Theoretical and experimental studies of confined vortex flow

A study of the air flow characteristics is reported for a vortex chamber 122 cm in diameter consisting of an upper cylindrical section 61 cm high and of a lower conical section 108 cm high. Measurements were made with a five-channel pressure probe of the radial profiles of tangential and axial velocities, with varying inlet air velocity and axial distance from the top of the chamber. Measurements of the static pressure profiles were made simultaneously. Finally, the angle of flow of the air entering through the single tangential inlet could be adjusted, and its effects on the flow recorded. From these results and from a theoretical analysis, generalized expressions for the tangential velocity profiles were obtained for the two regions of flow, forced-vortex and quasi-free vortex, which prevail in a confined vortex chamber, as a function of the entrance air velocity and of the radius at the point considered only. The angle of entering air was found to have no effect on the tangential velocity and only a minor effect on the static pressure distribution. The outlet diameter of the chamber was found to have a large effect on the profile of the axial velocities, reflecting the influence of the chamber static pressure on the latter.     

Measurements of flow characteristics in a confined vortex flow

A study of air flow patterns by hot-wire anemometry is reported for a vortex chamber consisting of an upper cylindrical section 122 cm in diameter and 61 cm high and a conical bottom section 122 cm high. Quantitative data are presented for flow angles, profiles of mean tangential and axial velocities, and radial distributions of tangential and axial intensities of turbulence as a function of air entrance velocities of 1.6, 2.4 and 3.2 m/s, and axial distance from the top of the chamber. In general, the quantitative results confirm the theoretical predictions and the experimental trends reported in the literature. In particular, they fully support the conclusion that the flow pattern is relatively insensitive to the entrance volumetric flow rate. A generalized correlation is presented for the axial velocity distribution. Preliminary correlations are also presented for the tangential velocity distributions in the core and in the annular region of the vortex near the wall. These were found to be functions of the axial location and of the air entrance velocity.     

不同流量条件下导叶式旋流器内部流动的数值模拟

应用Fluent软件和雷诺应力模型(RSM)对导叶式旋流器内部三维强旋湍流流动进行了数值模拟,考察了不同入口流量对旋流器内速度场的影响。研究结果表明,旋流器内径向速度远小于切向速度和轴向速度,锥段的切向速度明显小于柱段的切向速度;随着流量的增加,各向速度均增加,最大切向速度的分布直径并不随流量的变化而改变,且最大切向速度位于准自由涡与准强制涡的分界处。通过计算还发现,在旋流器圆柱段存在循环流和短路流,锥段的上行区域均小于柱段,而且截面越靠底流口,上行区域越小。     

Flow patterns in conical and cylindrical hydrocyclones

Using a two beam, 300 mW laser Doppler velocimeter, the tangential and axial velocity fields were determined for the water flow in a 102-mm modular hydrocyclone. The body of the equipment could be changed to transform it into a conical or a flat bottom hydrocyclone. During the tests the pressure drop and the diameter of apex and vortex were varied and the axial and the tangential velocities and their turbulence intensity were measured. The results shows that the inlet pressure affects only the magnitude of the velocities, but does not change the flow pattern. The tangential velocity is similar in both types of hydrocylones while the axial velocity is different. In both hydrocyclones the axial velocity is a function of the radial position but, while it is a linear function of the vertical coordinate in the cylindrical hydrocyclone, this is not the case for the conical vessel.     

Flow Characteristics in a Vortex Chamber

In this article we examine confined swirling flows using the integral equations of continuity and energy, along with the minimum pressure criterion. The pressure drop and the core size have been studied in the swirling confined vortex chamber. Both the n = 2 vortex model, with reverse and non‐reverse flow, and the free vortex model have been used at the vortex chamber exit plane. The influence of vortex chamber geometry, such as contraction ratio, inlet angle, area ratio, aspect ratio, and Reynolds number, on the flow field has been analyzed and compared with the present experimental data. The pressure drop across the vortex chamber differs from that in pipe flow, due to the mechanism of swirl flow that depends mainly on the intensity of tangential velocity. If the chamber length is increased, the vortex decays producing a weaker tangential velocity (less centrifugal force) that leads to less pressure drop. Based on the present theory, a new approach to determine the tangential velocity and radial pressure profiles inside the vortex chamber is developed and compared with the available experimental data. It shown that the n = 2 vortex model with reverse flow gives better results for strongly swirling flow.     

