Numerical study on the performance of swirl tube based on orthogonal design

Here, an axial flow cyclone separator is design is proposed. The effects of varying the structural parameters and operating conditions on pressure drops and separation efficiency were investigated via a numerical simulation approach. The results show that of the three structural parameters considered, the distance between the diffuser and blade is the most significant factor impacting separation performance compared to the blade pitch and blade shaft diameter. Increasing the distance between conical outlet and blade can decrease its pressure drops and increase separation efficiency; while increasing the shaft diameter can increase pressure drops, and the increasing blade pitch can decrease both the pressure drop and the separation efficiency. The pressure drop of the optimized swirl tube was 102.1 Pa, with a corresponding separation efficiency of 95.04% for 100 μm particles at an extraction ratio of 10%. Further, the cut-off particle size can reach 3 μm, demonstrating that the swirl tube offers good separation performance and has the potential to be widely applied in industrial gas–solid separation applications.     

Effects of helical fins on the performance of a cyclone separator: A numerical study

This study aimed to investigate the separation performance of a cyclone separator after reshaping its cylindrical body by installing the helical triangular fins. A numerical simulation based on Fluent was adopted to perform an orthogonal test to optimise the structure of the cyclone separator with helical triangular fins. Three structural parameters of the helical triangular fins were selected as optimisation variables: base width, fin size, and fin pitch, and their influences on the evaluation indices of the cut-off diameter were investigated. The optimal combination scheme was determined by range analysis, and the cyclone separator performances before and after optimisation were compared and analysed. The significant influence of the structural parameters on the cut-off diameter was in descending order as the fin pitch, fin size, and base width. For particles with diameter of 0.1, 0.5, 1, 2, and 3 μm, the separation efficiency of the cyclone separator with optimized helical triangular fins increased by 7.4 %, 15.9 %, 20.1 %, 10.9 % and 14.8 % respectively. Moreover, the cut-off diameter of the finned cyclone separator is reduced by 30.7 %, while the pressure drop is only increased by 6.6 %. The short circuit flow and back-mixing were alleviated, thereby considerably enhancing the stability of the flow field. Therefore, the finned cyclone separator was found to play a critical role in increasing the separation of fine particulate matter.     

CFD-DEM simulation and optimization of gas-cyclone performance with realistic macroscopic particulate matter

Most of research concerns have been focused on developing new methods and parameters to make the cyclone separator performance better. In this work, the inverse-flow cyclone type geometry was performed and optimized through the modulation of changing the position and dimensions of the involute inlet portion and cyclone barrel section length at a fixed inlet air velocity of 30 ms^?1. Cyclones of different inlet sizes and portions were computationally modeled which named as cyclones I, II, III, IV, and V. The study was successfully accomplished for two heterogeneous groups of particulate matter mixed with air flow for applications pertinent to agricultural engineering. To capture the phenomena of constitutive air-granular materials behavior in the optimized separator, numerical simulations were generated using one-way coupling of commercial ANSYS-Fluent® 18.0 (CFD) and Rocky® 4.13 (DEM) software, which is considered as the first head start research approach in the cyclonic separation and purification field. Discrete Element Method (DEM) which was represented by Rocky® package simulates the movement of each particle individually, taking into consideration the interaction and collision of the particles. Whereas, the highly curved streamlines and the chaotic turbulence of the continuum air flow in the cyclone separator were modeled through the Computational Fluid Dynamics (CFD-Fluent®) technique using advanced turbulence model RNG $k-\epsilon$. The numerical results successfully captured the effects of new geometrical modifications done on the original cyclone separator. Numerically, the cyclone inlet height significantly improved the cyclone performance by increasing the separation efficiency, cleaning efficiency, and cyclone effectiveness, while other parameters had a negative effect. These data were useful for considering cyclone (III) as the most suitable modification and optimization design geometry for harvesting jojoba seeds with the lowest operation cost and highest performance.     

DUST STRANDS IN CYCLONE SEPARATORS AT LOW DUST CONCENTRATION

State of the art in calculating a cyclone separator is the application of the equilibrium theory and taking the formation of dust strands into account as well. The latter process does not depend on particle size mainly. An ideal flow pattern for the formation of dust strands is the so called Dean-vortex: it is being realized favorably in the axial flow cyclone. A dust strand can be produced down to a raw gas concentration C₀ ≈ 10^-5. Then, it is being exhausted through one or few holes in the mantle of the axial cyclone applying bleeding of about 10 % of the volume flow Separating its dust in a bin cyclone and recirculating the binflow gas to the main, axial cyclone completes this high performance cyclone separator. Dimensional analysis shows that the clean gas concentration c₁ mainly depends on the swirl W_tan/w_ax, the raw gas concentration c₀and on Reynolds number. For usual dust conditions a clean gas concentration c₁ ≤ 50 mg/m³ is feasible.     

