大空间液氢射流泄漏扩散特性

建立了大空间液氢射流泄漏三维非稳态CFD数值计算模型,开展了泄漏扩散规律研究。并对比研究了静风与顺风条件下,液氢射流泄漏所产生氢气云团的运动特性,使用无量纲数对同一时刻流场中不同位置的氢气云团行为进行了分析。结果表明,液氢射流泄漏过程包括自由出流、相变沉降、气云上升和稳定四个阶段。射流体具有较大水平速度时,由于惯性力的作用更显著,浮升力的作用难以体现,氢气云团会贴地运动更长的距离,这也增大了泄漏事故的危害性。     

高压氢气泄漏射流研究进展

叙述了高压氢气泄漏射流研究进展，重点对氢气状态方程、欠膨胀射流结构及模型、射流区域氢气浓度预测、基于计算流体动力学的泄漏射流模拟等方面进行了归纳、总结和评述，并对未来研究方向进行了展望。文中总结：现有研究表明已有多种适用于高压氢气的实际状态方程，Peng-Robinson、Abel-Noble等方程兼具便捷性及精度；高压氢气泄漏时在泄漏口呈现高度欠膨胀射流结构，Molkov模型可用于预测欠膨胀射流特性参数；高压氢气泄漏射流区为动量控制或动量与浮力联合控制，区域内氢气浓度与泄漏口径、泄漏口距离、介质密度组成的量纲为1参数有量化关系；主流计算流体动力学软件如ANSYS-Fluent、FLACS等在模拟高压氢气泄漏时均被证实具有较好精度。未来研究方向包括大尺度实验、不规则泄漏口、成果工程化应用以及高效数值模拟方法等。     

高压储氢罐不同位置泄漏扩散的数值模拟研究

随着氢能广泛的应用,储氢容器将日益增多,泄漏破坏等事故将不可避免.今建立了高压储氢罐泄漏扩散的模型,提出了研究高压储氢罐泄漏扩散的数值模拟方法.通过对高压储氢罐不同位置发生泄漏扩散的数值计算,得到了不同位置泄漏后的扩散特性.对比数值模拟结果,认为储氢罐侧面与底面位置发生泄漏时,其危险性要远大于储罐顶部发生泄漏.通过数值分析,得出了该模拟条件下的危险区域在射流方向的传输距离与时间的近似关系公式.数值模拟结果可以为加氢站等场所处理氢气泄漏事故提供参考.     

城市建筑环境下燃气泄漏扩散的数值模拟

为分析泄漏时间、管道压力、泄漏口与建筑物距离三个因素对街道天然气管道泄漏的影响,采用计算流体力学的方法对天然气管道泄漏扩散进行模拟,得到不同影响因素下的甲烷体积分数分布。研究表明:随着泄漏时间的增加,射流高度的增加,气体射流速度逐渐减小,甲烷逐渐向四周扩散;泄漏压力对泄漏的影响较大,直接影响扩散范围;建筑物对甲烷体积分数分布和变化产生很大影响,泄漏天然气对旁边的建筑物有贴附效应。     

化工企业实验室氢气泄露模拟分析

基于计算流体力学对化工企业实验室氢气泄露进行模拟,研究了泄露速度和通风口直径对氢气泄露扩散的影响。结果表明:实验室氢气泄露以射流初始扩散,泄露过程中上浮扩散,空间内形成旋涡,泄漏源附近室顶区域属于最危险区域,氢气泄露速度越快,泄漏口直径越大,其在实验室区域内扩散越快,危险程度越高。     

不同水流速度对海底管道油品泄漏的影响

为了预测海底管道泄露油品的扩散规律,解决油品泄露后的回收处理问题。基于计算流体力学CFD的基础,选取k-ε模型和VOF模型建立数值模拟仿真模型,根据不同的水流速度,模拟了原油泄露后的扩散情况。不同的水流速度扩散可以分为三个阶段:第一阶段,水流速度较低时,射流持续时间短,发生位置较高横向扩散位移呈线性变化。第二阶段水流速度变大时,射流时间变长,扩散的横向位移基本满足线性变化但中间有一个短暂的缓变期。第三阶段,水流速度较大时,射流发生位置较低,油品泄露的横向位移先是扩散较慢之后扩散明显加速。该研究可为海底管道漏油应急预报系统提供理论参考。     

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.     

