水力旋流器溢流管结构对微细颗粒分离的影响

针对直径为50 mm的小直径水力旋流器,考察了溢流管插入深度和壁厚以及进口流量对微细物料分离效率的影响,并利用正交分析法得到了溢流管最优的插入深度、壁厚及最适的进口流量。此外,考察了两种套筒式溢流管对水力旋流器分离性能的影响。最后,在最优溢流管结构的基础上,探讨了分流比对分离效率的影响。结果表明：水力旋流器的直筒段具有一定的分离作用;对于微细物料的分离,溢流管采用薄壁且插入深度与水力旋流器直筒段长度相当的设计,有利于提高微细颗粒的分离效率。针对水力旋流器溢流管插入深度与其直径的最佳比例,小直径水力旋流器的比大直径水力旋流器的大,表明它们的分离行为存在着较大的差异。     

Experimental Investigation of a Minihydrocyclone

A phase doppler particle analyzer (PDPA) was used to measure the liquid/solid two‐phase flow pattern in a 25 mm minihydrocyclone. The distributions of velocity, concentration, root mean square (RMS) velocities, and especially the average diameter of the particles were evaluated in this work. The measurements showed that in the upper section of the minihydrocyclone the particles accumulated in the outer helical flow near the line of zero velocity value (LZVV), which probably means that the inner helical flow has a more important influence on the separation. Strong turbulence occurred around the air‐core as well as around the zone near the wall. The RMS value indicated that the transformation of the axial flow direction takes place in the lower section of the conical length.     

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。     

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.     

Studies on the performance of a hydrocyclone and modeling for flow characterization in presence and absence of air core

Hydrocyclones are getting more and more interest from various industries. They are widely used to separate particulates from liquid at high throughput because of their advantages like simple structure, low cost, large capacity and small volume, require little way of maintenance and support structure. Modeling of complex and multiphase flow behavior inside the hydrocyclone is done usually with the help of computational fluid dynamic study. Current study involves experimental investigation of separation performance characteristics of the hydrocyclone using new design parameters. For experimental purpose, a new hydrocyclone was designed with insertion of solid rod, at central portion of conical section of hydrocyclone, inside the hydrocyclone . By which air core could be eliminated effectively and hydrocyclone performance is improved. This effect may be observed due to reduction of radial and axial components of velocity and turbulence in the area near the entrance of the vortex finder. Therefore, the flow field characteristics inside the hydrocyclone with no air core become more suitable for separation. Also the effect of flow rate, vortex finder depths, air core and particle interaction were studied experimentally. A new arrangement was suggested to eliminate the air core formed inside the hydrocyclone. In this case, effect of diameter and height of solid rod inserted inside the hydrocyclone with changing total inlet flow rate was studied experimentally. Three-dimensional geometry and meshing of hydrocyclone is created in Gambit, preprocessor of commercial software—Fluent, for hydrodynamic study.     

Study of Air‐Liquid Flow Patterns in Hydrocyclone Enhanced by Air Bubbles

In order to improve the oil‐water separation efficiency of a hydrocyclone, a new process utilizing air bubbles has been developed to enhance separation performance. Using the two‐component phase Doppler particle analyzer (PDPA) technique, the velocities of two phases, air and liquid, and air bubble diameter were measured in a hydrocyclone. The air‐liquid mixing pump can produce 15 to 60 μm‐diameter air bubbles in water. There is an optimum air‐liquid ratio for oil‐water separation of a hydrocyclone enhanced by air bubbles. An air core occurs in the hydrocyclone when the air‐liquid ratio is more than 1 %. The velocities of air bubbles have a similar flow pattern to the water phase. The axial and tangential velocity differences of the air bubbles at different air‐liquid ratio are greater near the wall and near the core of the hydrocyclone. The measured results show that the size distribution of the air bubbles produced by the air‐liquid mixing pump is beneficial to the process where air bubbles capture oil droplets in the hydrocyclone. These studies are helpful to understand the separation mechanism of a hydrocyclone enhanced by air bubbles.     

LDA measurements of near wall powder velocities in a high shear mixer

In this study, a new method has been developed to measure particle velocity distributions in the near wall region of a high shear mixer by using Laser Doppler Anemometry (LDA). The velocities along the side of the granulator have been measured at different impeller speeds and it has been found that it is possible to obtain tangential and axial velocity data in the dense powder flow up to 4 mm in depth. Moreover, it has been found that the tangential velocity component increases slightly with distance from the wall in the near wall region, indicating a partial slip boundary condition for the solid phase at the vessel wall. It is also shown that the tangential velocity decreases with increased vertical distance to the impeller. The velocity fluctuations, represented by root mean square (rms) velocities, also decrease with increased vertical distance to the impeller and the tangential and axial rms components are found to be of the same order of magnitude.     

