. The degree of effect of volume condensation on the concentration of electrons and ions was determined by comparing the electron concentrations calculated in view of and disregarding the thermal emission by aerosol droplets. It is found that a nonmonotonic temperature dependence of electron concentration with the presence of a minimum and a maximum is observed in the region of formation of condensation aerosol, as well as a significant (by several orders of magnitude) excess of the value of electron concentration over the value calculated disregarding the thermal emission. The low-temperature limit of this phenomenon is associated with the rapid increase in the concentration of negative molecular ions (mainly NO ₂ ^? ) at T < 1600 K.     

Effects of geometry and position of the metal delivery tube on ultrasonic gas atomization

The effects of the geometry and the position of the metal delivery tube on the pressure condition in the gas-metal interaction zone were studied. The measurements were performed under conditions which simulated ultrasonic gas atomization experiments, but at low gas atomization pressures (50–200 psig, 345–1380 kPa). Low gas atomization pressures are used in spray atomization and deposition processes such as liquid dynamic compaction (LDC), and Osprey. Depending on the experimental conditions, either underpressure or overpressure in the metal delivery tube was detected. The magnitude of the underpressures and overpressures was found to increase with the gas atomization pressure; the maximum pressure differences with respect to the atomization tank pressure were about 3 psi (21 kPa) when argon was used as an atomization gas with a pressure of 200 psig (1380 kPa). Underpressure or overpressure effects of such magnitude have a large effect on the metal flow rate during gas atomization. The large pressure differences measured in the present work result from using an atomizer with gas jet diameters larger than those used in previous investigations. Using a large ultrasonic atomizer, argon gas flow rates of about 5 kg/min can be obtained for atomization pressures of 200 psig (1380 kPa).     

Growth of the surface area of separated liquid fragments during high-temperature fragmentation of an inhomogeneous liquid drop

We have experimentally studied the formation of a droplet cloud during intense heating and subsequent explosive fragmentation of an inhomogeneous liquid drop. The experiments were performed with water drops containing graphite particles, which were heated in a flow of combustion products at a temperature varied from 600 to 1100 K. Three regimes of fragmentation of the inhomogeneous liquid drops have been observed, which are characterized by different total areas of liquid phase surface in aerosol clouds. Dependence of these regimes on the water/inclusion volume ratio and the amount of supplied heat has been determined.     

多层喷射共沉积制备 SiCP/Al-8.5Fe-1.3V-1.7Si复合材料

采用多层喷射沉积工艺制备SiC_P/Al-8.5Fe-1.3V-1.7Si复合材料, 研究了雾化及沉积工艺参数对沉积坯状态及SiC颗粒捕获的影响。结果表明, 液流直径大、雾化气体压力小、喷射高度小会导致沉积坯组织恶化, 反之则造成收得率低、致密度低。雾化器扫描不均匀则会造成沉积坯形状不均匀, 而且会由于热量集中导致显微组织恶化。SiC颗粒输送压力的提高有利于SiC颗粒的捕获以及颗粒的均匀分布。多层喷射沉积制备SiC_P/Al-8.5Fe-1.3V-1.7Si的优化工艺参数为: 液流直径3.6 mm, 雾化气体压力0.8 MPa, 喷射高度200 mm, SiC 颗粒输送压力0.5 MPa。 沉积坯存在两种SiC-Al界面: 晶态Si界面层与非晶态SiO₂界面层。     

Effect of model hydrometeors on the development of discharge from an artificial cloud of charged aqueous aerosol

The process of discharge initiation and propagation in clouds of a charged aqueous aerosol in the presence of coarse model hydrometeors has been experimentally studied. It is established that the development of a spark discharge in the gap between a charged aqueous aerosol cloud and a grounded plane depends on the parameters of hydrometeors, the site where a group of hydrometeors is situated, and the electric field strength. A group of conducting cylindrical model hydrometeors most effectively initiates a spark discharge between charged aqueous aerosol clouds. Optimum configurations of such a group for initiating and guiding a discharge are determined. Characteristics of the final stage of discharge from a charged aqueous aerosol cloud in the presence of model hydrometeors are analyzed.     

