Modeling of gas-solid flow in a CFB riser based on computational particle fluid dynamics

A three-dimensional model for gas-solid flow in a circulating fluidized bed（CFB） riser was developed based on computational particle fluid dynamics（CPFD）.The model was used to simulate the gas-solid flow behavior inside a circulating fluidized bed riser operating at various superficial gas velocities and solids mass fluxes in two fluidization regimes,a dilute phase transport（DPT） regime and a fast fluidization（FF） regime.The simulation results were evaluated based on comparison with experimental data of solids velocity and holdup,obtained from non-invasive automated radioactive particle tracking and gamma-ray tomography techniques,respectively.The agreement of the predicted solids velocity and holdup with experimental data validated the CPFD model for the CFB riser.The model predicted the main features of the gas-solid flows in the two regimes;the uniform dilute phase in the DPT regime,and the coexistence of the dilute phase in the upper region and the dense phase in the lower region in the FF regime.The clustering and solids back mixing in the FF regime were stronger than those in the DPT regime.

Application of computational fluid dynamics simulation for submarine oil spill

Computational fluid dynamics （CFD） codes are being increasingly used in the simulation of submarine oil spills. This study focuses on the process of oil spills, from damaged submarine pipes, to the sea surface, using numerical models. The underwater oil spill model is developed, and a description of the governing equations is proposed, along with modifications required for the particalization of the control volume. Available experimental data were introduced to evaluate the validity of the CFD predictions, the results of which proved to be in good agreement with the experimental data. The effects of oil leak rate, leak diameter, current velocity, and oil density are investigated, by the validated CFD model, to estimate the undersea leakage time, the lateral migration distance, and surface diffusion range when the oil reaches the sea surface. Results indicate that the leakage time and lateral migration distance increase with decreasing leak rates and leak diameter, and increase with increasing current velocity and oil density. On the other hand, a large leak diameter, high density, high leak rate, or fast currents result in a greater surface diffusion range. The findings and analysis presented here will provide practical predictions of oil spills, and guidance for emergency rescues.

NUMERICAL SIMULATION BY COMPUTATIONAL FLUID DYNAMICS AND EXPERIMENTAL STUDY ON STIRRED BIOREACTOR WITH PUNCHED IMPELLER

Instantaneous flow field and temperature field of the two-phase fluid are measured by particle image velocimetry （PIV） and steady state method during the state of onflow. A turbulent two-phase fluid model of stirred bioreactor with punched impeller is established by the computational fluid dynamics （CFD）, using a rotating coordinate system and sliding mesh to describe the relative motion between impeller and baffles. The simulation and experiment results of flow and temperature field prove their warps are less than 10% and the mathematic model can well simulate the fields, which will also provide the study on optimized-design and scale-up of bioreactors with reference value.

Size dependent flow behaviors of particles in hydrocyclone based on multiphase simulation

To investigate the flow behaviors of different size particles in hydrocyclone,a designed process was numerically simulated by the transient solver,where the quartz particles possessing a size distribution were injected into a 100 mm diameter hydrocyclone with the steady water field and air core inside.A lab experimental work has validated the chosen models in simulation by comparing the classification efficiency results.The simulated process shows that the 25 μm quartz particles,close to the cut size,need much more time than the finer and coarser particles to reach the steady flow rate on the outlets of hydrocyclone.For the particles in the inner swirl,with the quartz size increasing from 5 to 25 μm,the particles take more time to enter the vortex finder.The 25 μm quartz particles move outward in the radial direction when they go up to the vortex finder,which is contrary to the quartz particles of 5 μm and 15 μm as they are closely surrounding the air core.The studies reveal that the flow behaviors of particles inside the hydrocyclone depend on the particle size.

