HYDRODYNAMIC MODEL FOR THE IMPELLER REGION IN AN AERATED AND STIRRED TANK

The radial and axial distribution of mean 1iquid velocity were measured by a.hot-filmanemometer at the impeller region in an aerated and stirred tank 0.287m in diameter.The tangentialjet model for impeller discharge flow used for single phase flow was modified to conform with thecharacteristics of gas-liquid flow.The radial and axial velocity profiles at the impeller region in thegas-liquid stirred tank were calculated by the model The results predicted by the model were in goodagreement with those obtained in experiment.     

轴向流固定床内流场的数值模拟与实验验证

The computational fluid dynamics model with porosity and drag coefficient was used to describe fluid flow in an axial flow fixed bed according to the characteristics of fluid flow in the fixed-bed of the reactor. The commercial computational fluid dynamics (CFD) code CFX was used to simulate the flow field in the axial flow fixed bed. The simulation predictions are in good agreement with experimental results of a large cold model. The influence of gas distributor on the flow field in the axial flow fixed bed was studied. A suitable gas distributor was used to attain less than 0.06 kPa radial pressure difference and less than 5.2% radial velocity difference in fixed bed.     

单喷雾射流在受限空间内的错流混合(英文)

In order to achieve uniform mixing between spray droplets and crossflow, cold-model experiment of a hollow-cone water spray in an air crossflow is investigated via a numerical simulation. The simulation cases are designed by using the orthogonal design method. The Eulerian-Lagrangian formulation is employed for modeling the droplets-crossflow two-phase flow while the realizable k-ε turbulence model is used to describe the turbulence. A new index, mixedness quality, is proposed to assess the overall mixing of the droplets in the crossflow. The simulation results demonstrate that the counter-rotating vortex pair (CVP) imposes a more significant impact on the spatial distribution than on the size distribution of the droplets. Pairs of CVP with smaller scales are preferable for achieving a better mixing. The influencing factors are listed in the following order in terms of the degree of their impact from the greatest to the least: the Sauter diameter of the initial droplets, the mixing tube diameter, the spray angle, the velocity of the inlet crossflow, and the vertical velocity of the initial droplets. A moderate droplet diameter, a smaller tube diameter, a moderate spray angle, a greater crossflow velocity and a moderate vertical velocity of the droplet are favorable for achieving a higher mixedness quality of the jet spray in a confined crossflow.     

Numerical simulation of flow focusing pattern and morphological changes in two-phase flow inside nozzle

The flow focusing nozzle is a new type of nozzle that performs effective atomization of the discrete phase by means of high-speed motion of the continuous phase.The flow pattern and its morphological changes have a significant effect on the atomization, but the influence of different parameters on the morphological change of the flow pattern remains unclear.The flow focusing pattern and morphological changes in the two-phase flow inside the nozzle were simulated numerically, based on the volume of fluid method.The results demonstrate that the ratio of the nozzle-to-capillary distance and capillary diameter, the gas–liquid velocity ratio, and capillary diameter have significant effects on the flow pattern.When the ratio of the nozzle-to-capillary distance H and capillary diameter D increases, or the capillary diameter D increases, the flow pattern tends to transform into a laminar form; however, when the gas–liquid velocity ratio V increases, the flow pattern tends to transform into a turbulence form.Furthermore, we define the cone-shaped expansion rate, cone-shaped focusing rate,and cone angle in order to study the morphological changes in the cone shape inside the nozzle.The results indicate that the morphological change of the cone shape and flow pattern transformation is interrelated.When the cone shape tends to be unstable, the flow pattern changes towards flow blurring, whereas, a stable cone indicates that the flow tends to exhibit a droplet pattern.     

