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.     

分流型芯管开缝结构对导叶式旋风管分离性能的影响

通过改变分流型芯管开缝面积比和开缝位置研究了开缝结构对旋风管压降和不同粒径颗粒分离效率的影响.结果表明,侧壁开缝的分流型芯管能够有效地降低旋风管的压降并且提高不同粒径颗粒的分离效率;随着开缝面积比增大,旋风管压降降低,开缝面积比为3.0使5μm以上颗粒分离效率最高;分流型芯管下部开缝能够提高旋风管的操作弹性.     

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.     

升气管插入深度对旋风分离器流场影响的数值模拟

基于计算流体动力学（Computationalfluiddynamic,CFD）的数值模拟方法,在FLUENT软件平台上,应用大涡（LES）模型模拟了升气管插人深度对旋风分离内部流场的影响。计算结果表明,升气管的插入深度对旋风分离器的流场有很大的影响,随着插入深度的增加,切向速度会减小。本次模拟中还出现了旋涡端部的现象,且随着升气管插入深度的增加,旋涡端部的位置也随着下降,这能够增大分离空间,有利于分离。     

单、双进口对旋风分离器升气管外壁结焦影响的数模分析

利用数值模拟技术,对比考察了旋风分离器采用轴对称双进口和单边切向进口时升气管外壁附近及环形空间的静压和切向速度分布,分析比较这两种进口形式下升气管外切向剪切力和径向压力梯度力对升气管外壁结焦物沉积与积累的影响。结果表明,双入口分离器升气管近壁环向顺、逆压梯度区范围均小于单进口分离器,切向速度沿环向变化不明显,近壁低速易沉积区范围小,且不容易出现油气及催化剂的回流和滞留区,能有效抑制结焦物的沉积;双进口分离器升气管近壁区的平均剪切力比单进口分离器大30%以上,而平均径向压力梯度力比单进口分离器约小17%,能一定程度上削减结焦层厚度,抑制结焦物积累的能力强于单进口。轴对称双进口旋风分离器升气管外壁结焦的倾向将明显小于单切向进口的旋风分离器。     

An Experimental Study of the Performance Factors Affecting Particle Collection Efficiency of the Electrocyclone

An electrocyclone designed with a central discharge wire was built and used to investigate the performance factors affecting its particle collection efficiency by varying the operational conditions and parameters in the particle size range of 0.5 to 10 w m. A voltage of 0 to 9 kV was applied to the discharge wire varying in terms of diameter and length. Two types of vortex finder materials, aluminum and acryl, in three lengths, 2.5, 3.5, and 4.5 cm, were employed to examine the effects of electrostatic force. An increase in applied voltage and a decrease in wire diameter were found to boost collection efficiency, particularly at low flow rates for small particles. Many small particles induced in the cyclone were collected at the bottom of the cyclone cone and in the vortex finder that was situated close to the discharge wire. It was also found that the aluminum vortex finder yields higher collection efficiency than the acryl vortex finder and that the length of vortex finder plays a more important role in particle collection efficiency of the electrocyclone than that of an ordinary cyclone.     

旋风分离器芯管结构改进的试验研究

在PV型旋风分离器的基础上对其芯管结构进行了改进,并通过正交试验得到了一种新的斜切芯管结构。性能对比试验结果表明,当入口气速为20m/s时,相对于基准模型,改进结构的压降平均降低10%,跑损率降低15%。     

旋风分离器入口结构改进及其对“短路流量”的影响

常规切向进口旋风分离器的气流进入旋风分离器后必定要经过排气芯管外壁和筒体内壁之间,因此不可避免会使得相当一部分气流没有经过分离空间而直接从排气芯管底部排出(短路流量),这也是影响旋风分离器分离效率的重要因素之一。在前人工作的基础上,对旋风分离器的进口结构进行了改进:使得旋风分离器的入口具有一定截面角,并借助数值计算技术,分别对传统的和具有一定入口截面角旋风分离器内的三维流场进行了数值模拟,计算了芯管底部的"短路流量",结果表明:进口具有一定截面角可以明显减小芯管底部的"短路流量",这对改善旋风分离器的分离效率具有重要的实际意义。     

气液旋流分离器进口宽高比优化的数值模拟

利用FLUENT提供的RSM和DPM模型对不同入口高度和宽度的气液旋流分离器进行了数值模拟. 结果显示,当增大宽度或高度时切向速度与分离效率减小,但压降降低;当宽度大于环形空间的间隙时,部分进气流量直接作用于排气管上,影响内部流场;减小入口宽度或高度时引起的压降无明显差别,但减小宽度可提高分离效率而高度则相反. 入口高度(a)与分离器筒体直径(D)的比值a/D和宽度(b)与分离器筒体直径(D)的比值b/D约为0.2时,压降基本相同,但分离效率相差约3.6%. a/D约为0.38时,分离效率约为95.6%,压降约为340 Pa;而b/D约为0.25时效率为96.3%,压降约为320 Pa,入口宽度对分离器性能的影响比入口高度更显著.     

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.     

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.     

