射流携带床气化炉内宏观混合过程研究(Ⅰ) 冷态浓度分布

以双通道交叉射流喷嘴为射流源,在直径1000mm、高4000mm的大型冷模装置上,测定了射流携带床气化炉内的冷态浓度分布,考察了喷嘴环隙和中心射流动量比对宏观混合过程的影响;给出了无量纲径向浓度分布、无量纲最大浓度和混合分数的轴向衰减以及无量纲浓度半半径沿轴向的变化规律。     

单喷嘴气化炉内稠密气-固两相旋流浓度场研究

旋转射流在实际工程中应用广泛,利用PV6D颗粒测速仪测量了旋转射流气化炉内颗粒的浓度场特性。结果表明：加旋情况下,喷嘴轴线处的颗粒浓度较不加旋时衰减快,在气化炉上部的测量截面上,颗粒浓度的径向呈＂驼峰＂分布,而在气化炉下部则分布较均匀;随着固气质量比和颗粒粒径的减小,颗粒轴线的相对浓度衰减加快。     

一种新型自吸式喷嘴喷射性能初步研究

建立实验装置,研究一种带凸形圆环结构的新型自吸式气液二相喷嘴的吸气溶氧性能。以吸上真空度和溶解氧为目标,考察喷射口直径、凸形圆环缩颈直径与喷射口直径比、锥形喷射口与凸形圆环缩颈上端间距离等参数对喷嘴喷射性能的影响,并与普通喷嘴对比。结果表明:上述3个参数均能影响溶氧能力,而喷射口直径、凸形圆环缩颈直径与喷射口直径比则主要影响吸上真空度;相同液体流量下,新型喷嘴吸上真空度和溶氧能力均好于普通喷嘴;较优的结构参数是喷射口直径D、凸形圆环缩颈直径与喷射口直径比为1.2、锥形喷射口与凸形圆环缩颈上端间距离则为4D。     

Simultaneous numerical simulation of nano and fine particle coagulation and dispersion in a round jet

The discrete vortex method coupled with the particle-tracking and moment methods have been used to calculate the trajectories of individual nano and fine particles undergoing the coagulation and dispersion in a round jet. The results show that the Stokes number plays an important role in the dispersion of fine particles. The radial dispersion of fine particles for the wavenumber of 5 is the largest when an azimuthal perturbation is introduced to its flow. However, the width of particle dispersion is not always proportional to the amplitude of the azimuthal perturbation. As the round jet flow develops, the mass concentration of nanoparticles within the jet core decreases continuously. The number concentration of nanoparticle decreases rapidly near the jet exit, then decreases slowly in the far field until an asymptotic state is attained. Both the polydispersity and diameter of nanoparticle increase, the rate of increase for the former is the largest near the jet exit, and the largest particles are found near the jet core. The particle diameter is relatively constant across the width of the jet within and outside the jet core except the region near the interface of the jet and the outside. The standard deviation of nanoparticle size distribution increases at the jet exit, approaching slowly at an asymptotic value in the jet core. The minimum and maximum of standard deviation appear between the jet core and edge, and at the jet centerline, respectively. The region of mixing of nanoparticles becomes narrower, however, the particle number concentration grows with increasing Schmidt number. The particle size increases along the radial direction with increasing Damkohler number, and the standard deviation does not change when the Damkohler number is monotonous.     

射流混合器内气体湍流扩散过程的CFD数值模拟与实验研究

利用计算流体动力学CFD(Computational Fluid Dynamics)商业软件CFX4.4对二氧化碳与空气的射流混合过程进行数值模拟. 湍流模型采用标准k-e模型和RNG模型,模拟预测不同断面上的CO2浓度分布,并与实验结果进行比较. 结果表明,模拟预测值与实验结果基本吻合,也验证了CFD技术应用于混合扩散过程预测分析的可靠性;靠近空气一侧的CO2浓度普遍高于另一侧,当CO2平均浓度为6%时,距射流出口100 mm剖面上的浓度极差达到6%. 本研究中的气体混合湍流模型影响不明显. 采用标准k-e模型分别对两种进气方式的射流混合器内部速度场、浓度场进行模拟分析,发现T型射流混合器的混合均匀性比单边进气的射流混合器明显提高.     

