Computational fluid dynamics-discrete element method simulation of stirred tank reactor for graphene production

Liquid phase exfoliation(LPE)process for graphene production is usually carried out in stirred tank reactor and the interactions between the solvent and the graphite particles are important as to improve the production efficiency.In this paper,these interactions were revealed by computational fluid dynamics–discrete element method(CFD-DEM)method.Based on simulation results,both liquid phase flow hydrodynamics and particle motion behavior have been analyzed,which gave the general information of the multiphase flow behavior inside the stirred tank reactor as to graphene production.By calculating the threshold at the beginning of graphite exfoliation process,the shear force from the slip velocity was determined as the active force.These results can support the optimization of the graphene production process.

Computational Fluid Dynamics(CFD) Analysis and Optimization of Reconstructed Intake System of Cylinder Head Based on Slicing Reverse Method

To find out and improve the flow characteristics inside the intake system of cylinder head,the application of computational fluid dynamics(CFD)in the evaluation and optimization of the reconstructed intake system based on slicing reverse method was proposed.The flow characteristics were found out through CFD,and the velocity vector field,pressure field and turbulent kinetic energy field for different valve lifts were discussed,which were in good agreement with experimental data,and the quality of reconstruction was evaluated.In order to improve its flow characteristic,an optimization plan was proposed.The results show that the flow characteristics after optimization are obviously improved.The results can provide a reference for the design and optimization of the intake system of cylinder head.

COMPUTATIONAL FLUID DYNAMICS(CFD) SIMULATIONS OF DRAG REDUCTION WITH PERIODIC MICRO-STRUCTURED WALL

Computational fluid dynamics(CFD) simulations are adopted to investigate rectangular microchannel flows with various periodic micro-structured wall by introducing velocity slip boundary condition at low Reynolds number.The purpose of the current study is to numerically find out the effects of periodic micro-structured wall on the flow resistance in rectangular microchannel with the different spacings between microridges ranging from 15 to 60μm.The simulative results indicate that pressure drop with different spacing between microridges increases linearly with flow velocity and decreases monotonically with slip velocity;Pressure drop reduction also increases with the spacing between microridges at the same condition of slip velocity and flow velocity.The results of numerical simulation are compared with theoretical predictions and experimental results in the literatures.It is found that there is qualitative agreement between them.

A Computational Fluid Dynamics (CFD) Analysis of an Undulatory Mechanical Fin Driven by Shape Memory Alloy

许多鱼使用波动的鳍自己推进在在水下环境。这些运动机制有流行兴趣到许多研究人员。在现在的学习，我们执行被形状记忆合金(SMA ) 驾驶的波动的机械鳍的三维的不稳定的计算。计算的目的是调查与波动的机械鳍联系的力量生产的液体动力学。一个未组织的、基于格子的、不稳定的海军司烧解答者与自动适应重新协调被用来通过五个完全的周期在鳍附近计算不稳定的流动。鳍表面上的压力分发被计算并且综合上升提供被分解成的鳍力量并且推进。速度领域也在整个游泳周期被计算。最后，比较被进行根据波动的鳍(振幅，频率和波长) 的运动学的参数揭示力量产生的动力学。关键词计算液体动力学(CFD )- 波动的机械鳍 - 不稳定的流动 - 未组织的网孔 - 形状记忆合金(SMA ) 张永华收到了他的 B.Sc。在来自中国的科技的大学的精确乐器学和精确机械的度， Hefei，中国，在 2003。他现在在中国的科技的大学里正在追求他的博士学位。他出版了超过 10 份审阅杂志和会议报纸。他的当前的研究关于 biomimetic 用聪明的材料(SMA ) 的机器的鱼鳍。他的研究兴趣也包括在水下利用人工的肌肉的 microrobots。Jian-Hui 他收到了她的 B.Sc。在来自中国农业大学的计算机科学的度，中国北京，在 2003。她现在在精确机械和精确乐器学的部门正在追求她的 M.Sc 学位，中国的科技的大学。当前，她正在研究对微微滴透镜的制造的电场鈥檚 力量的影响。她出版了 5 篇审阅杂志和会议论文在最近二年。她的研究兴趣包括微光学、在水下的机器人。杨洁在科技的北京大学从物理化学的系毕业了，在 1969。他当前是在中国的科技的大学的精确机械和精确乐器学的系的一个教授。他领导集中于中国和 863 工程的国家自然科学基础支持的聪明的机器人的几个研究组。他的研究兴趣包括聪明的机器人，精确机械材料，和高速度摄影。张世武收到了他的 B.Sc。度在机械并且在来自中国的科技的大学的精确乐器学和精确机械的电力工程和博士学位， Hefei，中国。他当前是在精确机械和精确乐器学的系的一个研究助手，中国的科技的大学。他是在计算机科学系的一个研究助手，为 1.5 年的香港浸信会教友大学。他的当前的兴趣包括网智力，自治面向的计算，复杂系统，和聪明的机器人。家族 Huat 低从滑铁卢大学在 mechanical engineering 收到了他的 M.Sc 和博士学位，加拿大在 1983 和 1986，分别地。在在滑铁卢大学作为一个博士后的家伙度过二年以后，他加入了学院机械并且 Nanyang 工艺的大学的太空工程。他在 biomimetics，机器人学，康复，影响，电源传播系统，结构的动力学和颤动的区域是五本书和超过 90 篇杂志论文的作者。他的研究兴趣包括机器人学，颤动，影响，机器，机制，皮骨骼系统，和 mechatronics 设计。医生低是 IEEE， IASTED， SIAA 和 SiC-ToMM 的一个成员。他也是一个成员几技术，会议委员会，和杂志编委。他分别地在机器人学鱼和动力的皮骨骼上在研究工作上在二个 IEEE 会议赢得了奖品。