溢流管结构对天然气水合物用旋流器分离性能的影响

建立了主直径100 mm的旋流器模型,采用计算流体力学(CFD)方法研究了溢流管内径、插入深度及壁厚对旋流器分离天然气水合物性能的影响规律。结果表明,入口流速为9 m/s时,随溢流管内径增大,水合物分离效率增大,砂的分离效率降低,旋流器的压力降逐渐减小;随溢流管壁厚增大,水合物和砂的分离效率稍有增大,旋流器的压力降先增大后减小;随溢流管插入深度增大,水合物分离效率先减小后增大,砂的分离效率先增大后减小,旋流器的压力降波动较小。溢流管内径对旋流器分离天然气水合物性能的影响最大,插入深度次之,壁厚的影响最小。     

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。     

MEASUREMENTS OF MEAN VELOCITY PROFILES IN A HYDROCYCLONE USING LASER DOPPLER ANEMOMETRY

A quantitative study of the axial and tangential components of the mean velocity in a 3'-hydrocyclone using laser doppler anemometry has revealed multiple reverse flows in the vortex core. Flow visualization by dye injection shows that these flows are coherent over a significant portion of the hydrocyclone and that little radial mixing occurs between these secondary flows and the outer helical flow. A 2:1 contraction in the vortex finder plays an important role in causing four distinct simultaneous countercurrent flows in the conical section of the hydrocyclone.     

Short‐Circuit Flow in Hydrocyclones with Arc‐Shaped Vortex Finders

Several new arc‐shaped vortex finder structures were developed to restrain the circulation flow and reduce short‐circuit flow. These problems were investigated by conducting laboratory experiments and using a computational fluid dynamics numerical simulation method. To verify the accuracy of the numerical simulation, a type A vortex finder was employed to perform a particle image velocimetry test under identical working conditions. Then, these new structures were compared with a type O vortex finder to reveal the differences in pressure field, velocity field, and separation performance. The arc‐shaped vortex finder was able to restrain the circulation flow and reduce the maximum pressure drop at the outer wall of the vortex finder.     

分流型芯管对导叶式旋风管内颗粒逃逸的控制

Experimental and computational fluid dynamics was used in this study to predict the escape particles and evaluate the performance of PSC type cyclone tube with slotted vortex finder.The simulation results showed that the PSC type cyclone tube could remove the particles with a diameter greater than 5 μm.The PSC type cyclone tube increased the grade efficiency of particles with a diameter greater than 2 μm as compared with the Shell type cyclone tube.Short circuit flow occurred around the vortex finder slots and there was almost no short circuit flow under the vortex finder inlet.Most small particles escaped from vortex finder slots of the PSC type cyclone tube.The slotted vortex finder could develop “upwards flow” near the vortex finder inlet outside wall and control the escape particles under the vortex finder inlet.The force analysis of particles near the slotted vortex finder slots showed that gas flow carried the particles with a diameter smaller than 3 μm out the separator.     

Performance of a New Geometry of Deoiling Hydrocyclones: Experiments and Numerical Simulations

A new geometry of liquid‐liquid hydrocyclones is proposed seeking to perform the separation of oil emulsified in water. The hydrocyclone performance was investigated by means of a factorial experimental design (2³) leading to a total of ten experiments. The results enabled the determination of empirical mathematical models that describe capacity, total separation efficiency, and flow ratio as a function of oil concentration in the feed inlet, operating pressure drop, and presence or absence of a vortex finder in the geometry. Numerical simulations were also carried out to further understand the flow field characteristics in the studied hydrocyclone.     

压载水旋流器结构因素对分离性能影响分析

随着全球贸易和船舶运输的发展,压载水对环境的影响越来越大。水力旋流分离设备是压载水净化的重要固液分离设备。本文使用计算流体力学,建立数学模型模拟压载水旋流分离过程,模型包括多相湍流雷诺应力模型RSM、处理气液界面的自由表面多相流动模型VOF、处理固体颗粒运动规律的离散相模型DPM。通过数值模拟计算柱段长度、底流口直径和溢流口直径这几个关键因素对旋流器内部流场和分离效率的影响,获得了各个因素对分离效率的影响规律：柱段长度变化对旋流器分离效率的影响不大;底流口直径对旋流器压力降的影响不明显,但对分流比的作用比较大;溢流管直径的增大有助于降低能耗和增大溢流口流量,但随着溢流管直径的增大,分级粒度变大。这些规律为高效旋流分离净化压载水奠定了基础。     