Effects of the Inlet Section Angle on the Flow Field of a Cyclone

The gas flow fields of a cyclone with different inlet section angles have been studied numerically. The gas flow fields were simulated by means of the Reynolds Stress Transport Model (RSTM). The velocities and pressure drop profiles of these cyclones were investigated. The shortcut flow rates at the bottom of the vortex finder were calculated with different inlet section angles. To analyze the relationship between the inlet section angle and the vortex finder insertion deepness, this paper details the shortcut flow rates at the bottom of the vortex finder for three vortex finder insertion depths. The results indicate that the inlet section angle can decrease the shortcut flow from the bottom of the vortex finder, which has practical importance for the improvement of the separation efficiency. The inlet section angle can also decrease the pressure coefficient of a cyclone. When the inlet section angle is 45 °, the level of decrease is up to 30 %. However, the effect of the inlet section angle on the separation performance is related to the dimension of the vortex finder, i.e., the insertion depth and diameter of the vortex finder, and the effect is different when the cyclone has different vortex finder insertion depths.     

旋流数为1.0的强旋湍流两相流动的PDPA实验

采用相位多普勒颗粒测速仪 (PDPA)对旋流数为 1 0的轴向和切向进风的圆柱形旋风筒内强旋湍流气粒两相流动进行了测量研究 ,并与旋流数为 0 47、 1 5和 2 0 8的实验结果进行了对比分析 ,指出了旋流数变化对两相流场及两相湍流特性的影响 .     

新型气液逆流撞击洗涤喷嘴的优化

针对一种新型气液逆流撞击式洗涤喷嘴,通过冷模实验,采用溶氧法考察了不同结构喷嘴的气液两相传质性能。结合解析率及流型变化,考察了喷嘴出口直径、切向进液口倾角、旋流室收敛段锥角、切向进液口直径、喷口长度5个参数对传质的影响,确定了优选喷嘴的结构尺寸,分析了该优选喷嘴在不同操作条件下(气速、表观液气比和轴切比)的传质效果。结果表明,优选喷嘴在轴切比为0.4~0.6且气速较高时传质效果较好。     

LASER-BASED FLOW MEASUREMENTS OF DILUTE VERTICAL PNEUMATIC TRANSPORT

Dilute vertical pneumatic transport in a vertical lifter was studied using the sophisticated measurement techniques of laser Doppler anemometry (LDA) and phase Doppler anemometry (PDA). The vertical lifter consisted of a lower fluidized silo, an upper receiving tank, and a connecting vertical transport pipe made of clear glass. The experimental study was performed in order to get detailed information of the complex gas-particle flow behavior in a dilute vertical conveying system. Particle diameter, axial particle, and tangential particle velocities, as well as root mean square velocities, were measured simultaneously for different flow conditions. In addition, overall solid mass fluxes were obtained using weighing cells. Smooth and spherical zirconium oxide (ZrO₂) solids were applied with two different particle size distributions. Measurements were performed using different flow rates of air. The air inlet condition was varied in order to study its effect on the flow behavior. The particle diameter measurements show that no axial or radial segregation by size occurs for this transport condition. The results show that the particle velocity is independent of the particle size as well. The axial velocity profiles at different heights are almost identical and flat, which indicates fully developed turbulent pipe flow. The turbulent velocity measurements show that turbulence is mainly caused by the velocity gradients, and not by particle-particle collisions in dilute flow. The solid mass flux measurements show the importance of optimum inlet condition and how this influences the mass flux.     

LASER-BASED FLOW MEASUREMENTS OF DILUTE VERTICAL PNEUMATIC TRANSPORT

Dilute vertical pneumatic transport in a vertical lifter was studied using the sophisticated measurement techniques of laser Doppler anemometry (LDA) and phase Doppler anemometry (PDA). The vertical lifter consisted of a lower fluidized silo, an upper receiving tank, and a connecting vertical transport pipe made of clear glass. The experimental study was performed in order to get detailed information of the complex gas-particle flow behavior in a dilute vertical conveying system. Particle diameter, axial particle, and tangential particle velocities, as well as root mean square velocities, were measured simultaneously for different flow conditions. In addition, overall solid mass fluxes were obtained using weighing cells. Smooth and spherical zirconium oxide (ZrO₂) solids were applied with two different particle size distributions. Measurements were performed using different flow rates of air. The air inlet condition was varied in order to study its effect on the flow behavior. The particle diameter measurements show that no axial or radial segregation by size occurs for this transport condition. The results show that the particle velocity is independent of the particle size as well. The axial velocity profiles at different heights are almost identical and flat, which indicates fully developed turbulent pipe flow. The turbulent velocity measurements show that turbulence is mainly caused by the velocity gradients, and not by particle-particle collisions in dilute flow. The solid mass flux measurements show the importance of optimum inlet condition and how this influences the mass flux.     