Multiply scattered aerosol lidar returns: inversion method and comparison with in situ measurements

A novel aerosol lidar inversion method based on the use of multiple-scattering contributions measured by a multiple-field-of-view receiver is proposed. The method requires assumptions that restrict applications to aerosol particles large enough to give rise to measurable multiple scattering and depends on parameters that must be specified empirically but that have an uncertainty range of much less than the boundary value and the backscatter-to-extinction ratio of the conventional single-scattering inversion methods. The proposed method is applied to cloud measurements. The solutions obtained are the profiles of the scattering coefficient and the effective diameter of the cloud droplets. With mild assumptions on the form of the function, the full-size distribution is estimated at each range position from which the extinction coefficient at any visible and infrared wavelength and the liquid water content can be determined. Typical results on slant-path-integrated optical depth, vertical extinction profiles, and fluctuation statistics are compared with in situ data obtained in two field experiments. The inversion works well in all cases reported here, i.e., for water clouds at optical depths between ~0.1 and ~4.     

Electrohydrodynamic atomization (EHDA) assisted wet chemical synthesis of nickel nanoparticles

In this study nickel nanoparticles were prepared via chemical reduction of nickel acetate using sodium borohydride using electrohydrodynamic atomization (EHDA) technique. This technique was used to spray a finely dispersed aerosol of nickel precursor solution into the reductive bath. Obtained particles were characterized by means of X-ray diffraction (XRD), UV–Visible spectroscopy, and transmission electron microscopy (TEM). Results confirmed the formation of nickel nanoparticles and showed that applying EHDA technique to chemical reduction method results in producing smaller particles with narrower size distribution in comparison with conventional reductive precipitation method.     

玉米淀粉粉尘爆炸特性及火焰传播过程的试验研究?

为了全面地认识玉米淀粉粉尘爆炸的敏感性和爆炸破坏效应,分别采用粉尘云着火温度装置、20 L球粉尘爆炸装置和粉尘云火焰传播装置对玉米淀粉的粉尘云着火温度、爆炸下限质量浓度、爆炸压力、爆炸氧极限浓度以及粉尘云火焰传播过程进行了研究。结果表明:玉米淀粉粉尘云最低着火温度在380~390℃之间;粉尘云爆炸氧极限浓度(体积分数)在10%~11%之间;爆炸下限质量浓度和最大爆炸压力随着化学点火具质量的增加而呈现出不同的变化特征,随着化学点火具质量的增加,玉米淀粉的爆炸下限质量浓度逐渐降低,而玉米淀粉爆炸压力逐渐升高。在不同的粉尘质量浓度条件下,粉尘云火焰传播速度和火焰温度有一定的变化,在粉尘质量浓度为500 g/m3时,火焰传播速度和火焰温度均达到最大值,分别为13.81 m/s和1 107℃。     

Understanding nanoparticle formation by a wire explosion process through experimental and modelling studies

A wire explosion process (WEP) has been used to produce nano aluminium powder in nitrogen, argon and helium atmospheres. The impact of energy deposited into the exploding conductor on the size and shape of the particles was analysed using TEM analysis, which forms the first part of the study. It is observed that the higher the energy deposited, the smaller the particles formed. In the second part, modelling studies were carried out by solving the general dynamic equation through the nodal approach, and the particle size distributions were predicted. It is realized that, at the point of high saturation ratio and nucleation rate, the size of the critical nucleus formed is low. The particle size distribution predicted by the model correlates well with the experimental results. Time-series analysis of particle formation indicates that particles of lower dimensions form and, in the process of coagulation, larger particles are formed. It is realized that the plasma formed during the explosion plays a major role in the particle formation, and the modelling studies confirm that particle formation is not an instantaneous process but requires a certain time period to form stable sizes and shapes.     

Developments in vapour cloud explosion blast modeling

TNT Equivalency methods are widely used for vapour cloud explosion blast modeling. Presently, however, other types of models are available which do not have the fundamental objections TNT Equivalency models have. TNO Multi-Energy method is increasingly accepted as a more reasonable alternative to be used as a simple and practical method. Computer codes based on computational fluid dynamics (CFD) like AutoReaGas, developed by TNO and Century Dynamics, could be used also in case a more rigorous analysis is required. Application of the Multi-Energy method requires knowledge of two parameters describing the explosion: a charge size and a charge strength. During the last years, research has led to an improved determination of the charge strength (i.e., the class number or source overpressure) to be chosen to apply the blast charts. A correlation has been derived relating the charge strength to a set of parameters describing the boundary conditions of the flammable cloud and the fuel in the cloud. A simple approach may not be satisfactory in all situations. The overpressure distribution inside a vapour cloud explosion is generally not homogeneous and the presence of obstructions causes directional blast propagation in the near field. A CFD approach, in which the actual situation is modeled, supplies case-specific results. An overview of the key aspects relevant to the application of the Multi-Energy method and CFD modeling is provided. Then the application of the two methods is demonstrated for an example problem involving the calculation of the explosion blast load on a structure at some distance from the explosion in an offshore platform complex.     