Modification of the cyclone separator geometry for improving the performance using Taguchi and CFD approach

ABSTRACT

The cyclone separator performance has been affected by its high-pressure drop. The main geometric ratios such as outlet diameter, inlet width and inlet height and total height have been preferred to reduce the pressure drop and improve the performance of cyclone separator. These standard geometric values have been altered with the aid of design of experiment technique by Taguchi method for reducing the pressure drop. This changed new design produce low-pressure drop compared with the standard cyclone separator. Moreover, the collection efficiency of the new design is high when compared with standard cyclone separator. The pressure drop, Euler number, cut-off diameter and efficiency of the standard and new cyclone separator have been compared with the results of mathematical and computational fluid dynamics technique (CFD). The Reynolds stress turbulence model and discrete phase model have been used for simulating the cyclone separator in CFD. An acceptable agreement has been obtained between these results.     

DUST STRANDS IN CYCLONE SEPARATORS AT LOW DUST CONCENTRATION

Abstract

State of the art in calculating a cyclone separator is the application of the equilibrium theory and taking the formation of dust strands into account as well. The latter process does not depend on particle size mainly. An ideal flow pattern for the formation of dust strands is the so called Dean-vortex: it is being realized favorably in the axial flow cyclone. A dust strand can be produced down to a raw gas concentration C₀ ≈ 10^?5. Then, it is being exhausted through one or few holes in the mantle of the axial cyclone applying bleeding of about 10 % of the volume flow Separating its dust in a bin cyclone and recirculating the binflow gas to the main, axial cyclone completes this high performance cyclone separator. Dimensional analysis shows that the clean gas concentration c₁ mainly depends on the swirl W_tan/w_ax, the raw gas concentration c₀and on Reynolds number. For usual dust conditions a clean gas concentration c₁ ≤ 50 mg/m³ is feasible.     

导叶式旋风管内短路流颗粒夹带的研究

采用数值模拟方法,结合试验与理论分析,研究Shell型导叶式旋风管内短路流颗粒夹带问题。结果表明:Shell型旋风管直筒芯管下口存在短路流现象,计算得知短路流量占进口总流量的39.3%。理论分析发现,短路流主要夹带粒径小于9μm的颗粒,短路流夹带颗粒临界粒径为9μm。另外,数值模拟跟踪颗粒逃逸的轨迹证明,Shell型旋风管能将粒径大于9μm的颗粒全部除尽;粒径小于9μm的颗粒既有经排尘口返混逃逸,又有短路流夹带逃逸,其中短路流夹带逃逸占主要部分,且随着粒径的增加,经芯管下口短路夹带逃逸的数目减小。     

多联机旋风式油气分离器内管与进气碰撞的数值模拟

以小型多联机用旋风式油气分离器为研究对象,建立三维稳态数值模型。气流场选用重整化群湍流模型(RNGk-ε),油滴轨迹采用随机轨道(DRW)模型,研究内管长度、筒体高度和进气碰撞程度对油气分离器内部流场分布、分离效率和压降的影响。发现大部分油滴在内管截面以上的筒体空间内完成分离;油气分离器所需内管长度与筒体高度比值随进气速度的增加而减小;进气碰撞程度(油气分离器横截面上内管下边缘与进气管上边壁的垂直距离与进气管径的比值,即h1/di)小于26.57%,进气速度大于23.09 m/s时,更容易获得稳定的旋流流场。     

出口结构对双蜗壳式旋风分离器内流场的影响

用智能七孔球探针测试仪对不同出口结构的双蜗壳式旋风分离器内不同位置的三维速度及压力进行测量,从而获得不同结构参数对流场的影响。实验结果表明,排尘锥结构具有一定的稳流作用,有利于分离器的分离;分流型芯管的开缝有分流的作用,降低了芯管内的气流旋转强度,使上下行流都有所减少,旋风管中心附近以及边壁附近的切向速度都有所减小;分流型芯管的特有的缩口结构使不同截面上的切向速度的最大值都有所增加,距离缩口越近增加越强烈。     

Effects of Exit Tube Diameter on the Flow Field in Cyclones

A number of cyclones with different exit tube diameters have been simulated with CFD in this study. Results show that the exit tube diameter influences not only the velocity magnitude, but also the shape of the velocity profiles within cyclones. Depending on the diameter of the exit tube, the axial velocity profiles can exhibit a either maximum or a minimum on the axis. If the exit tube diameter is small, the central flow has a jet-like appearance. On the other hand, axial velocity dip in the profile can be observed near the center in a cyclone with a large gas exit tube. In addition, the well-known double vortexes, which commonly are present in a cyclone of practical design, do not exist in a cyclone with an excessively large exit tube. Quantitative comparison of velocity distribution shows that the tangential velocity increases as the exit tube diameter is reduced, giving rise to higher particle collection efficiency. Usually, the pressure drop decreases with increasing exit tube diameter. However, if the exit tube size is excessively large, the pressure drop may start to increase. Practically, cyclone with an excessively large exit tube should be avoided.     