不同旋流数下湍流气粒两相流动特性的PDPA实验研究

利用相位多普勒仪 (PDPA)系统研究了不同旋流数下突扩旋风筒内气粒两相湍流特性的变化规律 .在相同的进口形状和总风量的条件下 ,分别测量了旋流数为 0、 0 .5和 1.0时气相和颗粒相的轴向、切向的平均速度和脉动速度 .结果表明 :旋流数的变化对轴向速度的分布和切向速度的似固核 -位涡结构 ,以及两相脉动速度和两相湍流各向异性都有比较明显的规律性影响 ;总体上 ,旋流对两相湍流起抑制作用 ,但随旋流数的增大 ,两相湍流脉动及其各向异性都有先减弱 ,后来又有所增大的趋势     

新型旋风分级器流场特性及颗粒分级性能

针对传统旋风分级器分级效率较低的难题,本文设计了一种中部进风、顶部重力进料式新型旋风分级器,利用数值模拟和试验手段对其流场特征及分级性能进行了研究。模拟结果表明,新型旋风分级器内存在若干旋涡,主气流进入分级器后形成由上、下两个旋涡构成的主分级流场,上部旋涡均为上行气流,下部旋涡为切流返转形式;二次气流形成的细颗粒淘洗旋涡具有近壁面处高转速、中心区快速上升的特点,最大轴向速度达16.5m/s,可强化对边壁处浓集颗粒的剪切分散和淘洗作用,对主分级流场切向速度影响较小,但可使其轴向速度值最大增加100%,这将缩短细颗粒的停留时间;主分级流场与淘洗流场相互作用形成分区流动,具有较明显的动态边界,为粗、细颗粒的定向分离提供了力场基础。试验表明,二次气量占比约20%,主、二次气流气速分别为14m/s和20m/s时,牛顿分级效率可达88%,分级精度指数K值最小为1.84,此时新型旋风分级器具有较高的分级精度。     

Flow field in the freeboard of vortexing fluidized bed

A systematic investigation on the flow field in a vortexing fluidized bed cold model was reported. The gas velocity profiles within the freeboard with diameters of 0.19 m and 0.29 m were measured by using a five-hole pitot tube. A new parameter, called vortex number, V_or defined as the ratio of tangential velocity to axial velocity of the swirling gas stream, was proposed for representing the swirl intensity. V_or is found to be increased with secondary air velocity, and decreased with primary air velocity and diameter of secondary air nozzles. It is also found that the profile of swirl flow is significantly affected by the arrangement of the secondary air nozzles. The effects of inserted length of secondary air nozzles and geometric structure of expansion section on the swirl flow are also studied. Based on the experimental data, a correlation is presented to estimate the vortex number. Vortex number is found to be a function of the geometric structure of exhaust tube, diameter of secondary air nozzle and tangential air flow rate.     

旋流板分离器的结构对三维流场的影响

引言 旋流式分离器种类很多[1-4],其中浙江大学发明的旋流板在传质和双相分离过程中均得到广泛应用[5-9].旋流板分离器是利用导向叶片使气体做旋转运动,从而产生离心力,达到气液或气固分离的目的.     

