Visualization of the Precessing Vortex Core in a Cyclone Separator by PIV

The precessing vortex core (PVC) in a cyclone separator plays an important role in the separation performance and in further understanding of the general law of periodic unsteady flow therein. In this paper, the unsteady flow field is investigated with particle image velocimetry (PIV), and the instantaneous velocity, vorticity, tangential velocity, and radial velocity are acquired by analyzing the images of instantaneous flow. It is for the first time reported that there is a centrifugal flow region close to the dust discharge zone and its maximum value is higher than the mean radial velocity. This discovery is very important for understanding the principle of separation of particles in the area of dust discharge. Determination of the frequency and amplitude of PVC was conducted in the region where the phenomenon of PVC is remarkable. Results agree well with those obtained by hot wire anemometry. The observations of the center of vortex core and the bimodal distribution of the amplitude of the PVC indicate the vortex core precesses around the geometric axis of the cyclone in its own way.

Numerical Simulation of Particle Concentration in a Gas Cyclone Separator

The particle concentration inside a cyclone separator at different operation parameters was simulated with the FLUENT software. The Advanced Reynolds Stress Model （ARSM） was used in gas phase turbulence modeling. Stochastic Particle Tracking Model （SPTM） and the Particle-Source-In-Cell （PSIC） method were adopted for particles computing. The interaction between particles and the gas phase was also taken into account. The numerical simulation results were in agreement with the experimental data. The simulation revealed that an unsteady spiral dust strand appeared near the cyclone wall and a non-axi-symmetrical dust ring appeared in the annular space and under the cover plate of the cyclone. There were two regions in the radial particle concentration distribution, in which particle concentration was low in the inner region （r/R≤0.75） and increased greatly in the outer region （r/R〉0.75）. Large particles generally had higher concentration in the near-wall region and small particles had higher concentration in the inner swirling flow region. The axial distribution of particle concentration in the inner swirling flow （r/R≤0.3） region showed that there existed serious fine particle entrainment within the height of 0.SD above the dust discharge port and a short-cut flow at a distance of about 0.25D below the entrance of the vortex finder. The dimensionless concentration in the high-concentration region increased obviously in the upper part of the cyclone separation space when inlet particle loading was large. With increasing gas temperature, the particle separation ability of the cyclone was obviously weakened.

A new technique of combining accretion by cyclone separator and scattertube for tailings dams

A new technique of combining accretion by cyclone separator and scattertube for tailings dams was developed according to laboratory experiment, model experiment and spot experiment technology. Three tailings dams were successfully constructed by the new technique. The results of engineering geological exploration, static and dynamic test and stability analysis on Baizhishan tailings dams prove that the new technique improves structure and stability of the dams and working conditions compared with the traditional technique. The thin layers of fine-grained soils are greatly reduced, fine tailings sand is solid to make the dam stable and seepage conditions are well improved; the immersing line of the dam descends. In addition, the stability and liquefaction resistance of tailings dams are strengthened remarkably. The interior stress is compressive stress, stress level of every element is less than 1.0 and safety coefficient of every element is greater than 1.0. The safety coefficient against liquefaction of every element of tailings dams is greater than 1.5 according to the analysis of seismic response by finite element method.

Analysis of the nutation and precession of the vortex core and the influence of operating parameters in a cyclone separator

Vortices motion in the anisotropic turbulent flow of cyclones makes a vital impact on flow stability and collection performance.Nevertheless,there remains a lack of clarity in the overall feature of vortices motion.In this work,a numerical analysis was conducted to clarify the complex motion of the vortex core in a cyclone separator.The validity of the numerical model was demonstrated by comparing the computational results with experimental data in the literature.As revealed by the results,the vortex core not only has a precession motion about the geometrical center axis but also does a nutation motion in the axial direction.The frequencies of the precession motions show two main peaks.And the magnitudes of the precession and nutation motions have non-uniform distributions in the cyclone.Moreover,the precession-nutation motions of the vortex cores exhibit a similar fluctuant pattern to the dust ring on the separator wall.The inlet gas velocity and the inlet solid loading show vital effects on the magnitudes and frequencies of precession and nutation motion.

Numerical analysis on the influence of vortex motion in a reverse Stairmand cyclone separator by using LES model

This study aims to analyze the influence of vortex motion in a reverse Stairmand cyclone separator by using LES model.The mathematical analysis indicated that the energy dissipation and the flow characteristics of incompressible fluid are directly related to on the vortex motion.The results of the Q criterion-based iso-vortex surface could well reflect the tendency of the vortex structure,in which the iso-vortex surface exhibited a distorted distribution rather than around the center axis.At the turning point of velocity vector,vortices were formed and developed,and the point was the center of the local vortex core.In addition,the vortex formed an irregular annular region around the wall at the bottom of vortex finder.The vortex structure near the dust hopper presented a strong distortion.Moreover,there were two rotating flow in the opposite direction within the dust hopper.These phenomena would affect the separation performance,which was significance to cyclone separator.