基于颗粒动理学的气固喷射器流动特性三维数值模拟

A computational study on the flow behavior of a gas-solid injector by Eulerian approach was carried out. The gas phase was modeled with k-ε turbulent model and the particle phase was modeled with kinetic theory of granular flow. The simulations by Eulerian two-fluid model （TFM） were compared with the corresponding results by discrete element method （DEM） and experiments. It was showed that TFM simulated results were in reasonable agreement with the experimental and DEM simulated results. Based on TFM simulations, gas-solid flow pattern, gas velocity, particle velocity and the static pressure under different driving jet velocity, backpressure and convergent section angle were obtained. The results showed that the time average axial gas velocity sharply decreased and then slightly increased to a constant value in the horizontal conveying pipe. The time average axial particle velocity increased initially and then decreased, but in the outlet region of the convergent section the particle velocity remarkably increased once more to the maximal value. As a whole, the static pressure distribution change trends were found to be independent on driving gas velocity, backpressure and convergent section angle. However, the static pressure increased with increase of convergent section angle and gas jet velocities. The difference of static pressure to backpressure increased with increasing backpressure.     

旋流板内两相流场的CFD模拟与分析

The flow field of gas and liquid in a φ150mm rotating-stream-tray (RST) scrubber is simulated by using computational fluid dynamic (CFD) method. The simulation is based on the two-equation RNG κ-ε turbulence model, Eulerian multiphase model, mad a real-shape 3D model with a huge number of meshes. The simulation results include detailed information about velocity, pressure, volume fraction and so on. Some features of the flow field are obtained: liquid is atomized in a thin annular zone; a high velocity air zone prevents water drops at the bottom from flying towards the wall;the pressure varies sharply at the end of blades and so on. The results will be helpful for structure optimization and engineering design.     

Numerical simulation of the tube erosion resulted from particles impacts

In this paper,a tube erosion caused by the turbulent flow of a dilute particle-laden gas isstudied numerically.Eulerian equations are used to describe the gas-phase motion with the turbulenceviscosity evaluated from a k-ε model of turbulence.The effect of the turbulence with a stochasticdispersion model has been taken into account for the prediction of impact particle velocity and itstrajectory,The particle impact and rebound model and the erosion model of ductile alloys obtainedby Tabakoff et al.are used to predict the particle rebound phenomena and the erosion suffered bythe tubes.The results obtained in this study include the distributions of particle collision frequencyand erosion of tube surface.     

具有冲击平板的雾化喷雾流中汽液流动的模拟

A comprehensive three-dimensional model of droplet-gas flow was presented to study the evolution of spray in the effervescent atomization spray with an impinging plate.For gas phase,the N-S equation with the k-ε turbulence model was solved,considering two-way coupling interaction between droplets and gas phase.Dispersed droplet phase is modeled as Lagrangian entities,accounting for the physics of droplet generation from primary and secondary breakup,droplet collision and coalescence,droplet momentum and heat transfer.The mean size and statistical distribution of atomized droplets at various nozzle-to-plate distances were calculated.Some simulation results were compared well with experimental data.The results show that the existence of the impinging plate has a pronounced influence on the droplet mean size,size distribution and the droplet spatial distribution.The air-to-liquid ratio has obvious effects on the droplet size and distribution.     

Unsteady RANS and detached eddy simulation of the multiphase flow in a co-current spray drying☆

A detached eddy simulation (DES) and a k-ε-based Reynolds-averaged Navier–Stokes (RANS) calculation on the co-current spray drying chamber is presented. The DES used here is based on the Spalart–Al maras (SA) turbu-lence model, whereas the standard k-ε(SKE) was considered here for comparison purposes. Predictions of the mean axial velocity, temperature and humidity profile have been evaluated and compared with experimental measurements. The effects of the turbulence model on the predictions of the mean axial velocity, temperature and the humidity profile are most noticeable in the (highly anisotropic) spraying region. The findings suggest that DES provide a more accurate prediction (with error less than 5%) of the flow field in a spray drying chamber compared with RANS-based k-εmodels. The DES simulation also confirmed the presence of anisotropic turbulent flow in the spray dryer from the analysis of the velocity component fluctuations and turbulent structure as il us-trated by the Q-criterion.     