柱状旋流分离器零轴速面分布特性模拟分析

采用雷诺应力模型对柱状旋流分离器气相流场中的零轴速包络面分布进行了数值模拟分析,考察了旋流不稳定性、流速以及结构参数变化对其分布的影响。指出由于分离器旋转流动不稳定性的固有存在,零轴速边界在整个分离空间会呈非轴对称的扭曲状态;在研究速度范围内,流场处于自模化区,分离器运动相似,入口速度变化对零轴速边界的分布影响不大;升气管直径与入口面积对升气管入口区域的零轴速边界分布影响较大,随升气管直径的减小和入口面积的增大,零轴速边界逐渐收缩。远离升气管入口区域,升气管直径与入口面积的影响减弱,零轴速边界宽度逐渐增大,并趋于一致;使流场趋于稳定的升气管直径与入口面积,截面零轴速边界会保持较好的圆度。     

不同操作参数下动态水力旋流器内部油水两相流动的数值模拟

根据计算流体动力学(CFD)的方法,应用Fluent软件对动态水力旋流器内部油水两相流场进行数值模拟,考察了不同入口流量及转筒转速下旋流器内速度场与油水两相的分布情况。结果表明:动态水力旋流器内切向速度呈双涡结构(准自由涡与准强制涡);轴向速度明显小于切向速度且不存在零速度包络面,油相集中于旋流器轴心形成油核,随着流量及转速的增加,各相速度及中心油核浓度均增加。     

多旋臂气液旋流分离器内气相流动特性分析

为考察费托合成过程中用于油气分离的新型多旋臂气液旋流分离器内气相流场分布特性,明晰离心分离效果,采用RSM湍流模型对分离器气相流场进行模拟研究,所得压降与实验数据吻合较好,表明该模型适用于模拟该分离器。根据结构特点和压力分布特性,将分离器划分为四个区：进料管区、旋臂区、环隙区和分离区。结果表明,气体流经旋臂时运动方向改变产生的阻力损失占总阻力损失的60%以上;经旋臂排出后气体分为三股,即沿封闭罩逆时针上行流和下行流,以及沿旋臂与进料管之间区域顺时针上行流;环隙区轴向高度1.472 m,周向位置45°, 135°, 225°, 315°附近形成轴向速度为零的横向旋涡,同时气体在环隙区内径向位置|r/R|=0.972处出现切、轴向速度的最大值,且运动角度均稳定维持在37.43°附近;分离区内上下行流界限清晰(位于|r/R|=0.854)且切向速度符合Rankine涡结构,拟合得到平均准自由涡旋涡指数n=0.697;旋臂附近区靠近外侧壁面处(|r/R|=0.893)和环隙区内|r/R|=0.972处的切向速度均对入口气速的变化较敏感。     

Flow Patterns in Mini‐Hydrocyclones with Different Vortex Finder Depths

Two‐phase flow patterns in a mini‐hydrocyclone with different insertion depths of the vortex finder were measured by a phase Doppler particle analyzer. The distributions of velocity, concentration, root‐mean‐square velocity, and average diameter of particles were evaluated. A deeper insertion of the vortex finder led to smaller tangential velocity at the cross section near the column cone interface. When the vortex finder insertion depth did not reach the column cone interface, the vortex finder was inserted deeper and the line of zero velocity value migrated more distinctly inward. When the vortex finder insertion depth reached or exceeded the column cone interface, strong turbulence occurred near the vortex finder. The distributions of the axial velocities of particles and root‐mean‐square velocities indicated that circulation flow existed at the bottom part of the mini‐hydrocyclone.     

Effect of a Stick on the Flow Field in a Cyclone and the Pressure Drop Reduction Mechanism

Measurements of the flow field in a cyclone separator with and without a reducing pressure drop stick (Repds) showed that the Repds reduces the peak tangential velocity, the axial velocity gradient, and the radial gradients of static and total pressure and reverses the axial static pressure gradient. These changes reduce the energy consumed by the rotating kinetic energy, the internal friction, the turbulent kinetic energy, and the drag of the negative pressure difference. The results are used to discuss why the separation efficiency remains high while the pressure drop is reduced. The results also show that a 24% "short flow" occurs near the cyclone entrance. Analysis of the changes in the flow field and the pressure drop due to the thin stick shows that the Repds increases the pressure drop in the outer vortex zone and reduces the pressure drop in the inner vortex zone. Therefore the pressure drop reduction with the Repds is due to its wake vortex, which leads to the hypothesis that the pressure drop in turbulent flow can be reduced by adding vortexes.     

旋风分离器高温流场的实验测量

引言 对旋风分离器内流场的认识是研究其分离过程的基础.长期以来,人们对旋风分离器内流场的结构、速度分布等进行了大量的测量和分析,认识到旋风分离器内是一个三维强旋旋湍流场.