Computational particle fluid dynamics simulation of gas–solid flow in a 3 MWth dual-circulation fluidized bed for chemical looping process

Regulation of gas–solid flow is crucial for optimizing the operation efficiency of dual-circulating fluidized beds that are considered to be the most appropriate type of chemical-looping reactors. Herein, a computational particle fluid dynamics method was employed to simulate the gas–solid flow in a 3-MWth dual-circulating fluidized bed used for chemical-looping combustion and gasification. The influence of structural difference between units on particle residence time was determined. The multi-parameter control mechanism of pressure, particle circulation, and particle residence time in a whole-loop system was investigated. Results revealed that under stable particle circulation, the particle residence time in the fuel reactor is much longer than that in the air reactor. The axial forces on the particles are reduced upon increasing particle density and size, leading to particle accumulation in the dense-phase zone. When the particle properties are stable, increasing the fluidizing gas flow rates by the same proportion leads to identical pressure drops on the involved two loop seals, which cause symmetrical alterations in the particle circulation rate between the air and fuel reactors. The dual-circulating fluidized bed exhibits certain multi-condition adaptability, which is limited by the stock bin volume. Overall, this study is beneficial for effective and economical optimization of the operation of chemical-looping dual-circulating fluidized beds.

Particle dispersion modeling in ventilated room using artificial neural network

Due to insufficiency of a platform based on experimental results for numerical simulation validation using computational fluid dynamic method(CFD) for different geometries and conditions,in this paper we propose a modeling approach based on the artificial neural network(ANN) to describe spatial distribution of the particles concentration in an indoor environment.This study was performed for a stationary flow regime.The database used to build the ANN model was deducted from bibliography literature and composed by 261 points of experimental measurement.Multilayer perceptron-type neural network(MLP-ANN) model was developed to map the relation between the input variables and the outputs.Several training algorithms were tested to give a choice of the Fletcher conjugate gradient algorithm(TrainCgf).The predictive ability of the results determined by simulation of the ANN model was compared with the results simulated by the CFD approach.The developed neural network was beneficial and easy to predict the particle dispersion curves compared to CFD model.The average absolute error given by the ANN model does not reach 5%against 18%by the Lagrangian model and 28% by the Euler drift-flux model of the CFD approach.

Effects of cartilaginous rings on airflow and particle transport through simplified and realistic models of human upper respiratory tracts

In the present study, computational fluid dynamics （CFD） is used to investigate inspiratory and expiratory airflow characteristics in the human upper respiratory tract for the purpose of identifying the probable locations of particle deposition and the wall injury. Computed tomography （CT） scan data was used to reconstruct a three dimensional respiratory tract from trachea to first generation bronchi. To compare, a simplified model of respiratory tract based on Weibel was also used in the study. The steady state results are obtained for an airflow rate of 45 L/min, corresponding to the heavy breathing condition. The velocity distribution, wall shear stress, static pressure and particle deposition are compared for inspiratory flows in simplified and realistic models and expiratory flows in realistic model only. The results show that the location of cartilaginous rings is susceptible to wall injury and local particle deposition.

Removal of SiC particles from solar grade silicon melts by imposition of high frequency magnetic field

Non-metallic particles and metallic impurities present in the feedstock affect the electrical and mechanical properties of high quality silicon which is used in critical applications such as photovoltaic solar cells and electronic devices. SiC particles strongly deteriorate the mechanical properties of photovoltaic cells and cause shunting problem. Therefore, these particles should be removed from silicon before solar cells are fabricated from this material. Separation of non-metallic particles from liquid metals by imposing an electromagnetic field was identified as an enhanced technology to produce ultra pure metals. Application of this method for removal of SiC particles from metallurgical grade silicon （MG-Si） was presented. Numerical methods based on a combination of classical models for inclusion removal and computational fluid dynamics （CFD） were developed to calculate the particle concentration and separation efficiency from the melt. In order to check efficiency of the method, several experiments were done using an induction furnace. The experimental results show that this method can be effectively applied to purifying silicon melts from the non-metallic inclusions. The results are in a good agreement with the predictions made by the model.

Study on Optimizing High-Gradient Magnetic Separation—Part 1: Improvement of Magnetic Particle Retention Based on CFD Simulations

The introduction of functionalized magnetizable particles for the purification of enzymes or for the multi-use of pre-immobilized biocatalysts offers a great potential for time and cost savings in biotechnological process design. The selective separation of the magnetizable particles is performed for example by a high-gradient magnetic separator. In this study FEM and CFD simulations of the magnetic field and the fluid flow field within a filter chamber of a magnetic separator were carried out, to find an optimal separator design. The motion of virtual magnetizable particles was calculated with a one-way coupled Lagrangian approach in order to test many geometric and parametric variations in reduced time. It was found that a flow homogenisator smoothed the fluid flow, so that the linear velocity became nearly equal over the cross section in the direction of flow. Furthermore the retention of magnetizable particles increases with a high total edge length within the filter matrix.