Numerical investigation on dynamic characteristics of flow field in cyclone separators with different dust hopper structures

The dynamic characteristics of flow field in cyclone separators with different dust hopper structures were studied by coupling Reynolds Stress Model(RSM)and Lagrangian Particle Tracking(LPT)methods.The characteristic frequencies of cylinder section,cone section and dust hopper were calculated as f_(1)=53 Hz,f_(2)=65 Hz,and f_(3)=8 Hz by using Fast Fourier Transform(FFT)method,respectively.Based on the effects of f3 on the motion of vortex,the separated space was divided into none affected region,weakly affected region,and strongly affected region.The characteristic frequency of dust hopper increased with the decrease of dust hopper diameter,while it was independent of the height.The dust hopper with d=1.5D(model D3)and h=1.5D(model H3)can significantly decrease the effect of back-mixing on the motion of inner vortex,which is beneficial to improve the efficiency of cyclone separator.

Experimental investigation on separation characteristics of axial cyclone separator

Axial cyclone separator has been widely applied in chemical production as an efficient gas-liquid separation device.In this study,a new axial cyclone separator with integrated swirler and exhaust pipe is designed to achieve the development goal of compact structure for advanced engine,and the distribution characteristics of swirling flow patterns as well as the variation in separation characteristics are investigated under slug flow pattern.Based on flow visualizations and fluctuation characteristics of pressure signals,three typical flow patterns,namely,slug flow,swirling intermittent flow,and swirling annular flow,in the horizontal swirling separation flow are characterized.It is investigated how the inlet conditions affect the separation characteristic parameters.The separation purity and extreme points of the air separation efficiency are independent of the inlet liquid flow rate.The separation pressure drop is quadratically related to the inlet air flow rate.Based on the drift-flux model and other methods,the prediction methods for the air separation efficiency and pressure drop are proposed,and the prediction accuracy is within±20%,which may provide instructions for the practical application of axial cyclone separator.

Effects of working parameters on the performance of cyclone separator for rapeseed combine harvester based on CFD

Existing development for cyclone separation cleaning components of the rapeseed combine harvester,which employs the suspending airflow to separate the rapeseeds from the materials other than grain(MOG),has the challenge to figure out the optimal working parameters,highlighting a need for exploration of the invisible airflow based on Computational Fluid Dynamics(CFD).The airflow status was mainly affected by the air velocities of the inlet,and the outlet for the MOG.The single factor and response surface experiments were carried out.It could be found that the inlet and MOG outlet velocities affected the air velocities through the change in the air quantity.Furthermore,the mathematical model of the relationship between the air velocities inside the cyclone and the working parameters was built,and the optimal combination of working parameters was obtained by multi-objective optimization.The inlet and outlet velocities of the optimal combination were 4.25 m/s and 29.87 m/s,respectively.Under this condition,the cleaning ratio and loss ratio of the cleaning device was 94.62%and 5.39%,respectively,as validated by the field experiment.The findings provide references for the improvement of cleaning systems for rapeseed combine harvesters.

Pressure Drop in Cyclone Separator at High Pressure

For the design of pressurized circulating fluidized beds, experiments were conducted in a small cyclone with 120 mm in diameter and 300 mm in height at high pressures and at atmospheric temperatures. Influence of air leakage from the stand pipe into the cyclone was specially focused. A semi-empirical model was developed for the prediction of the pressure drop of the cyclone separator at different operate pressures with the effect of air leakage and inlet solid loading. The operate pressure, air leakage and inlet solid loading act as significant roles in cyclone pressure drop. The pressure drop increases with the increasing of pressure and decreases with the increasing of the flow rate of air leakage from the standpipe and with the increasing of the inlet solid loading.

A PARTITIONING PARALLEL PROCEDURE FOR NUMERICAL SIMULATION OF GAS FLOW IN A CYCLONE SEPARATOR

Based on the SIMPLE-C algori thm and the non-overlapping Domain Decomposition Method (DDM), in which the Dirichlet-N eumann alternative algorithm is employed, a partitioning parallel procedure was developed to numerically simulate fluid flow in complex 3-D domains. It can well remove the limitation of speed and capacity of personal computer on large-scale numerical simulation of complex 3-D domains. In this paper, the 3-D turbulent swirling gas flow in cyclone separator was simulated. In view of the physica l reality, the computational results are bascally reasonable.

