Effect of spray nozzle design on liquid-solid contact in fluidized beds

In industrial fluid cokers the feedstock, consisting of heavy bituminous hydrocarbons, is atomized with steam and injected into a hot fluidized bed of coke. Good and uniform contact of the liquid droplets with the solid particles is required to provide heat for the cracking reactions while minimizing mass transfer effects. Experiments in a pilot plant coker have suggested that the initial particle/liquid mixing, in the spray jet, is rather poor. Experiments in a X-ray scanner showed that liquid droplets and entrained particles accumulate just below the tip of the jet plume to form agglomerates.An experimental technique was used to quantitatively determine the quality of mixing with a variety of nozzle configurations including several novel designs. By improving spray stability, redistributing liquid droplets to the solids-rich region of the jet and increasing the surface area of the gas-liquid jet-fluidized bed interface, liquid/solid contact is improved.     

Atomization of metal fluorides for enhanced flow characteristics of a multicomponent powder

The National Aeronautics and Space Administration's (NASA's) PS304 coating is a plasma spray deposited tribological coating with feedstock composed of NiCr, Cr₂O₃, Ag and BaF₂-CaF₂ powders. The effects of rounded BaF₂-CaF₂ particles on the gravity-fed flow characteristics of PS304 feedstock have been investigated. The BaF₂-CaF₂ powder was fabricated by water atomization using four sets of process parameters. Each of these powders was then characterized by microscopy and classified by screening to obtain 45-106 μm particles and added incrementally from 0-10 wt.% to the other constituents of the PS304 feedstock, namely nichrome, chromia and silver powders. The relationship between feedstock flow rate, measured with the Hall flowmeter, and concentration of fluorides was found to be linear in each case. The slopes of the lines were between those of the linear relationships previously reported using angular and spherical fluorides and were closer to the relationship predicted using the rule of mixtures. The results offer a fluoride fabrication technique potentially more cost-effective than gas atomization processes or traditional comminution processes.     

雾化参数对H70黄铜粉末粒度及其分布的影响

气雾化生产金属粉末是一个复杂的过程,影响因素较多.为制备较细粉末需求最佳的工艺参数组合,应用气体动力学和流体力学分析了雾化气体压力、金属熔体温度和导液管内径对H70黄铜雾化粉末粒度及其分布的影响.结果表明:适当地提高气体压力和金属熔体温度或者减小导液管内径均能使雾化粉末粒度增大,当雾化气体压力为1.3 MPa,金属熔体温度为1 160 ℃时,导液管内径为3.5 mm时,所制得的粉末的粒度及其分布均达到最佳效果.     

Machinability enhancement of stir cast Al-TiCp composites under cryogenic condition

The current research work makes an attempt to develop a methodology in order to produce high-quality Al-TiC_p composites by using systemized inert atmospheric stir casting facility. The quality of produced composites was characterized using microstructural, Energy-dispersive X-ray spectroscopy (EDX), and machinability studies. Atomized-Cryogenic-Liquid (ACL) spray machining technique was developed and used to enhance the machinability of composite. The results of microstructural analysis reveal that TiC_p refines Al grain structure to 50 times lesser than non-reinforced Al grains along the full length of the casting. Energy-dispersive X-ray analysis confirms that no metallic reaction takes place. Machining studies reveal that atomized cryogenic liquid-spray machining significantly improves the quality of machined surface and reduces the progressive wear occurring on tool during turning of Al-TiC_p composites in comparison with cryogenically chilled argon, wet, and dry machining conditions, respectively. The scientific methodology highlighted in this study helps to improve the productivity and reduces the manufacturing cost in various industrial applications.     

Corrosion of Al—Fe in hydrochloric acid

Abstract

Nanoprocessing can be considered a distinct form of grain boundary engineering by which property enhancements are achieved by deliberately increasing the volume fractions of grain boundaries and triple junctions in a material. Electrodeposition has been shown to be a technologically viable production method to synthesize such materials both in bulk form and as thin films. The mechanical, magnetic, electrical and corrosion properties exhibited by nanocrystalline metals produced by this method make them strong contenders for a number of advanced materials applications.

Résumé

Nous pouvons considérer le nanotraitement comme une forme distincte de génie des joints de grains par lequel nous obtenons des améliorations de propriétés en augmentant délibérément le volume des fractions des joints de grains et des jonctions triples dans les matériaux. On a montré que l'électrodéposition est une méthode technologiquement viable pour synthétiser de tels matériaux, aussi bien en films minces que sous forme massive. Les propriétés mécaniques, magnétiques, électriques et corrosives des métaux nanocristallins obtenus par cette méthode, font d'eux des concurrents sérieux pour nombreuses applications de matériaux avancés.     