Stochastic neuro-swarming intelligence paradigm for the analysis of magneto-hydrodynamic Prandtl-Eyring fluid flow with diffusive magnetic layers effect over an elongated surface

In recent years,the integration of stochastic techniques,especially those based on artificial neural networks,has emerged as a pivotal advancement in the field of computational fluid dynamics.These techniques offer a powerful framework for the analysis of complex fluid flow phenomena and address the uncertainties inherent in fluid dynamics systems.Following this trend,the current investigation portrays the design and construction of an important technique named swarming optimized neuroheuristic intelligence with the competency of artificial neural networks to analyze nonlinear viscoelastic magneto-hydrodynamic Prandtl-Eyring fluid flow model,with diffusive magnetic layers effect along an extended sheet.The currently designed computational technique is established using inverse multiquadric radial basis activation function through the hybridization of a well-known global searching technique of particle swarm optimization and sequential quadratic programming,a technique capable of rapid convergence locally.The most appropriate scaling group involved transformations that are implemented on governing equations of the suggested fluidic model to convert it from a system of nonlinear partial differential equations into a dimensionless form of a third-order nonlinear ordinary differential equation.The transformed/reduced fluid flow model is solved for sundry variations of physical quantities using the designed scheme and outcomes are matched consistently with Adam's numerical technique with negligible magnitude of absolute errors and mean square errors.Moreover,it is revealed that the velocity of the fluid depreciates in the presence of a strong magnetic field effect.The efficacy of the designed solver is depicted evidently through rigorous statistical observations via exhaustive numerical experimentation of the fluidic problem.

Desulfurization characteristics of slaked lime and regulation optimization of circulating fluidized bed flue gas desulfurization process--A combined experimental and numerical simulation study

Circulating fluidized bed flue gas desulfurization(CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex flow field are two issues which have received great attention. Accordingly, a laboratory-scale fluidized bed reactor was constructed to investigate the effects of physical properties and external conditions on desulfurization performance of slaked lime, and the conclusions were tried out in an industrial-scale CFB-FGD tower. After that, a numerical model of the tower was established based on computational particle fluid dynamics(CPFD) and two-film theory. After comparison and validation with actual operation data, the effects of operating parameters on gas-solid distribution and desulfurization characteristics were investigated. The results of experiments and industrial trials showed that the use of slaked lime with a calcium hydroxide content of approximately 80% and particle size greater than 40 μm could significantly reduce the cost of desulfurizer. Simulation results showed that the flow field in the desulfurization tower was skewed under the influence of circulating ash. We obtained optimal operating conditions of 7.5 kg·s^(-1)for the atomized water flow, 70 kg·s^(-1)for circulating ash flow, and 0.56 kg·s^(-1)for slaked lime flow, with desulfurization efficiency reaching 98.19% and the exit flue gas meeting the ultraclean emission and safety requirements. All parameters selected in the simulation were based on engineering examples and had certain application reference significance.

A computational particle fluid-dynamics simulation of hydrodynamics in a three-dimensional full-loop circulating fluidized bed: Effects of particle-size distribution

A computational particle fluid-dynamics model coupled with an energy-minimization multi-scale(EMMS)drag model was applied to investigate the influence of particle-size distribution on the hydrodynamics of a three-dimensional full-loop circulating fluidized bed.Different particle systems,including one monodisperse and two polydisperse cases,were investigated.The numerical model was validated by comparing its results with the experimental axial voidage distribution and solid mass flux.The EMMS drag model had a high accuracy in the computational particle fluid-dynamics simulation of the three-dimensional full-loop circulating fluidized bed.The total number of parcels in the system(Np)influenced the axial voidage distribution in the riser,especially at the lower part of the riser.Additional numerical simulation results showed that axial segregation by size was predicted in the two polydisperse cases and the segregation size increased with an increase in the number of size classes.The axial voidage distribution at the lower portion of the riser was significantly influenced by particle-size distribution.However,radial segregation could only be correctly predicted in the upper region of the riser in the polydisperse case of three solid species.