旋风分离器减阻杆减阻的PIV实验研究

采用先进的PIV实验技术对Stairmand型旋风分离器中安装减阻杆前后的强湍流场进行了测量。通过速度场、湍流强度、Reynolds应力等物理量的对比分析,表明减阻杆降低了中心涡核区的旋转动能和湍流强度。对减阻杆减阻机理进行了更深入的探讨。     

Extended CFD/DEM model for the simulation of circulating fluidized bed

The Euler–Lagrange approach combined with a deterministic collision model, so-called discrete element method, is investigated. In this work, the physical values of fluid and particle phases are determined in separated grids. The proposed procedure allows the variation of the fluid grid resolution independent of the particle size and consequently improves the calculation accuracy. A validation study has been performed to assess the results obtained from an in-house CFD/DEM code and a quasi-2D spouted–fluidized bed of Plexiglas®. The results suggest that the extended CFD/DEM model can predict accurately the particles motion and the pressure gradients in the bed. In view of the high computing cost, special emphasis is put on an effective program design such as the application of the multi-grid method and the parallel calculation. Hence, the influence of increasing the processor numbers (up to 36) on the calculation efficiency of the extended CFD/DEM model will be analysed. Finally, the improved CFD/DEM model is applied to simulate relevant engineering equipments but in small scale with relative large particles and thus less number of particles. In this context, the hydrodynamic behaviour of gas–solid flow in a 3D circulating fluidized bed with a particle separator (cyclone) will be estimated.     

Effect of the inlet angle on the performance of a cyclone separator using CFD-DEM

Hydrodynamic characteristics in a cyclone separator are simulated by means of DEM-CFD. Reynolds stress turbulence model (RSM) is used to capture gas turbulence. By changing the inlet angle, the distributions of pressure drop, tangential and axial velocity of gas phase are obtained within the cyclone. Simulated results indicate that the flow pattern consists of two regions: loss-free vortex region and forced vortex region. The negative inlet angle brings about a larger pressure drop comparing to positive inlet angle. The separation efficiency and trajectory of particles from simulation are obtained. The effects of inlet angle and particle size on separation efficiency are quantified. The separation efficiency is increased with an increase of particle size, while the separation efficiency firstly increases and then declined as inlet angle changes from negative to positive. An agreement between the numerical simulation and experimental results has been achieved in a cyclone separator.     

Gas-solid separation performance and structure optimization in 3D printed guide vane cyclone separator

Low separation efficiency and large pressure drop are two common problems of cyclones. In this paper, a 3D printed guide vane cyclone separator was designed to study the separation efficiency, turbulent kinetic energy, and particle movement of particle group by experiment and simulation. The results shown that the tangential velocity was the major influence of separating. The bottom of the exhaust pipe was the main region of gas–solid separation and pressure drop. The separation efficiency and pressure drop were positively correlated with the inlet velocity and the particle radius of the fluid. The distribution of turbulent kinetic energy that leaded to the pressure drop loss was concentrated on the inlet of the exhaust pipe. The swirl has external and internal two directions. The optimized cyclone has a longer and narrower blade flow path to obtain higher separation efficiency, especially at low inlet velocity.     

Experimental and CFD study on effects of spiral guide vanes on cyclone performance

This paper presents an experimental and numerical study on a tangential inlet cyclone separator with a spiral guide vane which is not often researched. Numerical pressure drop results were in close agreement with the experimental data. The spiral guide vane was also found to considerably influence the velocity distribution, turbulence intensity, pressure drop and collection efficiency in the cyclone. A critical value of spiral guide vane turns appeared below or above which there was a marked increase in collection efficiency, pressure drop, and tangential velocity. Compared to a cyclone with zero spiral guide vane turn, the maximal decrease in collection efficiency in the cyclone with the critical spiral guide vane turns (one turn) was 2% approximately. The maximum-efficiency inlet velocity appeared to exist independent of spiral guide vane turns, as inlet velocity affected the radial distance traveled by the rebounded particles from the inner wall. The analysis of flow field in cyclones indicated that the flow field was improved with the spiral guide vanes employed to some extent. The results presented here may provide a workable reference for the effects of spiral guide vanes on the flow field and corresponding performance in cyclone separators.     