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。     

差异旋风分离器并联性能测量及流场分析

通过改变旋向和芯管直径,设计了3种差异旋风分离器,并按中心对称方式组成了3种并联方案：相同分离器、旋向差异分离器和芯管差异分离器并联。在冷态实验装置上,测量了单分离器和并联分离器的性能,并利用FLUENT软件分析了并联分离器的流场。结果表明,并联分离器的效率均高于单分离器,且效率-气速曲线未出现“驼峰”;与相同分离器并联相比,旋向交替变化时并联总压降较小,分离效率也更低,但各分离器流量分配均匀,未发现“窜流”现象;当芯管有差异时,并联总压降增大,各分离器进口流量分配不均匀,且进、出口流量平均相差6.0%,公共灰斗中存在“窜流”,旋流稳定性变差,效率降低。为了保证并联分离器的性能,应采用相同分离器对称并联的方式。     

Optimization of the cyclone separator geometry for minimum pressure drop using mathematical models and CFD simulations

The response surface methodology has been performed based on the Muschelknautz method of modeling (MM) to optimize the cyclone geometrical ratios. Four geometrical factors have significant effects on the cyclone performance viz., the vortex finder diameter, the inlet width and inlet height, and the cyclone total height. There are strong interactions between the effect of inlet dimensions and vortex finder diameter on the cyclone performance. CFD simulations based on Reynolds stress model are also used in the investigation. A new set of geometrical ratios (design) has been obtained (optimized) to achieve minimum pressure drop. A comparison of numerical simulation of the new design and the Stairmand design confirms the superior performance of the new design compared to the Stairmand design.     

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.     

并联旋风分离器的旋流稳定性分析

分别选用2台和4台直径300 mm的相同PV型旋风分离器作为分离元件,共用进气管、集气室和排尘室,以中心对称方式组成两种并联分离器,并通过数值模拟比较单分离器与两种并联方案中各分离元件气相流动的特点. 气体介质为常温常压空气,入口气速15~30 m/s. 结果表明,2台或4台并联时各分离元件流量偏差分别不超过0.35%和0.28%,压降最大偏差为0.79%和0.43%,流量分配均匀,灰斗内窜流返混不明显,且4台并联时效果更好. 4台并联时分离元件排尘段的稳定性指数比2台并联或单分离器降低过半,旋流稳定性显著增强. 对称排列的分离元件在公共灰斗中会形成具有自稳定性的对称涡系,对分离元件内旋进涡核的摆动有约束作用,旋流稳定性增强.     

局部磨损对α型旋风分离器内流场及分离性能的影响

以α型旋风分离器为研究对象,基于欧拉-拉格朗日方法,采用雷诺应力模型（RSM）、颗粒离散相模型（DPM）、E/CRC磨损方程对分离器内流场与磨损特性进行数值模拟。通过分析速度矢量、切向速度、颗粒运动轨迹等参数的分布规律,研究了局部磨损对设备内流场及分离性能的影响。结果表明,α型旋风分离器入口正对壁面磨损最为严重,最大磨损率约为1.4×10^-5kg/(m²·s)。磨损引起壁面几何结构的改变,导致气流方向发生偏转,不利于主流的稳定与固体颗粒的分离。随局部磨损的加剧,排气管下口短路流急剧增大,从而导致排气管下口以下区域流体流量减少,外涡切向速度降低;细颗粒的逃逸现象更加明显,粗颗粒运动轨迹趋于重合,更易形成高浓度灰环加剧壁面磨损。与未磨损时相比,局部磨损厚度50mm时,3μm粒径颗粒的分离效率由74.38%降低至54.97%,分割粒径d₅₀由0.73μm增大至2.36μm;设备压降降低了约15.41%。     

Characteristics of the collection efficiency for a double inlet cyclone with clean air

Two single inlet cyclones and a double inlet cyclone were designed and fabricated to evaluate, and compare, their collection efficiencies. Two single inlet cyclones had different inlet sizes and vortex finder diameters. The double inlet cyclone had two inlet parts that divided the cyclone inlet in two. Clean air was introduced to the inlet near the cyclone wall, and particle-laden air was introduced to the inlet away from the cyclone wall. This double inlet made the clean air swirl in the region near the vortex finder, and the particle-laden air swirl in the region close to cyclone wall. The performance of the double inlet cyclone was evaluated at various clean air flow rates, keeping the particle-laden air flow rate constant.The collection efficiency of the double inlet cyclone was found to be 5–15% greater than that of the single inlet cyclone with the same inlet size and vortex finder diameter. As the flow rate of clean air was increased, the collection efficiency increased. This result indicates the possibility of achieving higher collection efficiencies with a double inlet cyclone.     

旋风分离器短路流的估算问题及其数值计算方法的讨论

旋风分离器升气管下口短路流量的大小是评价分离器性能的指标之一,现有的短路流计算方法对升气管下口短路流出现的高度范围的选取并不明确,采用不同的高度范围计算结果可能完全不同,故而分离器设计、开发及应用前后往往需要经历反复的实验验证过程,既费时又费力。通过对双进口及普通单进口分离器径向速度场和轴向速度场的分析,自定义了一种基于数值计算平台的短路流计算方法,要点为根据分离器升气管下口位置横截面上径向流动向心与离心趋势的拐点划分短路流量计算的范围,基本为与升气管同心的环状面,利用CFD软件可以很容易地计算出此环面内下行的流量,即通常意义的短路流量。该计算方法的优势在于能够较准确地定义短路流计算的范围,并且对于新型多进口分离器和普通单进口分离器都适用,计算过程简单、结果可靠。     

熵产方法在旋风分离器内部能耗分析中的应用

应用雷诺应力模型对壁面绝热的旋风分离器的流场进行数值分析,对模拟结果采用熵产分析法和(火用)分析法计算分离器的(火用)损,证实了热力学第二定律研究旋风分离器能量损失的可行性。分别计算了旋风分离器内湍流熵产、黏性熵产、壁面熵产和温差传热熵产。结果表明,壁面熵产和湍流熵产占总熵产的比例分别大于56%和38%,是影响旋风分离器能耗的主要因素。分析了旋风分离器内局部熵产,结果表明,芯管附近体积占旋风分离器体积的10%,其熵产占分离器总熵产的比例高于14%,灰斗入口附近体积仅为旋风分离器体积的5.8%,其熵产占总熵产的比例高于16%,因此芯管附近和排尘口附近是旋风分离器能耗的主要区域。