基于CFD−DPM的空气幕协同排风罩增效除尘研究

以某机械厂打磨车间为研究对象,利用Solidworks软件建立带有空气幕协同排风罩除尘的打磨车间模型,基于气固两相流理论,采用计算流体力学离散颗粒模型(CFD−DPM)模拟分析空气幕送风速度、射流角度和射流宽度对除尘效率的影响,选取空气幕的最优参数;在此基础上,对比分析未开启排风罩、开启排风罩、同时开启排风罩与空气幕3种工况的风速分布、粉尘运移轨迹及粉尘质量浓度分布,探讨空气幕协同排风罩除尘的效果。结果表明:粉尘最大浓度、呼吸带粉尘浓度随空气幕送风速度、射流宽度的增大而减小,但不随空气幕射流角度的变化而变化;粉尘浓度随地面高度的增大先增后减,不同高度处粉尘浓度变化趋势基本一致;当空气幕射流宽度30 mm、射流角度30°、送风速度3 m/s时,通风除尘效果最佳,除尘效率高达94.2%。相比于仅开启排风罩,排风罩与空气幕协同作用下的除尘效率提高了38.8%,空气幕协同排风罩对车间除尘具有较好的增效作用。

穿流-四斜叶组合桨搅拌槽内的流场特性

基于计算流体力学(CFD)中的大涡模拟方法对穿流-四斜叶组合桨槽内流动特性进行了模拟研究,并采用粒子成像测速(PIV)技术进行了实验验证。研究了不同转速、离底距和桨叶开孔直径对流场的影响。结果表明,转速的增加可以提升下桨叶的轴流作用进而增强流场的混合效果,但转速过高会使流场内流型变得混乱,模拟结果显示较优转速为N=100r/min;离底距的增加会改善槽内顶部区域的速度分布,当离底距与液位高度比为0.29时,流场内形成了有利于混合的涡旋,搅拌槽顶部及下层区域流场速度分布合理,为较优的离底距;穿流孔径主要影响两桨叶之间的连接流,当穿流孔径为4mm时,搅拌槽内的连接流更稳定,整体高速区面积分布更为合理,能促进搅拌槽内整体的循环效果。研究结果可为穿流-四斜叶组合桨的实际工业生产应用提供数据参考。

Particle Image Velocimetry Experimental and Computational Investigation of a Blood Pump

Blood pumps have been adopted to treat heart failure over the past decades. A novel blood pump adopting the rotor with splitter blades and tandem cascade stator was developed recently. A particle image velocimetry （P1V） experiment was carried out to verify the design of the blood pump based on computational fluid dynamics （CFD） and further analyze the flow properties in the rotor and stator. The original sized pump model with an acrylic housing and an experiment loop were constructed to perform the optical measurement. The PIV testing was carried out at the rotational speed of 6952±50 r/rain with the flow rate of 3.1 l/rain and at 8186±50 r/min with 3.5 l/rain, respectively. The velocity and the Reynolds shear stress distributions were investigated by PIV and CFD, and the comparisons between them will be helpful for the future blood pump design.

About One Discrete Mathematical Model of Perfect Fluid

In work, it is constructed a discrete mathematical model of motion of a perfect fluid. The fluid is represented as an ensemble of identical so-called liquid particles, which are in the form of extended geometrical objects: circles and spheres for two-dimensional and three-dimensional cases, respectively. The mechanism of interaction between the liquid particles on a binary level and on the level of the n-cluster is formulated. This mechanism has previously been found by the author as part of the mathematical modeling of turbulent fluid motion. In the turbulence model was derived and investigated the potential interaction of pairs of liquid particles, which contained a singularity of the branch point. Exactly, this is possible to build in this article discrete stochastic-deterministic model of an ideal fluid. The results of computational experiment to simulate various kinds of flows in two-dimensional and three-dimensional ensembles of liquid particles are presented. Modeling was carried out in the areas of quadratic or cubic form. On boundary of a region satisfies the condition of elastic reflection liquid particles. The flows with spontaneous separation of particles in a region, various kinds of eddy streams, with the quite unexpected statistical properties of an ensemble of particles characteristic for the Fermi-Pasta-Ulam effect were found. We build and study the flow in which the velocity of the particles is calibrated. It was possible using the appropriate flows of liquid particles of the ensemble to demonstrate the possibility to reproduce any prescribed image by manipulating the parameters of the interaction. Calculations of the flows were performed with using MATLAB software package according to the algorithms presented in this article.