Experiments and modeling of discharge characteristics in water-mist sprays generated by pressure-swirl atomizers

Pressure-swirl atomizers are often employed to generate a water-mist spray,typically employed in fire suppression.In the present study,an experimental characterization of dispersion(velocity and cone angle)and atomization(drop-size axial evolution)was carried out following a previously developed methodology,with specific reference to the initial region of the spray.Laser-based techniques were used to quantitatively evaluate the considered phenomena:velocity field was reconstructed through a Particle Image Velocimetry analysis;drop-size distribution was measured by a Malvern Spraytec device,highlighting secondary atomization and subsequent coalescence along the spray axis.Moreover,a comprehensive set of relations was validated as predictive of the involved parameters,following an inviscid-fluid approach.The proposed model pertains to early studies on pressure-swirl atomizers and primarily yields to determine both initial velocity and cone angle.The spray thickness is also predicted and a classic correlation for Sauter Mean Diameter is shown to provide good agreement with experimental results.The analysis was carried out at the operative pressure of 80 bar;two injectors were employed featuring different orifice diameters and flow numbers,as a sort of parametric approach to this spray typology.     

重油催化裂化进料雾化喷嘴出口结构对喷嘴性能的影响研究

采用Fluent软件,基于欧拉-欧拉方法的VOF多相流模型对喷嘴的内部流场进行仿真分析,研究喷嘴出口段结构参数对喷嘴性能的影响;在确定喷嘴出口段最优结构的基础上,应用基于欧拉-拉格朗日方法的DPM模型对喷嘴的外部雾化射流区域进行了雾化状态分析,并探究了喷嘴的雾化机制.结果表明:出口锥角θ=51°时喷嘴的性能最优,平均速度为101.19 m/s,湍流强度为2141.1％,达到最大值;出口长度L2=20 mm时喷嘴的性能最优,速度为101.03 m/s,湍流强度为2121％;出口直径d2=25 mm时喷嘴性能最优,平均速度为101.49 m/s,湍流强度为2101％,且出口直径d2对喷嘴的雾化性能影响最大.并根据优化后的结构尺寸进行了5:1比例缩小的实验,对喷嘴内部液相流动状态呈四点分布进行了验证,同时喷嘴外部雾化液滴分布锥角与仿真结果误差为3.81％,雾化液滴粒径最大误差为3.67％.     

Spray drying with a two-fluid nozzle to produce fine particles: Atomization,scale-up,and modeling

This article presents experimental and modeling work to complete previously reported work on spray drying. Back-calculated droplet sizes have been verified by measurements with a laser imaging rig. Flow patterns in a cylindrical spray chamber have been simulated by computational fluid dynamics and demonstrated that droplet residence times are much shorter than expected. A droplet tracking population balance model has been implemented in gSOLIDS and shows how drying times vary with droplet diameter. Particle collection by cyclone and bag filter have also been compared experimentally.     

Microscopic and macroscopic atomization characteristics of a pressure-swirl atomizer,injecting a viscous fuel oil

Combustion of heavy fuels is one of the main sources of greenhouse gases, particulate emissions, ashes, NOxand SOx. Gasification is an advanced and environmentally friendly process that generates combustible and clean gas products such as hydrogen. Some entrained flow gasifiers operate with Heavy Fuel Oil(HFO) feedstock. In this application, HFO atomization is very important in determining the performance and efficiency of the gasifiers.The atomization characteristics of HFO(Mazut) discharging from a pressure-swirl atomizer(PSA) are studied for different pressures difference(Δp) and temperatures in the atmospheric ambient. The investigated parameters include atomizer mass flow rate( _m), discharge coefficient(CD), spray cone angle(θ), breakup length(Lb), the unstable wavelength of undulations on the liquid sheet(λs), global and local SMD(sauter mean diameter) and size distribution of droplets. The characteristics of Mazut sheet breakup are deduced from the shadowgraph technique. The experiments on Mazut film breakup were compared with the predictions obtained from the liquid film breakup model. Validity of the theory for predicting maximum unstable wavelength was investigated for HFO(as a highly viscous liquid). A modification on the formulation of maximum unstable wavelength was presented for HFO. SMD decreases by getting far from the atomizer. The measurement for SMD and θ were compared with the available correlations. The comparisons of the available correlations with the measurements of SMD andθ show a good agreement for Ballester and Varde correlations, respectively. The results show that the experimental sizing data could be presented by Rosin-Rammler distributions very well at different pressure difference and temperatures.     

采煤工作面局部风流雾化降温效果分析

为分析低温雾化喷淋对高温采煤工作面局部风流的降温效果,采用Eulerian-Lagrangian二相流描述方法,通过液滴与湿空气的双向耦合作用,对高温风流的降温效果进行了数值计算,计算结果表明：1次降温后,风流温度约有4℃的急剧降低,1排喷嘴的有效作用距离为10 m,10 m后,风流温度又逐渐升高1.5℃,总体上,回采面风流的温度呈现出阶跃性的上升趋势;拟合得到的风流降温效果随喷嘴流量呈负指数变化;液滴喷射角在70°~90°范围时,降温效果较明显,而细水雾的高压雾化喷嘴能明显提高降温效果。