Review:Recent Development of High⁃Order⁃Spectral Method Combined with Computational Fluid Dynamics Method for Wave⁃Structure Interactions

The present paper reviews the recent developments of a high⁃order⁃spectral method(HOS)and the combination with computational fluid dynamics(CFD)method for wave⁃structure interactions.As the numerical simulations of wave⁃structure interaction require efficiency and accuracy,as well as the ability in calculating in open sea states,the HOS method has its strength in both generating extreme waves in open seas and fast convergence in simulations,while computational fluid dynamics(CFD)method has its advantages in simulating violent wave⁃structure interactions.This paper provides the new thoughts for fast and accurate simulations,as well as the future work on innovations in fine fluid field of numerical simulations.

Analysis of Temperature Rise in High-Speed Permanent Magnet Synchronous Traction Motors by Coupling the Equivalent Thermal Circuit Method and Computational Fluid Dynamics

To solve the problem of temperature rise caused by the high power density of high-speed permanent magnet synchronous traction motors,the temperature rise of various components in the motor is analyzed by coupling the equivalent thermal circuit method and computational fluid dynamics.Also,a cooling strategy is proposed to solve the problem of temperature rise,which is expected to prolong the service life of these devices.First,the theoretical bases of the approaches used to study heat transfer and fluid mechanics are discussed,then the fluid flow for the considered motor is analyzed,and the equivalent thermal circuit method is introduced for the calculation of the temperature rise.Finally,the stator,rotor loss,motor temperature rise,and the proposed cooling method are also explored through experiments.According to the results,the stator temperature at 50,000 r/min and 60,000 r/min at no-load operation is 68℃ and 76℃,respectively.By monitoring the temperature of the air outlets inside and outside the motor at different speeds,it is also found that the motor reaches a stable temperature rise after 65 min of operation.Coupling of the thermal circuit method and computational fluid dynamics is a strategy that can provide the average temperature rise of each component and can also comprehensively calculate the temperature of each local point.We conclude that a hybrid cooling strategy based on axial air cooling of the inner air duct of the motor and water cooling of the stator can meet the design requirements for the ventilation and cooling of this type of motors.

Computational Fluid Dynamics (CFD) Modelling to Estimate Fluvial Bank Erosion—A Case Study

River bank erosion models are an important prerequisite for understanding the development of river meanders and for estimating likely land-loss and potential danger to floodplain infrastructure. Although bank erosion models have been developed that consider large-scale mass failure, the contribution of fluvial erosion (the process of particle-by-particle erosion due to the shearing action of the river flow) to bank retreat has not received as much consideration. In principle, such fluvial bank erosion rates can be quantified using excess shear stress formulations, but in practice, it has proven difficult to estimate the parameters involved. In this study, a series of three-dimensional Computational Fluid Dynamics (CFD) simulations for a meander loop on the River Asker (200 m long) at Bridport in southern England were undertaken to elucidate the overall flow structures and in particular to provide estimates of the applied fluid shear stress exerted on the riverbanks. The CFD models, which simulated relatively low and relatively high flow conditions, were established using Fluent 6.2 software. The modelling outcomes show that the key qualitative features of the flow endure even as flow discharge varies. At bank full, the degrees of velocity and simulated shear stresses within the inner bank separation zones are shown to be higher than those observed under low flow conditions, and that these elevated shear stresses may be sufficient to result in the removal of accumulated sediments into the main downstream flow.