PM2.5细颗粒物分离技术的数值模拟和性能改进

旋风切割器是分离细颗粒物的主流技术,为了提高其分离效率并减少能耗,本文分析了切割器参数对粒子分离的影响.基于计算流体动力学数值模拟的方法,分析了VSCC型旋风切割器的内部湍流流场,比较15~25L/min范围内不同流速下的涡流变化情况;基于"逃逸率"概念,模拟1~6μm内不同粒径的细小粒子逃逸率随流速的变化曲线,考察临界粒径dc并结合气溶胶实验进行验证,分析流速对分离性能的影响程度;之后考察了流速对压降的影响,提出一种几何参数改进方案,在避免压降升高的前提下提高分离性能.研究表明:流速影响旋风切割器内的湍流分布,随着流速增大,临界粒径变小,分离性能得到提升,模拟结果在16 L/min的流速下,临界粒径约为2.5μm,与实验结果基本一致,并且利用曲线给出计算总分离效率的思路;调节几何参数可以实现在低能耗的前提下,将临界粒径进一步降低为1.1μm,收集效率更高.研究结果可为PM2.5切割器的商业选择或工程设计提供理论参考.     

Effects of the prolonged vertical tube on the separation performance of a cyclone

This article aims at the gas flow into the dustbin of conventional cyclones, the prolonged cyclone (attaching a vertical tube at the bottom of the dust outlet) is proposed by some researchers, which can make flow with dust enter into the tube and separate further. The Reynolds stress transport model (RSTM) has been employed to predict the gas flow fields of the conventional and prolonged cyclones. The tangential velocity, axial velocity profiles and turbulent kinetic energy profiles are presented, and the downward flow rates into the dustbin of the three cyclones are compared. The separation performances of these three cyclones are tested. The result indicates that the tangential velocity, axial velocity and turbulent kinetic energy in the dustbin reduce greatly when the prolonged vertical tube attaching into the dust outlet, which can avoid the re-entrainment of already separated dust effectively. Furthermore, the prolonged vertical tube increases the separation space of dusts. The downward flow rate into the dustbin of the prolonged cyclone decreases compared with the conventional cyclone. The experimental results show that the prolonged vertical tube can improve the separation efficiency by a slightly increased pressure drop. However, for an even longer tube, the separation efficiency is slightly reduced. Thus, there is an optimal tube length for a given cyclone.     

Study and optimization of flow field in a novel cyclone separator with inner cylinder

This paper presents a study of gas-solid flow in a novel cyclone separator with inner cylinder, compared with that in a conventional cyclone. The Reynolds stress model (RSM) is used to simulate fluid flow, and the discrete phase model (DPM) is selected to describe the motion behavior of particles. The experimental data measured by particle image velocimetry (PIV) is used to verify the reliability of the numerical model. The results show that in the novel cyclone, the cleaned gas can be quickly discharged from the vortex finder, the movement distance and residence time of fine particles are prolonged, the short-circuit flow and vertical vortex under the vortex finder are eliminated, the mutual interference between upflow and downflow in the cylinder is eliminated, and the region of quasi-free vortex in the cone is enlarged. Compared with the conventional cyclone, the novel cyclone has higher collection efficiency and lower pressure drop.     

旋风分离器内颗粒运动阻力的特征

分析了旋风分离器内颗粒运动阻力的特性，计算了某些工况下的颗粒雷诺数，进而分析说明了在旋风分离器内固体颗粒运动的的阻力不仅有粘性力的作用，而且有体形力的作用。     

Comparison of CFD analysis to empirical data in a commercial vortex tube

This paper presents a comparison between the performance predicted by a computational fluid dynamic (CFD) model and experimental measurements taken using a commercially available vortex tube. Specifically, the measured exit temperatures into and out of the vortex tube are compared with the CFD model. The data and the model are both verified using global mass and energy balances. The CFD model is a two-dimensional (2D) steady axisymmetric model (with swirl) that utilizes both the standard and renormalization group (RNG) k-epsilon turbulence models. While CFD has been used previously to understand the fluid behavior internal to the vortex tube, it has not been applied as a predictive model of the vortex tube in order to develop a design tool that can be used with confidence over a range of operating conditions and geometries. The objective of this paper is the demonstration of the successful use of CFD in this regard, thereby providing a powerful tool that can be used to optimize vortex tube design as well as assess its utility in the context of new applications.