Experimental investigation on flow structures and mixing mechanisms of a gas–solid burner jet

The objective of this study was to investigate the flow structures and mixing mechanisms of a gas–solid two-phase jet from a burner employed in the utility boiler. Laboratory experiments were conducted in a 0.15 m internal diameter test facility. Gas–solid jet flow downstream of the burner exit was measured by a fiber optic probe. Local solid concentration and particle size distribution were obtained using the probe that was traversed over the cross-section of the jet. The effects of the side flow on the primary air gas–solid flow characteristics were also studied. The measurements showed the availability of fiber optic probe to investigate the gas–solid jet flow downstream the industrial burner nozzle with high solid concentration. Obvious slip between the gas phase and the solid phase in the gas–solid jet flow was found in the experiments. The side flow disturbed the solid concentration distribution in the jet, a more smooth solid concentration profile across the jet can be achieved after the side flow was introduced. The particle size distributions in the jet were similar with the distributions of the solid concentration, the particles with large diameters always appeared in the zones where the solid concentrations were high.     

Jet evolution and fiber formation mechanism of amylopectin rich starches in centrifugal spinning system

This article reports the jet evolution process and fiber formation mechanism of the amylopectin rich starch solution in centrifugal spinning system, and the linear polyvinylpyrrolidone (PVP) is applied to compare with starch solution. The results indicate that jet evolution processes of starch solution include steady state and Rayleigh–Taylor instability over the whole concentration range for the spinnability investigation, which are due to the hyperbranched molecular of amylopectin. As a compression, the linear molecular chain PVP solution expresses a steady state jet under the spinning concentration. The spinnability results show that the obtained starch fibers are always containing the beads due to the Rayleigh–Taylor instability of jet, but can be effectively controlled by solution concentration and amylose/amylopectin. Instead, the PVP fibers show a rapid decreasing of beads till to almost disappear with the increasing of solution concentration, which due to the improvement of chain entanglement increase the steady state portion of jet with the increasing of concentration. The thermal properties of obtained fiber show that fibers obtained from amylose with more thermal stability.     

新型催化裂化提升管进料段内原料射流浓度分布的大型冷模实验研究

通过大型冷模实验研究了喷嘴射流与催化剂逆向接触的新型提升管进料段内喷嘴射流浓度沿径向的分布,考察了喷嘴气速、预提升气速的影响. 结果表明,喷嘴气速Uj=78.5 m/s和预提升气速Ur=4.1 m/s条件下可获得较好的油剂混合效果. 与传统形式相比,新型结构可促进油剂混合,在轴向距离H<0.7 m内完成油剂混合,油剂初始接触区域内喷嘴射流相浓度分布更均匀. 给出了新型进料段中不同区域喷嘴射流浓度沿径向分布的经验模型,计算值与实验值吻合较好.     

High-speed jet electrodeposition and microstructure of nanocrystalline Ni-Co alloys

The jet electrodeposition from watts baths with a device of electrolyte jet was carried out to prepare nano-crystalline cobalt-nickel alloys. The influence of the concentration of Co²⁺ ions in the electrolyte and electrolysis parameters, such as the cathodic current density, the temperature as well as the electrolyte jet speed, on the chemistry and microstructure of Ni-Co-deposit alloys were investigated. Experimental results indicated that increasing the Co²⁺ ions concentration in the bath, the electrolyte jet speed and decreasing of the cathodic current density and decrease of the electrolyte temperature all results in an increase of cobalt content in the alloy. Detailed microstructure changes upon the changes of alloy composition and experimental conditions were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD results show the Ni-Co solid solution was formed through the jet electrodeposition. Phase constitution of solid solution changes progressively under different electrolyte concentration. Alloys with low Co concentration exhibit single phase of face-centered cubic (fcc) structure; The Co concentration over 60.39 wt.%, the alloys are composed of face-centered cubic (fcc) phase and hexagonal close-packed (hcp) phase. Furthermore, the formation of the nanostructured Ni-Co alloy deposit is investigated. Increasing the Co²⁺ ions concentration in the bath, the cathodic current density, the electrolyte temperature and the electrolyte jet speed all result in the finer grains in the deposits. Additives such as saccharin in the electrolyte also favor the formation of the finer grains in the alloy deposits.     

