共查询到20条相似文献,搜索用时 140 毫秒
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《化学反应工程与工艺》2018,(4)
以粒子图像流场测量(PIV)与计算流体力学(CFD)数值模拟相结合的方法,对气相和气固两相同轴射流流场特性进行了研究,探究了射流速度比、喷嘴直径、射流空间直径和射流出口直径对回流量和回流区域的影响规律。结果表明:射流区和壁面之间存在沿轴向延伸至整个射流长度的回流区域,中等Stokes数颗粒会随回流气体改变运动轨迹,聚集在低涡量高应变的回流涡点;射流速度比、喷嘴直径和射流空间直径对回流量影响显著,实验工况下的最大回流量是射流量的10.29倍;当射流充分发展后,射流出口直径对回流量没有影响。通过气固两相同轴射流流场特性的研究,为进一步阐明气固耦合的颗粒弥散机理提供了理论指导。 相似文献
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为了强化气固射流反应器内颗粒弥散和气固混合性能,采用光纤探针对不同喷嘴收缩射流颗粒浓度分布规律及其发展特性进行了研究;考察了射流速度和颗粒负载率对颗粒浓度分布、质量、动量和回流通量的影响。结果表明,喷嘴收缩效应使颗粒向射流轴线汇聚形成局部浓相区,收缩角的增大使浓相区向喷嘴靠近。回流卷吸和壁面效应的共同作用使颗粒浓度沿径向呈“多段式”分布特征。颗粒在射流轴线的汇聚和边壁区的富集降低了颗粒分布的均匀性。在射流近场,颗粒的质量和动量通量主要发生在射流剪切层;随剪切层的发展其通量峰值向边壁移动,而近壁区的颗粒回流使质量和动量通量显著增加。 相似文献
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介绍了FJC系列煤用喷射式浮选机核心部件充气搅拌装置的结构特点及工作原理;利用射流理论分析了充气搅拌装置内流体状态,并通过粒子图像测速(PIV)试验,分析了喉管内流体的速度矢量分布和涡量分布情况,证明充气搅拌装置内流体运动符合有限空间射流运动,同时还存在回流区,致使喉管内能量损失严重。 相似文献
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为了研究固定床熔渣气化炉喷嘴射流速度和安装角度对炉内流场的影响,搭建了固定床熔渣气化炉冷态试验平台,并结合Fluent软件进行了建模。结果发现:(1)随着气体流量和射流速度的不断增加,气体在物料内部的穿透距离不断加长;(2)随着喷嘴下倾角度的增加,射流深度、回流区径向深度及回流区高度呈不断减小趋势;当喷嘴下倾5°~10°布置时为最优工况,料层内部喷嘴方向射流穿透深度适中,炉内流场分布较好;(3)随着喷嘴切圆角度的不断增大,喷嘴对冲碰撞作用越小,气流逐渐偏离径向区域,喷嘴轴截面气体分布量逐渐变少,料层内部射流穿透深度先增大后减小。综合考虑各因素,喷嘴下倾5°并切圆旋转10°布置时,料层内部水平方向射流穿透深度最大,炉内流场分布较好。 相似文献
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介绍了FJC系列煤用喷射式浮选机核心部件充气搅拌装置的结构特点及工作原理;利用射流理论分析了充气搅拌装置内流体状态,并通过粒子图像测速(PIV)试验,分析了喉管内流体的速度矢量分布和涡量分布情况,证明充气搅拌装置内流体运动符合有限空间射流运动,同时还存在回流区,致使喉管内能量损失严重。 相似文献
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Previous experimental work shows that velocity ratio is the principal independent variable to determine the flow behavior of coaxial jets. This study focusing on the effect of velocity ratio on the flow characteristics such as the velocity and kinetic energy profiles, centerline velocity decaying, flow growing and entraining of the jet, presents a detailed numerical simulation of a coaxial jet with a secondary parallel moving stream. It is found that radial profiles of the mean velocity component u depending on the velocity ratio show good similarity in the fully developed zone. Compared with available experimental data, the results show that the use of standard κ-ε model leads to good agreement between the numerical results and experimental data. 相似文献
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The scalar mixing field of a free, turbulent concentric round jet has been examined using marker nephelometry. The flow conditions included velocity ratios between the centre and annular jet of 0.188, 0.519 and 0.911. The correlation function between the concentration fluctuations in the two jet streams increased from –1.0 near the nozzle to + 1.0 further downstream indicating a tendency to complete mixing between the jets. The initial mixing behaviour between the jets was better for the lower velocity ratio between the jets (Ui/Uo = 0.188) although further downstream there was better transverse mixing between the jets with the higher velocity ratio (Ui/Uo = 0.911). 相似文献
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Andrzej K. Bi 《Chemical Engineering Communications》1995,133(1):145-181
A theoretical and experimental analysis of mass transfer into a turbulent free liquid surface effected by submerged jets has been presented. Theoretical considerations concentrated on hydrodynamic characteristics of the system which enabled us to derive the radial velocity distribution in the surface jet flow. Some conclusions have been drawn from the two-parameter models of turbulence. The results of experimental measurements of the average mass transfer coefficients have been interpreted in terms of our own model of mass transfer accounting for eddy diffusivity. The model parameters were correlated with the basic hydrodynamic parameters of the system. Radial distributions of the local values of the mass transfer coefficients were estimated. The applicability of other models of mass transfer has also been verified. It has been shown that the model presented here is the most general and applicable for interpretation of the experimental data obtained when studying the system under consideration 相似文献
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An elastic analog model for controlling the impingement point position in confined impinging jets
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Cláudio P. Fonte M. Ashar Sultan Ricardo J. Santos Madalena M. Dias José Carlos B. Lopes 《American Institute of Chemical Engineers》2016,62(6):2200-2212