低负荷下CFB锅炉二次风优化对NO_(x)排放影响的数值模拟

为控制循环流化床(circulating fluidized bed,CFB)锅炉低负荷下NO_(x)的原始排放,以某350 MW超临界CFB锅炉为研究对象,基于计算颗粒流体力学(computational particle fluid dynamics,CPFD)方法对40%负荷下燃烧过程进行数值模拟。分析了不同二次风角度、新增二次风量对NO_(x)排放的影响。结果表明:随着射流角度的减小,炉膛出口NO浓度逐渐降低,CO浓度无明显增加。部分二次风上移后炉膛密相区氧浓度降低,不完全燃烧增加,还原性氛围增强,抑制了NO的生成。当新增风量从10%增加到30%时,NO排放浓度降低了17.2%。但随着比例的进一步提高,炉膛密相区的缺氧环境造成燃烧效率下降,温度大幅降低。因此,在不影响燃烧的前提下可以通过提高新增二次风比例来降低NO的原始排放浓度。

液压过滤器内的颗粒迁移数值模拟

过滤技术广泛应用于化工过程、燃油和液压领域。在液压系统中,过滤器也是重要的元件之一。与针对过滤的结构设计和滤芯选材研究相比,颗粒污染物迁移是影响过滤器性能的基础因素,需要加以重视。由于颗粒污染物的尺寸较小且数量巨大,在数值模拟中完全追踪每一个颗粒难度较大。因此,以某一液压过滤器为例,采用计算流体动力学-离散相(CFD-DPM)耦合的方法,对过滤过程中颗粒污染物的迁移规律进行初步探讨,尤其是流量和油温对颗粒迁移的影响。结果表明,入口油液速度对过滤的快慢影响较大,但对于过滤效率影响较小。相比之下,油液温度在0.3 s内对颗粒的瞬态阻拦影响较大,但对于稳态的影响也较小。

多流程循环流化床气固流动和燃烧的计算颗粒流体力学数值模拟

多流程循环流化床与传统流化床相比,能有效降低炉膛高度,实现小型化。以多流程循环流化床锅炉为研究对象,基于计算颗粒流体力学,对气固流动和燃烧过程进行了数值模拟,计算结果与中试装置结果吻合较好。结果表明:炉膛内颗粒相浓度由高到低依次为主燃烧室、副燃烧室、燃尽室,炉内颗粒分布呈现“环-核”结构;炉膛温度范围为1 000~1 200 K,主燃烧室的温度大于副燃烧室,副燃烧室的温度大于燃尽室与旋风分离器;增大一、二次风的配比使炉膛密相区的氧气含量增大,加剧了燃烧,使床温升高;由副燃烧室进行分级给料,有利于焦炭还原NO,使出口NO浓度明显下降,有利于减少氮氧化物的排放。

CFB锅炉宽筛分颗粒临界流化风速研究

基于计算颗粒流体力学(CPFD),通过表征常规CFB锅炉床料(Set 1)、增加炉内细颗粒含量(Set 2)和减小初始床支撑料粒度(Set 3) 3种筛分分布的SiO_(2)颗粒,研究颗粒筛分变化对临界流化风速的影响。研究结果表明:在相同床层高度下,Set 1、Set 2和Set 3床料的临界流化风速分别为0.51、0.30和0.20 m/s。表明增加炉内细颗粒含量和减小初始床支撑料粒度均可明显降低临界流化风速。将宽筛分颗粒临界流化风速的数值模拟结果与相关关联式预测结果进行对比,表明ERGUN关联式的预测结果偏差较小,WEN-YU关联式的预测结果明显偏低。