Entrainment by a concentric jet with particles in the secondary stream

In a two-phase concentric jet the second phase, consisting of solids, influences the development of the jet and the effect of its presence needs to be assessed quantitatively. An experimental study of such a jet with particles in the secondary stream was therefore undertaken. It is seen that particles enhance the mixing.     

Breakup mode of an axisymmetric liquid jet injected into another immiscible liquid

The breakup of an axisymmetric liquid jet, injected vertically upward from a nozzle into another immiscible liquid, into droplets is studied numerically. The unsteady motion of the interface separating two immiscible fluids is followed by solving the Navier-Stokes equations for incompressible and Newtonian fluids in axisymmetric cylindrical coordinates with a Front-Tracking method. The evolution of the interface and the specific surface area of the droplets are in good agreement with experimental results. Three breakup modes, dripping, jetting with uniform droplets, and jetting with non-uniform droplets, are identified. The different modes are shown on a Weber number—the viscosity ratio map.     

Heat transfer between an axisymmetric jet and a plate held normal to the flow

Heat transfer between a submerged jet of water and a flat surface held normal to the flow was studied experimentally over a wide range of plate to nozzle diameter ratios (8 ? D/d < 58). The average heat transfer coefficients were found to be independent of nozzle to plate distance (γ) in the region studied, (γ/d < 7). An equation was developed by separating the target area into the impingement and the wall jet regions. The data were correlated by For nozzle Reynolds numbers 2,000 to 40,000; D/d ? 8 and γ/d < 7.     

Study of mixing in an axisymmetric coflowing liquid jet by coupling L.D.A. to an electrochemical method

Local and simultaneous velocity and concentration fluctuations were analysed in an axisymmetric jet of an aqueous electrolyte solution moving in a codirectional water stream. The determination of the convection velocity of the turbulent eddies as well as correlation between axial velocity and concentration fluctuations was made possible by coupling L.D.A. to an electrochemical technique. The influence of the ratio of the coflowing stream velocity to the jet exit velocity was investigated. The mean velocity and concentration profiles, the turbulence intensity, the integral length scales relative to axial velocity and concentration were also determined.     

稀疏两相射流中颗粒碰撞的数值研究

为了研究稀疏气固两相流动中颗粒间的碰撞行为及其对颗粒扩散的影响,对三维两相湍流射流进行了直接数值模拟。其中对流场控制方程的求解采用有限容积法和分步投影算法,对颗粒的跟踪采用拉格朗日方法,对颗粒间的碰撞采用硬球模型模拟。结果发现,在流场中局部浓度较高的区域颗粒碰撞频繁发生;受局部富集效应和湍流输运作用两方面的影响,颗粒的平均碰撞次数并不是随着Stokes数的增加呈现简单的线性增加,而是在Stokes数为0.1附近存在一个极值;考虑颗粒间的碰撞作用以后,颗粒的分布更加均匀,沿横向和展向的扩散也都有所增加。     

Primary breakup of shear-thickening suspension jet by an annular air jet

An experimental investigation is conducted to study the influence of shear-thickening behavior on the primary breakup process of suspension jets. The primary breakup morphologies of cornstarch–water suspension are observed via a high-speed camera. The unique hardened breakup mode only occurs when the suspension exhibits discontinuous shear thickening (DST). During hardened breakup mode, the oscillating portion of the suspension jet becomes perpendicular to the air direction and keeps cylindrical instead of deforming into a thin sheet or membrane structure. The suspension jets break off into large pieces rather than tiny droplets. The dimensionless number N is established to describe the relative magnitude of the increment of the viscous force and aerodynamic force during the primary breakup process. The primary breakup regime map of Newtonian fluids and shear-thickening suspensions is also promoted based on the dimensionless number N and the Weber number We.     

Measurements of velocity and concentration for a two-phase turbulent jet

The velocity and concentration distributions for an axisymmetric air jet containing sand particles are determined in the fully developed region. Similarity of the profiles is seen beyond 40 nozzle radii downstream from the jet exit and entrainment is gradually suppressed with increase in the initial particle concentration.     

A model for two-phase turbulent mixing in a jet bubble column

Mixing behavior of the two phase air-water turbulent flow in a jet bubble column is examined. The time evolution of the mixing behavior of a liquid tracer in a turbulent air-water flow within a jet bubble column is predicted using a model based on the fundamental governing equations of fluid motion. The predictions of the model are compared with experimental measurements. Measured residence time distributions (RTD) of the liquid tracer within the cone agree well with the predicted values given by the model. For the range of parameters considered in the study, lack of radial mixing and large axial mixing are evident within the cone of the jet bubble column. Use of fundamental mathematical models for the study of hydrodynamics in a two-phase conventional bubble column has been reported earlier (Torvik, 1990; Jakobsen et al., 1993). The present paper extends the use of such models to predict the mixing characteristics in a jet bubble column.     