分级进风燃烧室内旋流反应流的湍流特性

This paper presents an experimental investigation of the turbulent reacting flow in a swirl combustor with staged air injection. The air injected into the combustor is composed of the primary swirling jet and the secondary non-swirling jet. A three dimension-laser particle dynamic analyzer （PDA） was employed to measure the instantaneous gas velocity. The probability density functions （PDF） for the instantaneous gas axial and tangential velocities at each measuring location, as well as the radial profiles of the root mean square of fluctuating gas axial and tangential velocities and the second-order moment for the fluctuating gas axial and tangential velocities are obtained. The measured results delineate the turbulence properties of the swirling reacting flow under the conditions of staged combustion.     

Mathematical modelling of a hydrocyclone for the down-hole oil–water separation (DOWS)

In this study, a mathematical model is developed to predict the efficiency of a down-hole oil–water separation hydrocyclone. In the proposed model, the separation efficiency is determined based on droplet trajectory of a single oil droplet through the continuous-phase. The droplet trajectory model is developed using a Lagrangian approach in which single droplets are traced in the continuous-phase. The droplet trajectory model uses the swirling flow of the continuous-phase to trace the oil droplets. By applying the droplet trajectory, a trial and error approach is used to determine the size of the oil droplet that reaches the reverse flow region, where they can be separated. The required input for the proposed model is hydrocyclone geometry, fluid properties, inlet droplet size distribution and operational conditions at the down hole. The model is capable of predicting the hydrocyclone hydrodynamic flow field, namely, the axial, tangential and radial velocity distributions of the continuous-phase. The model was then applied for some case studies from the field tested DOWS systems which exist in the literature. The results show that the proposed model can predict well the split ratio and separation efficiency of the hydrocyclone. Moreover, the results of the proposed model can be used as a preliminary evaluation for installing a down-hole oil–water separation hydrocyclone system in a producing well.     

基于雷诺应力模型的脱油旋流器流场特性研究

采用雷诺应力模型(RSM)对油水分离用水力旋流器进行了数值模拟,模拟出了循环流和短路流现象,得到了内部流场的轴向速度、径向速度和切向速度的分布规律;模拟结果与实验结果吻合较好,说明该湍流模型和计算方法的选取是正确的;另外,针对油相体积分数为2%,油滴粒径为40μm的混合介质进行分析,得出了油水二相的体积分数分布。在旋流器的轴心处油相体积分数最大,最大处混合介质中含油体积分数高达98.9%;在壁面附近体积分数很小,说明该水力旋流器的分离效果较好。通过数值模拟为进一步研究水力旋流器内部流场的分布和结构优化设计奠定了基础。     

导叶式旋流器内油滴的聚结破碎及影响因素

利用流场测试实验和模拟计算对导叶式旋流器的内部流场和湍流性能进行研究,得到导致旋流场中油滴发生聚结破碎现象的内因为时均速度梯度引起的黏性剪切力和湍流流动引起的高剪切应力及湍动能,并分析了油滴破碎的主要发生部位。同时为宏观考察导叶式旋流器内油滴聚结与破碎相对作用强弱,验证了旋流器的分离性能作为表征量的可行性,并在此基础上,利用导叶式旋流器的分离性能实验结果对油滴聚结破碎发生的外因进行研究,结果表明导向叶片的结构参数（叶片数和叶片出口角）和旋流器的操作参数（入口流速、溢流率、分散相入口浓度和操作温度）均会影响到油滴在旋流器中的存在和运动形态。     

Flow patterns in conical and cylindrical hydrocyclones

Using a two beam, 300 mW laser Doppler velocimeter, the tangential and axial velocity fields were determined for the water flow in a 102-mm modular hydrocyclone. The body of the equipment could be changed to transform it into a conical or a flat bottom hydrocyclone. During the tests the pressure drop and the diameter of apex and vortex were varied and the axial and the tangential velocities and their turbulence intensity were measured. The results shows that the inlet pressure affects only the magnitude of the velocities, but does not change the flow pattern. The tangential velocity is similar in both types of hydrocylones while the axial velocity is different. In both hydrocyclones the axial velocity is a function of the radial position but, while it is a linear function of the vertical coordinate in the cylindrical hydrocyclone, this is not the case for the conical vessel.     