甲烷罐区泄漏的数值分析

采用CFD计算软件FLUENT在不同条件下对甲烷泄漏扩散过程进行模拟,以确定甲烷泄漏过程中的形态和预防机制,研究分析气体泄漏扩散后浓度的分布,并对模拟结果进行分析讨论,总结气体泄漏扩散的一般规律。     

高含硫天然气管道泄漏数值模拟

高含硫天然气管道经长期的内外腐蚀,经常发生泄漏事故.为了减少和降低天然气管道泄漏事故对人的危害,对甲烷及硫化氢的扩散规律进行研究日趋重要.利用计算流体力学的方法,采用仿真软件对高含硫天然气架空及埋地管道穿孔泄漏后的甲烷、硫化氢气体的扩散进行了数值模拟.架空管道泄漏初期为体积分数等值线呈对称分布的射流,泄漏至60s后无爆...     

危险液化气体瞬时泄漏扩散数值模拟研究进展

危险液化气体瞬时泄漏事故是化工工业中重大潜在灾害,急速爆炸会产生急速膨胀的二相蒸气云,因此事故本身既有对化工设备造成的物理爆炸危害,同时也会导致危险介质的扩散。文中概述了化工设备瞬时爆炸事故研究的历程,综述了计算流体力学技术(CFD)在预测液化气体瞬时泄漏事故后果中的应用,指出CFD技术虽然涉及的物理模型非常复杂,计算量较大,但模拟结果可以涵盖流场中包括微观液滴群的大量介质信息,可为节约研究成本和理论发展提供了可靠的研究工具。文中还对事故研究发展和CFD模拟技术应用模式前景提出了展望。     

Twin jets in cross-flow

An experimental study and numerical investigation of thermal mixing are carried out on tandem twin jets in cross flow. Experiments were carried out for velocity ratios 1, 2 and 4 for 15 °C temperature difference between main pipe and jet fluid. Velocity and temperature fields are measured using Hot Film Anemometer (HFA). Three dimensional steady state Computational Fluid Dynamics (CFD) simulations have been carried out to predict the velocity and temperature fields. The predicted velocity and temperature fields are in good agreement with the experimental measurements. Temperature fluctuations have been predicted using temperature variance model. The effect of jet spacing for different velocity ratios is studied. For jet spacing equal to twice the jet diameter, both the jets influence each other. Increase in the jet spacing decreases the effect of jets on each other.     

多孔错流喷射混合器内液体射流轨迹线

利用平面激光诱导荧光测试技术对多孔错流喷射混合器内液体混合过程进行了研究,考察了操作条件（射流速度比r、混合流股Reynolds数Re_M）和混合器的结构参数（射流小孔直径d、孔径管径比d/D、射流小孔个数n）对射流轨迹线的影响。结果表明,混合流股Reynolds数对射流轨迹线影响较小,射流速度比和混合器的结构参数是影响射流轨迹线的主要因素。建立了射流轨迹线的数学模型,并利用实验结果回归了模型参数。模型预测的液体混合过程射流轨迹线与实验结果基本吻合。     

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。     

Three-dimensional vortex simulation for particulate jet generated by free falling particles

The particulate jet generated by solid particles falling from a circular orifice into an unbounded quiescent air is simulated. The three-dimensional vortex method, proposed for the analysis of particle-laden free turbulent flow in a prior study, is employed for the simulation. It is found that the falling particles induce complicated three-dimensional unsteady air flow involving large-scale eddies. The air takes its maximum velocity at the jet centerline, and the velocity profile satisfies the self-similarity around the centerline. The effect of particle diameter on the velocity distribution for the two phases is investigated. The entrained air flow rate is favorably compared with the value predicted by the analytical models.     

Theory and kinematic measurements of the mechanics of stable electrospun polymer jets

We present a simplified approach to understanding the mechanics of stable electrospinning jets based on electrohydrodynamic theory that explicitly incorporates the extensional rheology of polymeric fluids. Flow regimes of electrospun jets are identified by analogy to uniaxial extension of a fluid jet. These flow regimes predict the limiting kinematics of electrospinning jets and identify dimensionless parameters important to the control and operation of electrospinning processes. In situ kinematic measurements validate model assumptions and scaling predictions, and allow the reduction of entire jet radius and velocity profiles to several key parameters. The model predictions are shown to hold both above and below the entanglement concentration, as well as for solutions with added electrolyte and increased conductivity. The analysis also enables direct measurement of the apparent extensional viscosity of solutions at the high extension rates experienced during electrospinning. Finally, dimensional analysis of the model yields a correlation for electrospun fiber diameter in terms of measurable fluid properties, controlled process parameters, and measured jet variables, demonstrating the influence of mechanics in the straight portion of the jet on ultimate fiber morphology.     