Quantification of Entrainment Using an Optical Inline Probe

In distillation and absorption processes, entrainment above trays or packings reduces stage and column efficiency. A modified version of the optical multimode online probe enables a seminal insight and, thus, quantification of entrained droplets on various axial and radial positions. A purging mechanism inhibits precipitation of droplets on the front lenses, while telecentric optics and illumination provide distance‐independent and precise imaging of entrained droplets between two valve trays. Experiments were performed in a DN 450 cold flow (air‐water) test rig. The results were compared with noninvasive phase Doppler anemometry data.     

Bubble formation in an annular granular jet dispersed by a central air round jet

An annular granular jet surrounding an air jet at its core is studied experimentally using high‐speed digital photography. The experimental results show that particle bubbles in a periodic manner are formed whether the central air is swirling or not. This flow feature is induced by the intense interaction between the central air jet and the annular granular jet, and it is important for the dispersion of particles by the air jet in the near field. The interaction between the two phases is mainly intensified by higher superficial air jet velocity and the addition of swirl to the central air jet. The bubbling frequency, bubble size, bubble shape, and bubble growth rate are investigated by analyzing a large number of images. In addition, the dispersion angle of granular jet is found to be mainly governed by the radial growth rate of the bubble. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1882–1893, 2013     

循环射流混合槽内液液两相混合特性数值模拟

循环射流混合槽作为一种高效的混合装置在化工过程强化处理技术中具有潜在的工业应用前景。由于缺乏对其内多相体系流动和混合行为的研究,制约了循环射流混合反应器的优化设计与工业化应用。本文选取水和二甲基硅油两相体系,采用计算流体力学软件ANSYS Fluent V16.1中Eulerian-Eulerian多相流模型和SST k-?湍流模型,对两种不同加料方式下循环射流混合槽内液液两相射流中心线速度、离析强度、拉伸率等参数进行研究。研究结果表明：分散相浓度（α_d）增大射流卷吸能耗增大,在l/s<0.4内α_d=1.80%和2.86%量纲为1的射流中心线速度衰减趋势与α_d=6.00%相比减弱51%和21%;在低分散相浓度时,量纲为1的射流中心线速度随Re的增大衰减趋势变化小,在l/s<0.24内Re=6346、9519和12692量纲为1的射流中心线速度衰减趋势与Re=3173相比分别减弱2.60%、2.87%和12.69%。离析强度随混合时间的增大而减小,随周向角度增大呈W形变化趋势。在相含率和雷诺数相同时,对称球状较圆柱状加料达到混合时间减少65.5%;不同喷嘴之间的拉伸率随迹线长度的增大而增大,jet1和jet9位置处的拉伸率与其余喷嘴相比较大;相同喷嘴之间拉伸率随Re的增大而增大,Re=6346、9519和12692的拉伸率与Re=3173相比分别提高289%~320%、418%~454%和607%~667%。     

Throwing of an unsealed heavy body by a two-phase flow

Throwing of a heavy body by unsteady two-phase (powder-gas) flow without using a special seal is considered. Experimental dependences for the body muzzle velocity are presented, which allow one to estimate the feasible kinetic energy of the body at a given gas pressure in the pores and given geometrical parameters of the body.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 3, pp. 119–121, May–June, 1996.     

Model of a two-phase turbulent jet with heterogeneous particle combustion taken into account

Kaliningrad. Translated from Fizika Goreniya i Vzryva, Vol. 24, No. 3, pp. 12–17, May–June, 1988.     

Particle entrainment by axisymmetric jets

The presence of particles can enhance or reduce the entrainment of an axisymmetric air jet. Measurements of particle entrainment in the 2 phase preheated jet were made by the Ricou and Spalding (1961) technique, and the results compared with theoretical estimates. Heating the jet stream improves the entrainment.     

Polygonal deformation of a metallic foil subjected to impact by an axisymmetric indenter

When a stack consisting of layers of soft elastomer and thin metallic film is subjected to low intensity impact by releasing an axisymmetric spherical indenter from a vertical height, the foils buried within the stack undergoes large deformation and fracture. The shape of the deformed area nevertheless remains circular, its radius first increases with the depth from the surface of the stack and then decreases. In contrast, here we show that the symmetry of the deformed area breaks down when instead of a smooth elastomeric layer, one with topographical patterns is used in the stack. The metallic foil deforms through a polygonal area. The size and shape of the polygonal area vary with the flexibility of foil, geometry and dimension of the patterns and the intensity of the impact. For example, for one elastomeric layer decorated with pillars arranged in a square array, the damaged area turns rectangular to hexagonal and then to octagonal with increasing severity of impact, very much similar to polygonal wetting and spreading by a liquid on a patterned substrate.