Mixing indices in coflowing plane jets: High momentum conditions

Mixing indices describing the completeness of mixing between pairs of plane jets in a triple coflowing jet array have been measured using marker nephelometry. This work is an extension of the results reported by Grandmaison and Zettler (1989) for the case where the centre jet in the array has a higher velocity than the adjacent outer jets. Results include centreline measurements of the static pressure, mean velocity and mean and fluctuation concentration fields, as well as transverse measurements of these properties and concentration intermittency in the near field region where there is significant mixing between the jet streams.     

The falling laminar jet of semi-dilute polymer solutions

The studies of falling laminar jets have been done mainly on Newtonian jet due to the complexity of non-Newtonian fluid parameter. Numerical solutions of the Newtonian jet equation are in good agreement with the experimental results of polymer solutions in the experimental concentration range. Numerical simulation results suggest that the free falling jet is mostly influenced by the Froude number. The jet radius increases with the Froude number. It was found that surface tension or viscosity does not contribute much to the shapes of the free falling jet.     

氢气泄漏过程的理论模型计算及CFD模拟

采用Fluent数值模型虽然可以较为准确地预测氢气泄漏后的扩散和运动规律,但是建模及计算时间较长。提出一种新型理论模型,可以在很短时间内预测氢气泄漏的扩散和运动规律,适用于应急处理。为了探究理论模型的准确性,还建立了二维和三维的CFD模型进行计算。对不同尺寸泄漏口的水平和竖直方向的两种射流进行了研究,计算了氢气泄漏时射流轮廓及摩尔分数分布,预测了基于可燃极限计算的储罐周围的安全区域。比较了氢气射流的理论模型和CFD模型计算结果,并且与前人的实验结果做了比较,吻合度很好。研究还发现Froude数较高的射流是动量控制的射流;而较低情况下有射流很强的浮升力效应,氢气的摩尔分数下降速率加快。     

三维凹壁面切向射流流动特性分析

在立式圆筒体分层器内设置半圆形截面切向入口，形成三维凹壁面切向射流，以提高非均相物料机械分离效率。为了揭示三维凹壁面切向射流流动机理，利用示踪剂浓度实验和大涡模拟研究了凹壁面切向射流流动特性，并对浓度场沿流向和展向扩展进行了评价。研究结果表明，示踪剂浓度半值宽随着入口Reynolds数的提高扩展范围增加，流向扩展率为0.019～0.033，展向扩展率为0.079～0.161。在离心力作用下，入口周向60°范围内浓度半值宽沿流向收缩至射流宽度的2/3。圆筒体内壁面存在多个周向滚动发展的流向涡旋，但无展向涡旋。切向速度半值宽和涡量边界值在流向涡旋中心位置出现峰值，展向无明显波动。入口周向180°范围内，未发现二次流涡旋，沿射流流向的切向速度半值宽与圆筒体半径之比小于0.1，未达到离心不稳定性二次流的形成条件。凹壁面切向射流有效降低了涡旋对分层器内主流体的扰动。     

表面张力变化对含气泡液体射流破裂的影响

使用高速相机研究了表面张力变化对含气泡液体射流破裂过程的影响。通过改变表面活性剂浓度获得了不同表面张力的液体射流。实验发现当液体射流速度保持不变时,减小液体表面张力会增加射流破裂长度。表面活性剂一方面降低了液体动态表面张力,减小了射流表面不稳定波的增长率,增大了射流破裂长度;另一方面表面活性剂在射流表面的非均匀分布会产生Marangoni应力,促使液体向射流变形区运动,从而推迟了射流破裂的发生,增大了射流破裂长度。通过理论分析得到了液体射流破裂长度表达式。发现射流内部气泡会显著缩短含表面活性剂射流的破裂长度。通过气泡扰动射流速度和吸附表面活性剂的分析,揭示了内部气泡对含表面活性剂射流破裂的影响规律。     

Turbulent mixing in coflowing plane jets

The scalar mixing field of a single plane jet and an array of three coflowing plane jets has been examined using marker nephelometry. Results are reported for the centreline behaviour of the mean and fluctuation concentration fields of the single jet and the triple jet array with G_i/G_o = 1.39, 0.222 and 0.089, where G_i is the centre jet momentum and G_o the momentum of both outer jets. Details of the flow scales including the half concentration width and integral scales are also reported for the single plane jet and the triple jet case with G_i/G_o = 1.39 and 0.089. The centreline measurements were extended to the region where a tendency to axisymmetric behaviour was observed.     

