应用数值模拟方法对旋流器空气柱特性的探讨

利用数值模拟结果对空气柱内的速度分布特征、压力分布特征、空气柱大小及其影响因素等方面进行了讨论。结果表明,空气柱具有强制涡的特点,且在轴向方向存在压力梯度,由于流场的不稳定性导致空气柱的大小和位置不断发生变化,造成不对称流场出现,从而降低了旋流器的分离效率。     

Experimental study on the air core in a hydrocyclone

The evolution of an air core is an important phenomenon in hydrocyclones, which are sensitive to the operating conditions. The morphology of the air core in a hydrocyclone is studied experimentally, using a high-speed video camera and a noise analyzer. Three stages are observed during the increase of flow rate from 300 to 2,400 L per hour, which could be separated by both the noise measurement and the stability of the air core. The flow rate is found to have a nonmonotonic effect on the diameter of the air core, leading to a peak diameter. The influence of the overflow and underflow on the underflow-to-throughput ratio and air flow patterns is also investigated. It is found that the underflow-to-throughput ratio and air flow patterns are sensitive to the valve openings of both outlets.     

Improvement of performance efficiency of a hydrocyclone with design modification by suppressing air core

Hydrocyclones have been used for beneficiation of coal and mineral in coal washeries and mineral process industries. To enhance the efficiency of hydrocyclone, it is very essential to quantify the presence or absence of air core within the hydrocyclone. In the present study, for the first time, a new hydrocyclone design has been conceptualized and tested for its efficiency in separation of particles based on gravity. Experimental investigations have been carried out using design of experiments and the results have been analyzed statistically. The results have shown that suppressing the air core improves the separation efficiency of the hydrocyclone. Efforts have been made to explain the concept through fundamentals of fluid flow in hydrocyclone. The air core has a significant effect on particle separation as the relative density of the particles approach to the fluid density. The results will be used in the development of a new design of dense medium hydrocyclone at industrial scale that will improve the separation efficiency of the hydrocyclones by separating the near gravity particles more efficiently.     

The influence of apex diameter on the pattern of solid/liquid ratio distribution within a hydrocyclone

Knowledge of the pattern of solid/liquid ratio distribution within a hydrocyclone is very important for reliable design and efficient operation. This pattern was examined using a 100mm hydrocyclone for a wide range of apex diameters at high solid contents of the feed pulp. The measurements were taken along orbit radii at several horizontal level positions along the cyclone length. The results give a complete pattern of pulp-solid content distribution for the studied parameters. An empirical equation relating the pulp solid/liquid ratio with all the studied variables was established. The predicted data show good agreement with the experimental results.     

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.     

Identification and prediction of air core diameter in a hydrocyclone by a novel online sensor based on digital signal processing technique

A hydrocyclone is a particle separation device widely used in chemical and allied process industries in which a particle-fluid mixture is injected tangentially creating a strong swirling, recirculation flow. The particle separation efficiency increases by suppressing the air core, so online prediction of air core formation has significant importance in the industrial operations. Performance of hydrocyclone is greatly influenced by shape and size of air core. A novel type of senor technique has been developed to identify and predict the air core diameter from online live data using data acquisition card. The true signal amplitudes change as a function of the time was used with noise interruption for random changes in amplitude. Noises are eliminated by using moving average technique. The slope of the curve is continuously tracked to determine sudden or abrupt change and indicates the formation of air core. It has been observed that a strong air core of diameter 0.95 cm to 1.2 cm was formed during experimentation and matched with predicted values over an entire flow regime. The experimental and finally an alarm is designed which gives alerts once air core is formed and calculates air core diameter. For calculating air core diameter a polynomial equation is fitted between pressure difference and the pressure transmitter reading. A simple moving average with a smooth width of 10 was used for prediction of air core. Experimental results indicate that the digital signal sensor techniques identify the air core and measure air core diameter very accurately and can be used in many mining and mineral based chemical and allied process industries.     

喷射式环流反应器内流速分布的实验研究

主要研究了喷嘴位置和喷嘴出口速度对底部是圆锥台的喷射环流反应器(JLR)的影响,从而确定最优出口速度和喷嘴位置。对JLR内部流速进行测量,绘出JLR内的速度分布图,并从速度场和内外循环比2个方面进行分析,从而确定最优参数。结果表明:在实验室范围内,当喷嘴出口速度为2.1 m/s,喷嘴位置为40 mm时较优。导流筒内速度呈抛物线分布;喷嘴出口速度增加,环隙速度对应增大,内外循环比也增加;随着喷嘴位置逐渐靠近导流筒,内外循环比先增加,再减小。     

Prediction of strongly swirling flow within an axial hydrocyclone using two commercial CFD codes

Two commercial CFD codes were used to simulate the strongly swirling single-phase flow with core recirculation within an axial hydrocyclone. Both packages used a Differential Reynolds Stress Model with default constants for the turbulence closure. The effect of omitting wall reflection terms was also investigated and it was generally found that this lead to better agreement with experiment. Interestingly, the predicted velocity profiles from the two CFD codes did not agree with each other. Possible reasons for this are different turbulence modelling approaches with different terms for the turbulent diffusion and rapid pressure-strain terms.     