Aerosol counterflow two-jets unit for continuous measurement of the soluble fraction of atmospheric aerosols

A new type of aerosol collector employing a liquid at laboratory temperature for continuous sampling of atmospheric particles is described. The collector operates on the principle of a Venturi scrubber. Sampled air flows at high linear velocity through two Venturi nozzles "atomizing" the liquid to form two jets of a polydisperse aerosol of fine droplets situated against each other. Counterflow jets of droplets collide, and within this process, the aerosol particles are captured into dispersed liquid. Under optimum conditions (air flow rate of 5 L/min and water flow rate of 2 mL/min), aerosol particles down to 0.3 microm in diameter are quantitatively collected in the collector into deionized water while the collection efficiency of smaller particles decreases. There is very little loss of fine aerosol within the aerosol counterflow two-jets unit (ACTJU). Coupling of the aerosol collector with an annular diffusion denuder located upstream of the collector ensures an artifact-free sampling of atmospheric aerosols. Operation of the ACTJU in combination with on-line detection devices allows in situ automated analysis of water-soluble aerosol species (e.g., NO2-, NO3-)with high time resolution (as high as 1 s). Under the optimum conditions, the limit of detection for particulate nitrite and nitrate is 28 and 77 ng/m(3), respectively. The instrument is sufficiently rugged for its application at routine monitoring of aerosol composition in the real time.     

Rapid generation of protein aerosols and nanoparticles via surface acoustic wave atomization

We describe the fabrication of a surface acoustic wave (SAW) atomizer and show its ability to generate monodisperse aerosols and particles for drug delivery applications. In particular, we demonstrate the generation of insulin liquid aerosols for pulmonary delivery and solid protein nanoparticles for transdermal and gastrointestinal delivery routes using 20?MHz SAW devices. Insulin droplets around 3?μm were obtained, matching the optimum range for maximizing absorption in the alveolar region. A new approach is provided to explain these atomized droplet diameters by returning to fundamental physical analysis and considering viscous-capillary and inertial-capillary force balance rather than employing modifications to the Kelvin equation under the assumption of parametric forcing that has been extended to these frequencies in past investigations. In addition, we consider possible mechanisms by which the droplet ejections take place with the aid of high-speed flow visualization. Finally, we show that nanoscale protein particles (50-100?nm in diameter) were obtained through an evaporative process of the initial aerosol, the final size of which could be controlled merely by modifying the initial protein concentration. These results illustrate the feasibility of using SAW as a novel method for rapidly producing particles and droplets with a controlled and narrow size distribution.     

Granulation of ferrosilicon alloy by rotary multi-nozzles cup atomizer: Granulation behavior and model formation

Nowadays, ferroalloys are mainly produced by mold casting and crushing process in China which have obvious drawbacks like low efficiency and high energy consumption. In the present study, a novel process which was based on a rotary multi-nozzles cup atomizer (RMCA) was suggested on FeSi75 (alloy containing 75?wt.% Si). A circle of water curtain was set around the rotary multi-nozzles cup atomizer. According to the calculation results of atomization mechanism, the granulation process agreed with Rayleigh’s mechanism. During the breakup of the alloy ligament, the surface tension plays an important role on the formation of droplet, and the effect of centrifugal force on the diameter of the alloy droplets becomes obvious with the increasing of the rotating speed. In the current study, the models of the traveling trajectories and the heat transfer of the alloy droplet are established. It is found that the solidification time of droplet with different thickness of solidification layer increase with the increase the alloy droplets’ diameter. And the thickness of water curtain required for cooling the alloy increases with increasing the rotating speed.     

Mass Spectrometry of Liquid Aniline Aerosol Particles by IR/UV Laser Irradiation

The first results are reported from a new single-particle two-color laser time-of-flight mass spectrometer, incorporating a combination of infrared (CO(2)) and UV (excimer) laser irradiation. This combination of lasers has the capability to effectively separate the desorption or evaporation step from the ionization step, thereby greatly improving the analytical capabilities of such an instrument. The results on liquid aerosols, such as aniline, show that prior evaporation of the aerosol particle with the IR laser increases the ion signal produced by the excimer laser by more than 2 orders of magnitude. In the case of nitrobenzene aerosols, the excimer laser alone produces no ions, while a very large signal is observed when the aerosol is first irradiated with the CO(2) laser. A simple model, based on the Coulomb explosion of the ionized aerosol, is used to estimate the number of ions generated by the excimer laser (～10(5) ions). Experimental evidence based on the observed time delay of protonated aniline parent ions indicates that the laser irradiation of the liquid aerosol results in a stable neutral plasma which separates into positive and negative charges only after a 100-500-ns delay.