Collection efficiencies of various designs of post‐cyclone

Post‐cyclone (PoC) is a novel secondary dust separator, which collects a certain fraction of the particles escaping through the vortex finder of a reverse flow cyclone. Due to the residual swirl in the vortex finder, the particles in the effluent air are concentrated at the wall of the vortex finder in an outer annulus. The particles in the outer annulus are split from the main stream and collected in a bleed flow. This paper presents the experimentally determined collection efficiencies of various designs of PoC. Depending on the design, operating conditions and the size and density of the particles, PoC can reduce the emission of the parent cyclones by 5% to 50%. In some experiments, the bleed flow from PoC is recycled back to the inlet of the cyclone. Significant improvement in the removal of fines occurs when the bleed flow is recycled to the inlet.     

水力旋流器新型出口挡板结构对分离性能的影响

针对小直径水力旋流器,设计了不同内置挡板式的溢流管和底流管,实验研究了新型出口挡板结构对水力旋流器分离性能的影响。研究结果表明：内置挡板溢流管适用于处理量较大的工况,与传统溢流管相比,分离效率略有降低,但在高流量下其压降的降低幅度可达11.11%,挡板宜采用相对较窄、较短、三块120°间隔设计方式;底流管内置挡板采用十字交叉结构可稳定内旋流,使分离效率最大可提高5.96%;新型内置挡板的溢流口与底流口相耦合,可同时实现提高分离效率和降低压降的目标。此外,在相同情况下,发现溢流管内置挡板可消除水力旋流器内部的“空气柱”,据此推断“空气柱”并非由内部空气形成,而是其内部负压中心形成的某种湍流程度较高的强制旋流涡。     

Experimental Investigation of the Natural Vortex Length in Tangential Inlet Cyclones

In this study, the natural vortex length has been investigated experimentally under the effects of inlet gas velocity, diameter, and insertion length of the vortex finder and surface friction in a special designed cyclone which has a double cylindrical body without cone. Experimental results show that, comparing to the other parameters, the height of the frictional surface and inlet gas velocity affect the natural vortex length considerably. The natural vortex length increases with the increase of inlet velocity and with the decrease of the height of the frictional surface. It was also observed that when the diameter of the vortex finder increases, the natural vortex length increases up to certain point and starts to decrease after that.     

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。     

多进口旋流器流场特征及分离性能

为了改善单进口旋流器稳定性差、分级效率低等问题,本文提出了多进口旋流器结构。通过数值模拟方法,在恒定入料工况下,对比分析了单、二、三、四进口旋流器的流场特征和分离性能。研究结果表明：增加旋流器进口数量,会对旋流器流场和分离性能产生积极影响,有利于旋流流场径向压力的增大,且进口数量为偶数时,流场径向静压力增强效果更好;旋流器柱段区域流场切向速度增大,有利于强化旋流器分离能力。同时使用Mixture耦合RSM模型预测了离散相CaCO₃颗粒的分离效率,结果表明多进口旋流器可以在低速度入口条件下完成离散相的高精度分离。入料速度为3m/s的工况条件下,多进口旋流器分离50μm、57.5μm颗粒的底流分配率较单进口旋流器分别提升了10.60%、5.59%,对抑制旋流器溢流产品错配率和提高分级精度有积极的影响。因此,增加旋流器进口数量,可以有效提升旋流分级效率和分离精度。     

Pressure gradients,voidage and gas flow in the annulus of spouted beds

Parallel measurements of pressure gradients with a differential pressure probe and voidage profiles with a fibre optic system have been carried out to study gas flow distributions in the annulus of spouted beds. The observation of Grbavcic et al. (1976) that for a given fluid‐solid combination and column geometry the annulus pressure gradient at any bed level is independent of bed depth was corroborated again. Calibration curves of pressure drops versus superficial gas velocities for beds of voidage higher than the loose‐packed voidage were obtained by applying the Ergun (1952) equation, making it possible to estimate superficial gas velocities in the annulus using the static pressure gradient method. The local superficial gas velocity in the annulus was found to be higher in a deep bed than in a shallow bed of the same material, contrary to the conclusion (Grbavcic et al., 1976) that, for a given fluid‐solid combination and column geometry, the annulus fluid velocity at any level is independent of bed depth. Theoretical models and equations which do not account for the conical geometry near the bottom were found to underpredict superficial gas velocities in the annulus. Increasing the spouting gas flow was found to increase the net gas flow through the annulus.