The distribution of lamellar lengths within a spherulite

One of the problems to be considered in the application of the Halpin-Kardos theory to crystalline polymers is the relation of the crystal length to the only related and measurable parameter, spherulite size. The number average crystal length has been computed for various two and three dimensional models for the crystallization process assuming heterogeneous nucleation. It was found that high values of crystallinity are consistent only with lamellae that are stacked in a parallel fashion. For these systems the number average lamellar length is 0.55 of the spherulite radius. Lower crystallinity polymers have an average lamellar length 0.3 to 0.5 of the spherulite radius, the actual value being determined by the radius. For spherulites of radius 1μm or greater, the size of the primary nucleus has no noticeable influence on the average lamellar length.     

分级旋流器的分选作用

以两次技术检查数据为基础 ,对太原选煤厂粗煤泥回收流程中 3组分级旋流器底流与溢流的灰分差进行了分析归纳 ,确认分级旋流器对 0 0 4 5～ 0 2 5mm粒级有较明显的按密度分选作用 ;同时对影响因素进行了简单分析 ,提出了初步的改进方案     

Radial liquid velocity distribution in an external-loop airlift column with a tapered riser

Radial and axial liquid velocity distributions in the tapered riser were investigated theoretically and experimentally. The liquid velocity distributions were computed by solving the Navier-Stokes equation numerically based on a modified mixing-length theory. Both radial and axial components of liquid velocity were taken into account. As a result, we found that the radial velocity component was much smaller than the axial velocity component. For a cylindrical column, which means no tapered section, a simplified solution was obtained. The simplified solution was found to agree well with the rigorous numerical solution even in the tapered riser. To confirm the validity of the present hydrodynamic model, the velocity distributions in the tapered riser were measured by an electric probe method using KCl solution as a tracer. The measured velocity distributions agreed with the computed ones, except in the vicinity of the bottom of the tapered riser at high gas flow rates.     

Experimental deep-channel velocity profiles and operating characteristics for a single-screw extruder

Data have been obtained on the operation of a deep-channel single-screw extruder, pumping a Newtonian liquid under isothermal, developed flow conditions. Flow rate, screw speed, and pressure gradient characteristics were measured, and a tracer particle technique was employed to determine channel velocity profiles. The data were required for the testing and development of a computer model for flow in the extruder, which takes into consideration channel curvature. Results confirm the correctness of the computer solutions previously reported.     

LDV measurements of particle velocity distribution in an annular stripper

Particle descent velocities in an annular stripper were measured by a laser Doppler velocimetry (LDV) system. In the radial direction, particle descent velocity was relatively constant in the mid-region of the stripper and increased towards the walls on both sides, exhibiting an anti-U-shaped distribution. Particle descent velocity in the radial mid-region increased with the increase of superficial gas velocity, and the maximum in the outer wall region increased significantly with the increase of solid mass flux. Superficial stripping gas velocity had stronger effect on particle velocity distributions near the stripper gas distributor, and such effect weakened with the increase of the distance from the distributor. Local particle velocity and its radial profiles could be adjusted by changing the superficial stripping gas velocity. Empirical formulas were established to describe the relationships between the local particle velocity and cross-sectional averaged velocity based on the effects of operating conditions and measuring positions. The result showed that the predicted data was in good agreement with the experimental value.     

The hydrodynamics of a hydrocyclone based on a three-dimensional multi-continuum model

The concept and principles of applying a multi-continuum model for calculating a hydrocyclone performance is presented. In this model the carrying liquid is described as one continuum, and each particle fraction, with its characteristic size is described as a separate continuum. Particle–particle and particle–fluid interactions derived from a lubrication theory and a collision theory are discussed. A set of governing partial differential equations consisting of mass and momentum conservation equations together with constitutive expressions is discussed. These equations were discretized by applying an unstructured grid consisting of tetrahedral elements. A numerical solver based on a finite element method combined with a segregated approach is described. The numerical approach is subject to ongoing research.     

An investigation into hydrodynamics of a hydrocyclone with an additional double-jet injector

Results of the measurement of flow rate characteristics and of air column size in a hydrocyclone equipped with a special nozzle used for additional injection of water into the apparatus for the purpose of controlling parameters of hydraulic classification are presented. It was found that additional injection of water considerably alters the hydrodynamic situation in the apparatus. Dependence of changes in the flow rate of water through overflow and underflow nozzles on a direction of injection and flow rate of injected water was established. Explanations for mechanisms of the effect of radially and tangentially directed injection on characteristics of particle size classification are proposed.     

旋流器对电脱盐装置含油污水的处理

介绍了旋流器在炼油厂电脱盐装置污水处理系统中的工艺流程。经旋流器处理,电脱盐装置排出污水的含油量可稳定降低到150mg/L以下,实现了装置排出污水分级达标管理的目标。     

The aspiration efficiency of a tube sampler operating in a slow moving air stream facing vertically upwards

The aspiration efficiency of a thin-walled, cylindrical aerosol sampler facing vertically upwards in a slow moving vertical air stream is numerically investigated using both a potential flow model and a viscous flow model. In order to predict the air flow around the sampler, for the potential flow model we use a boundary element method whereas for the viscous flow model we use a control volume method. The motion of the particles is then predicted by considering both the drag and gravitational forces. We have found that both numerical models produce similar predictions for the aspiration efficiency and the predictions reveal a more complex sampling behaviour when the sampler is operated in a slow moving air environment, where the air velocity is comparable with the magnitude of the particle settling velocity, than for faster moving air flows. The comparison of the numerical predictions with the only available experimental data indicates that the aspiration efficiency is in qualitative agreement but further investigations are required in order to fully reveal all the sampling characteristics in slow air flows.