基于XCT的气固流化床布风板射流特征研究

构建了X光层析成像（XCT）气固流动参数测量系统,基于锥形束滤波反投影算法（FDK）开发了CT三维重建软件,并设计了射流识别及量化算法。基于以上方法获得了不同流化风速下床料粒径d_p、布风板孔口直径d₀和布风板孔口均分面积A₀对射流形态结构和几何特征的影响规律。结果表明平均射流长度L、最大直径D和体积V与床料粒径d_p成反比,与孔口直径d₀和孔口均分面积A₀成正比,最终拟合了流化床平均射流长度关联式。     

Numerical analysis of particulate jet generated by free falling particles

This paper is concerned with the numerical simulation of the particulate jet generated by solid particles falling from a slit orifice into an unbounded quiescent air. A two-dimensional vortex method, proposed for the analysis of particle-laden free turbulent flow in prior papers, is employed for the simulation. The falling particles induce complicated air flow involving eddies with a wide variety of scales. The air takes its maximum velocity at the jet centerline. The particle velocity is higher than the free falling velocity of a single particle. The effects of the diameter and density of the particle on the flow are investigated. The entrained air flow rate is favorably compared with the value predicted by an analytical model.     

CFD simulation of flow pattern and plume dimensions in submerged condensation and reactive gas jets into a liquid bath

Submerged gas jets into a liquid bath are widely used in metal processing and thermal processes. These systems are classified as (a) condensation jet and (b) reaction jet systems. This paper presents the CFD simulation of both the types of jets. The CFD model considers phase change, gas-liquid and gas-gas reactions and the accompanied rates of mass transfer. Mass transfer coefficient was estimated using small eddy model where the value of mass transfer coefficient is calculated based on the local values of turbulent kinetic energy (k) and the dissipation rate (ε). A good agreement with the available experimental data of plume length validates the CFD model. The CFD simulations have also been compared with the available experimental data on velocity and temperature profiles which shows excellent agreement. A comparison between the condensation and the reaction jets has been presented in terms of plume dimensions, flow and temperature patterns. The relative predictions of the present model and the rational correlations have been presented for the estimation of plume length for both the types of jet systems.     

小间距两喷嘴对置撞击流流场的数值模拟与实验研究

运用热线风速仪和CFD软件对小喷嘴间距下两喷嘴对置撞击流时均流场进行了实验研究和数值模拟，并和文献中的实验结果和近似解析式进行了比较。研究结果表明：由于边界层存在，单股喷嘴出口速度分布为“礼帽”形状分布；在L<2D(L为喷嘴间距，D为喷嘴直径)时，喷嘴出口速度剖面出现中间低、两边高的“双峰”形状， L=2D时，“双峰”形状消失。随着喷嘴间距的增大，相同气速比导致的撞击面驻点的偏移量增大。相同气速比下，喷嘴出口为“礼帽”分布时驻点的偏移量比均匀分布时大。文献中的撞击流流场的近似解析式对喷嘴出口速度分布为均匀分布有很好的精度，当喷嘴出口速度为“礼帽”分布时，文献中近似解析式的预报精度变差。     

Effect of nozzle diameter and its orientation on the flow pattern and plume dimensions in gas-liquid jet reactors

Gas-liquid jet reactors are widely used in chemical industries in various applications such as feed-water heaters, metal processing, and thermal energy sources, etc. In all these applications, the principal requirement for the design is a prior knowledge of jet shape and dimensions, which primarily depend upon the nozzle type, size, submergence and its orientation. In the present study, CFD simulations of non-reacting (steam-water) and reacting (SF₆-Li) jets have been carried out to understand the variation in plume dimensions of gas-liquid jet reactors. For condensation jet and reaction jet, the criteria have been developed to identify the plume boundary based on the hold-up profile of steam/SF₆ gas and the evaporated fuel. The effect of nozzle diameter and its orientation, nozzle gas velocity and bath temperature on the plume dimensions have been studied for both the types of jets. It was observed that the extent of increase in the plume length is always higher in the case of reaction jet as compared to the condensation jet for all the cases. The analyses also proved that, the availability of reactant is much better with the horizontal orientation which leads to stable plume length. The CFD model has been extended for the prediction of the flow pattern and its effect on the rate of condensation/reaction and plume dimensions for both the jet systems.