Numerical simulation of a direct internal reforming solid oxide fuel cell using computational fluid dynamics method

A detailed mathematical model of a direct internal reforming solid oxide fuel cell(DIR-SOFC) incorporating with simulation of chemical and physical processes in the fuel cell is presented. The model is developed based on the reforming and electrochemical reaction mechanisms,mass and energy conservation,and heat transfer. A computational fluid dynamics(CFD) method is used for solving the complicated multiple partial differential equations(PDEs) to obtain the numerical approximations. The resulting distributions of chemical species concentrations,temperature and current density in a cross-flow DIR-SOFC are given and analyzed in detail. Further,the influence between distributions of chemical species concentrations,temperature and current density during the simulation is illustrated and discussed. The heat and mass transfer,and the kinetics of reforming and electrochemical reactions have significant effects on the parameter distributions within the cell. The results show the particular characteristics of the DIR-SOFC among fuel cells,and can aid in stack design and control.

Application of Computational Fluid Dynamics and Fluid Structure Interaction Techniques for Calculating the 3D Transient Flow of Journal Bearings Coupled with Rotor Systems

Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simplified physical model and classic Reynolds equation are always applied. While the application of the general computational fluid dynamics (CFD)-fluid structure interaction (FSI) techniques is more beneficial for analysis of the fluid field in a journal bearing when more detailed solutions are needed. This paper deals with the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearings and rotor dynamics with CFD-FSI techniques. The fluid dynamics of oil film is calculated by applying the so-called ''dynamic mesh'' technique. A new mesh movement approach is presented while the dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. The proposed mesh movement approach is based on the structured mesh. When the journal moves, the movement distance of every grid in the flow field of bearing can be calculated, and then the update of the volume mesh can be handled automatically by user defined function (UDF). The journal displacement at each time step is obtained by solving the moving equations of the rotor-bearing system under the known oil film force condition. A case study is carried out to calculate the locus of the journal center and pressure distribution of the journal in order to prove the feasibility of this method. The calculating results indicate that the proposed method can predict the transient flow field of a journal bearing in a rotor-bearing system where more realistic models are involved. The presented calculation method provides a basis for studying the nonlinear dynamic behavior of a general rotor-bearing system.

COMPUTATIONAL FLUID DYNAMICS RESEARCH ON PRESSURE LOSS OF CROSS-FLOW PERFORATED MUFFLER

The pressure loss of cross-flow perforated muffler has been computed with the procedure of physical modeling,simulation and data processing. Three-dimensional computational fluid dynam-ics (CFD) has been used to investigate the relations of porosities,flow velocity and diameter of the holes with the pressure loss. Accordingly,some preliminary results have been obtained that pressure loss increases with porosity descent as nearly a hyperbolic trend,rising flow velocity of the input makes the pressure loss increasing with parabola trend,diameter of holes affects little about pressure loss of the muffler. Otherwise,the holes on the perforated pipes make the air flow gently and meanly,which decreases the air impact to the wall and pipes in the muffler. A practical perforated muffler is used to illustrate the available of this method for pressure loss computation,and the comparison shows that the computation results with the method of CFD has reference value for muffler design.

Computational fluid dynamics simulation of a novel bioreactor forsophorolipid production

This paper describes three-dimensional computational fluid dynamics(CFD) simulations of gas–liquid flow in a novel laboratory-scale bioreactor contained dual ventilation-pipe and double sieve-plate bioreactor(DVDSB)used for sophorolipid(SL) production. To evaluate the role of hydrodynamics in reactor design, the comparisons between conventional fed-batch fermenter and DVDSB on the hydrodynamic behavior are predicted by the CFD methods. Important hydrodynamic parameters of the gas–liquid two-phase system such as the liquid phase velocity field, turbulent kinetic energy and volume-averaged overall and time-averaged local gas holdups were simulated and analyzed in detail. The numerical results were also validated by experimental measurements of overall gas holdups. The yield of sophorolipids was significantly improved to 484 g·L^(-1)with a 320 h fermentation period in the new reactor.

The influence of temperature on flow-induced forces on quartz-crystal-microbalance sensors in a Chinese liquor identification electronic-nose: three-dimensional computational fluid dynamics simulation and analysis

An electronic-nose is developed based on eight quartz-crystal-microbalance (QCM) gas sensors in a sensor box, and is used to detect Chinese liquors at room temperature. Each sensor is a highly-accurate and highly-sensitive oscillator that has experienced airflow disturbances under the condition of varying room temperatures due to unstable flow-induced forces on the sensors surfaces. The three-dimensional (3D) nature of the airflow inside the sensor box and the interactions of the airflow on the sensors surfaces at different temperatures are studied by computational fluid dynamics (CFD) tools. Higher simulation accuracy is achieved by optimizing meshes, meshing the computational domain using a fine unstructural tetrahedron mesh. An optimum temperature, 30 ℃, is obtained by analyzing the distributions of velocity streamlines and the static pressure, as well as the flow-induced forces over time, all of which may be used to improve the identification accuracy of the electronic-nose for achieving stable and repeatable signals by removing the influence of temperature.