Numerical Study on Particle Motions in Swirling Flows in a Cyclone Separator

The purpose of this study is to establish the high-accurate prediction method of particle separation in a cyclone separator. Numerical simulation of the swirling flows in a cyclone separator is performed by using a large eddy simulation （LES） based on a Smagorinsky model. The validity of the simulation and the complicated flow characteristics are discussed by comparison with experimental results. Moreover, particle motions are treated by a Lagrangian method and are calculated with a one-way method. A performance for particle separation is predicted from the results of the particle tracing. As results of our investigation, the influences of the inserted height of the outlet pipe on the performance for particle separation of cyclone separator are shown.

Numerical simulation of a dense solid particle flow inside a cyclone separator using the hybrid Euler-Lagrange approach

This paper presents a numerical simulation of the flow inside a cyclone separator at high particle loads. The gas and gas–particle flows were analyzed using a commercial computational fluid dynamics code. The turbulence effects inside the separator were modeled using the Reynolds stress model. The two phase gas–solid particles flow was modeled using a hybrid Euler–Lagrange approach, which accounts for the four-way coupling between phases. The simulations were performed for three inlet velocities of the gaseous phase and several cyclone mass particle loadings. Moreover, the influences of several submodel parameters on the calculated results were investigated. The obtained results were compared against experimental data collected at the in-house experimental rig. The cyclone pressure drop evaluated numerically underpredicts the measured values. The possible reason of this discrepancies was disused.

Improving advantages and reducing risks in increasing cyclone height via an apex cone to grasp vortex end

For a cyclone, it is possible to improve separation efficiency and reduce pressure drop by increasing the cyclone height. However, an exceeded height increase could result in a dramatical drop in separation efficiency. In this study, experimental and computational fluid dynamics simulation results exhibit that the introduction of an apex cone at the dust outlet could avoid the risk of separation efficiency drop but lead to a continuous reducing of the pressure drop. Generally, the optimal cyclone height should be closely related to the natural vortex length. While, when the vortex end contracts into the separation space in the cyclone with an exceeded height, severe back-mixing of particles always occurs, which will result in the decrease of separation efficiency. Herein, it is found that when an apex cone is installed at the dust outlet, the vortex end can be grasped by the cone so as to weaken the back-mixing of particles.Meanwhile, the introduction of this apex cone can enhance the secondary separation to capture the back-mixed particles again so as to protect the efficiency. In addition, it is found that the enhanced secondary separation could come from either the stagnant current of axial velocity in the center or the improved tangential velocity of inner vortex whereas the forcibly extending the length of vortex to exceed its natural length will not significantly increase efficiency.

Modeling the gas flow in a cyclone separator at different temperature and pressure

The gas flow field in a cyclone separator,operated within a temperature range of 293 K-1373 K and a pressure range of 0.1-6.5 MPa,has been simulated using a modified Reynolds-stress model(RSM)on commercial software platform FLUENT 6.1.The computational results show that the temperature and pressure significantly influence the gas velocity vectors,especially on their tangential component,in the cyclone.The tangential velocity decreases with an increase in temperature and increases with an increase in pressure.This tendency of the decrease or increase,however,reduces gradually when the temperature is above 1000 K or the pressure goes beyond 1.0 MPa.The temperature and pressure have a relatively weak influence on the axial velocity profiles.The outer downward flow rate increases with a temperature increase,whereas it decreases with a pressure increase.The centripetal radial velocity is strong in the region of 0-0.25D below the vortex finder entrance,which is named as a short-cut flow zone in this study.Based on the simulation results,a set of correlations was developed to calculate the combined effects of temperature and pressure on the tangential velocity,the downward flow rate in the cyclone and the centripetal radial velocity in the short-cut flow region underneath the vortex finder.

CFD numerical simulation of flow velocity characteristics of hydrocyclone

A CFD based numerical simulation of flow velocity of hydrocyclone was conducted with different structural and operational parameters to investigate its distribution characteristics and influencing mechanism. The results show there exist several unsymmetrical envelopes of equal vertical velocities in both upward inner flows and downward outer flows in the hydrocyclone, and the cone angle and apex diameter have remarkable influence on the vertical location of the cone bottom of the envelope of zero vertical velocity. It is also found that the tangential velocity isolines exist in the horizontal planes located in the effective separation region of hydrocyclone. The increase of feed pressure has almost no effect on the distribution characteristics of both vertical velocity and tangential velocity in hydrocyclone, but the magnitude and gradient of tangential velocity are increased obviously to make the motion velocity of high density particles to the wall increased and to make the cyclonic separation effect improved.