基于可见蒸汽云对LNG喷射泄漏爆炸下限区域的预测

喷射泄漏在LNG泄漏事故中比较常见,由于其蒸汽本身无色无味,难从感观上判断其泄漏扩散范围。但由于其温度低,喷射泄漏会使周边环境空气中水蒸气液化成可见蒸汽云。通过建立LNG喷射泄漏计算流体力学模型,对不同环境条件和喷射速度下的扩散情形进行数值模拟,得到了LNG泄漏扩散区域的温度场和浓度场。根据环境条件和温度场分布,得到了可见蒸汽云区域范围,并总结出可见蒸汽云区域范围与爆炸下限区域范围的关系。喷射泄漏发生时,可以为预测爆炸下限区域范围,划定安全隔离范围和消防救援提供帮助。     

EXPERIMENTAL AND NUMERICAL STUDY ON GAS FLOW IN THE GRID ZONE OF JETTING-FLUIDIZED BEDS

A grid model describing the gas flow and interchange in the grid zone of jetting fluidized beds is proposed. Based on this model, longitudinal gas concentration profiles in the jet and annulus are calculated. The longitudinal gas concentration distribution is also experimentally investigated in a jetting fluidized bed with an inside diameter of 50 mm at the ambient temperature, and a jetting fluidized bed with an inside diameter of 80 mm at high temperatures. Comparison between the calculated and experimental results has shown that the experimental profiles can be qualitatively predicted by the grid model. The results indicated that the concentration in the grid zone depends on the gas exchange between the jet and the annulus, and the net gas flow from the jet to the annulus. The gas exchange rate is mainly affected by the inlet gas velocity from the nozzle. The present study is thought to be helpful to understand the grid gas behavior in the jetting fluidized bed coal gasifier.     

The distribution of sulfur compounds in hydrotreated jet fuels: Implications for obtaining low-sulfur petroleum fractions

The mechanism by which jet fuels are hydrotreated to reduce sulfur levels has some important implications in terms of the species and distribution of sulfur compounds remaining in the fuel. The species of sulfur that are most difficult to remove by hydrotreating, such as benzothiophenes and methyl- and dimethyl-benzothiophenes, are concentrated in the higher-boiling fraction of the fuel. Consequently, the lower-boiling fractions of the fuel contain much less sulfur. It may be possible, therefore, to obtain petroleum fractions that contain low levels of sulfur simply by distillation of the jet fuel into low-boiling and high-boiling fractions. A multi-element simulated distillation procedure according to ASTM D-2887, standard test method for boiling range distribution of petroleum fractions by gas chromatography, was coupled with atomic emission detection (GC-AED) and was used to estimate the sulfur concentration in various fractions of jet fuel, namely 20, 50, and 60%. The estimations of sulfur concentration were verified by comparing them to analyzed sulfur concentrations in several fractions of physical distillations of the jet fuels according to a modified ASTM D-86, standard test method for distillation of petroleum products at atmospheric pressure. Sulfur analyses showed that for all fuels analyzed, the initial 20% boiling fraction of the fuel contained no more than approximately 5% of the total sulfur concentration. The initial 50% boiling fraction of the fuel contained no more than 25% of the total sulfur concentration, and in most cases contained significantly less (8-16%). The total concentration of sulfur in the jet fuels tested ranged from 260 to 1380 μg/g, and there did not appear to be a direct relationship between total sulfur concentration and percentage of sulfur in each jet fuel boiling fraction.     

Flame structure of LPG-air Inverse Diffusion Flame in a backstep burner

The present experimental study characterizes the turbulent LPG Inverse Diffusion Flame (IDF) stabilized in a backstep burner in terms of visible flame length, dual flame structure, centerline temperature distribution, and oxygen concentration. The visible flame length for a fixed fuel jet velocity is found to reduce with increase in air jet velocity. Besides this, the effect of air and fuel jet velocities on visible flame length is interpreted using a new parameter, Global Momentum Ratio (GMR). Interestingly, GMR seems to be correlating well with the visible flame length for the air and fuel velocity ranges considered in the present study. Moreover, the dual flame structure of IDF is identified with the help of CH-chemiluminescence signature. The existence of dual flame structure of IDF is confirmed further with the centerline temperature and oxygen concentration measurements.