优选结构液-液旋流管分离特性

利用库尔特粒径检测技术,对一种优选结构液-液旋流分离管的分离特性进行了较为系统的实验研究。实验测得该旋流管的临界分离粒径为30μm,而相同条件下国外典型产品,即F型旋流管的临界分离粒径为60μm,表明这种优选结构旋流管的分离特性较F型旋流管显著改善;实验结果还表明该旋流管的分离特性随处理量的增加而提高,当处理量为10m~3·h~（-1）时最好;随溢流比的加大而改善,其最佳溢流比为4％～5％;此外,还考察了为含油浓度与粒径分布之间的关系。有关结果为科学严格地评价液-液旋流分离管的分离性能提供了科学依据。     

Flow Patterns in Mini‐Hydrocyclones with Different Vortex Finder Depths

Two‐phase flow patterns in a mini‐hydrocyclone with different insertion depths of the vortex finder were measured by a phase Doppler particle analyzer. The distributions of velocity, concentration, root‐mean‐square velocity, and average diameter of particles were evaluated. A deeper insertion of the vortex finder led to smaller tangential velocity at the cross section near the column cone interface. When the vortex finder insertion depth did not reach the column cone interface, the vortex finder was inserted deeper and the line of zero velocity value migrated more distinctly inward. When the vortex finder insertion depth reached or exceeded the column cone interface, strong turbulence occurred near the vortex finder. The distributions of the axial velocities of particles and root‐mean‐square velocities indicated that circulation flow existed at the bottom part of the mini‐hydrocyclone.     

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。     

Axial symmetric flow model for a flat bottom hydrocyclone

Experiments with laser Doppler velocimetry show that, for flat bottom hydrocyclones, the axial velocity field is a function of the radius and a linear function of the axial co-ordinate, while the tangential velocity is a function of the radial co-ordinate only. Based on these results, a physical model is presented, where the flow field is divided in two zones. Zone I corresponds to the feed inlet, which occurs through a ring in the upper portion of the cylinder, the length of which depends on the length of the vortex finder tube. Zone II includes the rest of the cylinder. The axial symmetric solution of Reynolds equations for the isotropic turbulent flow leads to two sets of field equations, one for each zone in the hydrocyclone. In zone II, where experimental data were determined, simulation compares favourably with the flow pattern determined experimentally for water in a 100-mm flat bottom hydrocyclone.     

Modelling the flow in a hydrocyclone

A computational procedure is employed in the present work to predict the flow field in a hydrocyclone. Computations are carried out for turbulent flow under assumptions of axial symmetry. Turbulence closure has been affected with the help of the conventional k→ ? model that includes a new formulation of the turbulence dissipation equation. The existing formulation of the dissipation equation proved to be inadequate in predicting the true nature of the present flow field. Results of the procedure are discussed. The new model appears to predict correctly the behaviour of a conventional water-fed hydrocyclone in the absence of an air core.     

Developing a new approach for evaluating a de-oiling hydrocyclone efficiency

In this study, a new mathematical approach for evaluating of a de-oiling hydrocyclone efficiency has been developed. This new model uses the flow pattern of disperse phase and the boundary layer separation theory. In the present model unlike the other existing models, it is assumed that the droplet concentration in the radial direction is not uniform within the hydrocyclone. The hydrocyclone separation efficiency is calculated considering the droplet size distribution of the feed and the boundary layer thickness. The present approach considers the effects of droplet load, hydrocyclone geometry, mean droplet size and flow rate on the efficiency. The model is validated by comparison of the calculated separation efficiency with several previous experimental studies.