Experimental Research on Enhanced Cyclone Separation of Acoustic Agglomerated Particles

To test the particles solidity and to verify the separating efficiency at normal atmospheric temperature, the experimental research was made on the enhanced cyclone separation of acoustic agglomerated fly ash particles. The separating efficiency has increased by 3%-4% in a sound field with 150 dB pressure level compared with that obtained without acoustic wave processing. The enhanced cyclone separation test study for acoustic agglomerated particles has provided a technical basis for pressurized fluid bed combustion(PFBC) application.

Application of Electrical Capacitance Tomography to the Concentration Measurement in a Cyclone Dipleg

Accurate solid concentration measurement plays a key role in the process industry. Measurements analyzed offline can be used to estimate process efficiencies, to identify problems in a flow, and to validate computational models. Online measurements can be used for active control. Electrical capacitance tomography （ECT） is a unique measuring technique with great potential in multiphase flow measurement. Experimental studies are carried out on a solid concentration measurement in a cyclone separator dipleg, using ECT. In this experiment eight electrodes are selected for the ECT sensor that is placed on the straight tube of the dipleg. The fluctuating characteristics according to the screw feeder and the effect of the airflow rate from the top of the cyclone are analyzed. The feasibility andreliability of the method are verified by the experimental results.

Structural Optimization of a Novel Up-run Gas-solid Separator

A new gas-solid separator dedicated to heavy-oil fast pyrolysis process incorporating inertial and centrifugal separation was designed. Gas and typical fluid catalytic cracking （FCC） catalyst particles （with a density of 1500 kg/m3, and a mean diameter of 45.81 p.m） were used in the study. The inlet gas velocity was kept constant at 13.36 m/s, while the solid loading at the inlet ranged from 0 to 700 g/m3. When the exhaust pipe opening was provided with two narrow-width slots near the inlet without baffles, the solid collection efficiency increased with an increasing solid loading at the inlet and was close to 95% along with a decreasing pressure drop. After increasing the secondary separation structure, the separation efficiency greatly improved. By adjusting the diameter of the secondary exhaust pipe, the separation efficiency and pressure drop could be balanced. Under the experimental conditions, when the diameter of the second exhaust pipe was equal to d=100 mm, the pressure drop was lower than 1400 Pa while the separation efficiency could exceed 99.50%; and when the diameter was equal to d=120 mm, the pressure drop was less than 700 Pa, with the separation efficiency reaching over 99.00%.

STUDY ON THE CHARACTERISTICS OF AGGLOMERATION AND CYCLONE SEPARATION OF DIESEL PARTICULATE

A particulate separation system that can be used to study the characteristics of the diesel particulate agglomeration and cyclone separation is developed It includes a diesel particulate agglomerator and a cyclone separator mainly A preliminary investigation on the cyclone separation tech nology for controlling the exhaust particulate from a diesel engine is conducted The experimental results show that the diameter distribution of the diesel particulate is changed after they pass through the agglomerator,almost 30%～40% o f the particulate agglomerated from less than 1.0μm to larger than 1.0μm ,this change contributes to trap diesel particulate With this system installed on the exhaust pipe of a single cylinder engine,the particulate separation efficiency is around 40%～60% under typical engine running condition The back pressure of this system is less than 5 kPa on full load condition,much less than that of other methods of particulate filtration This technology has the possibility to open a new prospect for particulate reduction because of its simplicity,reliability and low resistance.

Parameter matching and experiment of the combined cyclone separation and cylinder sieve cleaning system for rape combine harvester

Existing rape combine harvester with a cyclone separation cleaning device has the challenge that the loss rate and the cleaning rate increase and decrease simultaneously.A cleaning process route was proposed,which involves the cyclone separation cleaning device removing light and tiny impurities,and the cylinder sieve device removing coarse and long impurities such as pod shells and short stems.A novel cleaning system combining the cyclone separation cleaning device and cylinder sieve cleaning devices was designed.The ranges of the structure and operation parameters for each component were analyzed based on kinematics and dynamic analysis.A four-factor five-level quadratic orthogonal test was carried out,in which the loss rate and cleaning rate were taken as the evaluation indexes.The velocity at the suction port,the rotation speed of the cylinder sieve,the screw pitch of the spiral blade and the diameter of the sieve hole were taken as the influencing factors.The orthogonal test results showed that the cleaning system performed best at a rotation speed of the winnower is 600 r/min,an airflow velocity at the suction port is 18.25 m/s,a rotation speed of the cylinder sieve is 87 r/min,a screw pitch of the spiral blade is 440 mm and a diameter of the sieve hole is 4.48 mm.At this time,the loss rate of the cleaning system is 3.22%,and the cleaning rate is 95.67%.Compared to the conventional cyclone separation cleaning device,the loss rate is reduced by 2.17%and the cleaning rate is increased by 1.05%.This study can provide a reference for the optimal cleaning system design for rape combine harvesters.