Confined impinging jets (CIJs) are highly efficient mixers. The scales of mixing in CIJs are controlled by the opposed jets interaction. A mechanistic model is described here, which accurately predicts the impinging position of the opposed jets for a large range of flow rate ratios. The impinging point position is shown to impact the dynamic properties of the flow and the achieved mixing quality. The opposed jets kinetic energy ratio is shown to have a critical impact on mixing, similar to the Reynolds number. A mixing chamber design relation is proposed and verified for the opposed injectors diameters ratio, , which enables to operate CIJs under optimum mixing conditions for large ranges of flow rate ratios, viscosity and density ratios between the opposed streams. Optimum values have asymptotes for large and small Reynolds number depending on the process stoichiometry, viscosity, and density ratios of the opposed jet streams. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2200–2212, 2016 相似文献
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V.S. Naik-Nimbalkar A.D. Suryawanshi A.W. Patwardhan I. Banerjee G. Padmakumar G. Vaidyanathan 《Chemical engineering science》2011,(12):2616
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. 相似文献
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Jai Prakash Narain 《加拿大化工杂志》1975,53(2):245-251
Jets issuing tangentially to an impermeable flat surface from orifices of finite aspect ratio are termed three-dimensional wall jets. The turbulent flow of viscous incompressible fluid associated with such wall jets has been investigated analytically. Results are presented for the wall jets issuing from orifices of various shapes and several aspect ratios. The maximum velocity shows three regions of decay. The potential core region is followed by a characteristic decay region where maximum velocity decays in a manner dependent on the shape and aspect ratio of the orifice. Following this region, there is a radial wall jet type maximum velocity decay region. All three-dimensional wall jets issuing from any arbitrary cross-sectional orifice decay in a similar manner in this radial decay region. The half-velocity width grows faster in the transverse direction than in a direction normal to the flat surface. The analytical results agree reasonably well with existing experimental results. 相似文献
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Jai Prakash Narain 《加拿大化工杂志》1975,53(3):245-251
Jets issuing tangentially to an impermeable flat surface from orifices of finite aspect ratio are termed three-dimensional wall jets. The turbulent flow of viscous incompressible fluid associated with such wall jets has been investigated analytically. Results are presented for the wall jets issuing from orifices of various shapes and several aspect ratios. The maximum velocity shows three regions of decay. The potential core region is followed by a characteristic decay region where maximum velocity decays in a manner dependent on the shape and aspect ratio of the orifice. Following this region, there is a radial wall jet type maximum velocity decay region. All three-dimensional wall jets issuing from any arbitrary cross-sectional orifice decay in a similar manner in this radial decay region. The half-velocity width grows faster in the transverse direction than in a direction normal to the flat surface. The analytical results agree reasonably well with existing experimental results. 相似文献
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利用电厂循环流化床锅炉现有的结构和设备, 搭建提升管高度60m、内径400mm的超高循环流化床冷态实验台, 重点研究了流化风速和颗粒密度对提升管内轴向和径向空隙率分布的影响。实验结果表明:空隙率分布形式与流化风速和物料密度密切相关, 对于一定的床料高度, 在底部密相区一直有床料堆积的情况下, 随着流化风速的增加, 提升管底部密相区空隙率增大, 上部稀相区的空隙率减小并且其在径向的分布变得更加不均匀;在一定的流化风速下, 密度较小的物料将更多的被带入上部稀相区, 上部稀相区的空隙率减小, 其在径向分布将变得更加不均匀。 相似文献
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Asymptotic methods based on the slenderness ratio are used to obtain the leading-order equations which govern the fluid dynamics of axisymmetric, isothermal, Newtonian, compound liquid jets such as those employed in the manufacture of textile fibres, composite fibres and optical fibres, at low Reynolds numbers. It is shown that the leading-order equations are one-dimensional, and analytical solutions are obtained for steady flows at zero Reynolds numbers, zero gravitational pull, and inertialess jets. A linear stability analysis of the viscous flow regime indicates that the stability of compound jets is governed by the same eigenvalue equation as that for the spinning of round fibres and annular jets. Numerical studies of the time-dependent equations subject to axial velocity perturbations at either the nozzle exit or the take-up point, or both, indicate that the compound jet dynamics evolves from periodic to chaotic motions as the extension or draw ratio is increased. The power spectrum of the inner (round) jet's radius at the take-up point broadens and the phase diagrams exhibit holes at large draw ratios. The number of holes increases as the draw ratio is increased, thus indicating chaotic behaviour. It is also shown that the nonlinear dynamics of bicomponent, compound jets is analogous to that of single-component, annular jets. 相似文献