Computational simulation of fluid dynamics in a tubular stirred reactor

The flow and concentration fields in a new style tubular stirred reactor were simulated by simulating the fluids dynamics(CFD),in which FLUENT software was used and the standard k-ε model and multiple reference frame(MRF) were adopted. The various values of initial rotating speed and inlet flow rate were adopted. Simulations were validated with experimental residence time distribution(RTD) determination. It is shown that the fluid flow is very turbulent and the flow pattern approaches to the plug flow. The velocity increases from shaft to the end of impeller,and the gradient is enlarged by increasing the rotating speed. Comparison between RTD curves shows that agitation can improve the performance of reactor. As the flow rate increases,the mean residence time decreases proportionally,and the variance of RTD lessens as well. When rotating speed increases to a certain value,the variance of RTD is enlarged by increasing rotating speed,but the mean residence time has no obvious change.

Computational Fluid Dynamics Analysis of Shroud Design on Hemodynamic Performance and Blood Damage in a Centrifugal Blood Pump

Patients with extracorporeal membrane oxygenation still suffer from high rates of complication that linked to the flow field within the blood pump.So it is essential to optimise the geometry of the pump.The specification of shroud design is arguably the necessary design parameter in the centrifugal pump.However,the hemodynamic performances of the different shroud designs have not been studied extensively.In this study,ten different shroud designs were made and divided into two groups as the different covering locations(A:Covering the blade leading edge,B:Covering the blade trailing edge).In every group,six shroud designs with the covering proportions of 0,1/5,2/5,3/5,4/5,1 were made.Detailed computational fluid dynamics(CFD)analyses were performed to investigate their effects on hemodynamics and hydraulic performance at the constant flow condition(4000 rpm,5 L/min).The percentage volumes of the scalar shear stress in specific threshold(τ<1 Pa:Thrombosis,τ>9 Pa:the destruction of von Willebrand factor,τ>50 Pa:Platelet activation,τ>150 Pa:Break of red blood)were used to compare the blood damage of the different shroud designs.Also,the modified index of hemolysis(MIH)were calculated based on a Eulerian approach for different pumps.CFD simulations predicted an increase in the pump head,hydraulic efficiency,a fraction of fluid volume with scalar shear stress values above a threshold(9 Pa,50 Pa,150 Pa)and MIH with increasing shroud covering proportions from 0 to 1 in the same covering location.Also,these above results were higher in group B than group A.This means that the risks of the hemolysis,thrombosis and bleeding increased as the rise of the covering proportion and they were higher in the pump whose shroud covers the blade trailing edge.

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.

Computational Fluid Dynamics Based Bulbous Bow Optimization Using a Genetic Algorithm

计算液体动力学(CFD ) 在预言一艘轮船的流动行为起一个主要作用。与快计算机和柔韧的 CFD 软件的开发， CFD 在轮船工业为设计者和工程师成为了一个重要工具。在这份报纸，一艘轮船的壳形式作为一个优化工具作为一个计算工具和一个基因算法用 CFD 为全部的抵抗被优化。CFD 基于优化由基于设计参数包含几何学的自动产生的主要的步组成，网孔的自动产生，液体的自动分析计算要求的目的 / 费用的流动功能，并且最后为优化评估费用的一个优化工具。在这篇论文，一个基因算法程序的集成，在 MATLAB 写，与几何学和协调软件带风险的策略和 CFD 分析软件被执行流畅。添加剂的不同几何学球状的鞠躬基于设计参数在原来的壳被合并。这些设计变量被优化完成全部的抵抗的最小的费用功能。有 CFD 工具的一个基因算法的集成证明为壳形式优化有效。

Computational fluid dynamics simulation of gas-liquid two phases flow in 320 m^3 air-blowing mechanical flotation cell using different turbulence models

According to the recently developed single-trough floating machine with the world's largest volume(inflatable mechanical agitation flotation machine with volume of 320 m3) in China, the gas-fluid two-phase flow in flotation cell was simulated using computational fluid dynamics method. It is shown that hexahedral mesh scheme is more suitable for the complex structure of the flotation cell than tetrahedral mesh scheme, and a mesh quality ranging from 0.7 to 1.0 is obtained. Comparative studies of the standard k-ε, k-ω and realizable k-ε turbulence models were carried out. It is indicated that the standard k-ε turbulence model could give a result relatively close to the practice and the liquid phase flow field is well characterized. In addition, two obvious recirculation zones are formed in the mixing zones, and the pressure on the rotor and stator is well characterized. Furthermore, the simulation results using improved standard k-ε turbulence model show that surface tension coefficient of 0.072, drag model of Grace and coefficient of 4, and lift coefficient of 0.001 can be achieved. The research results suggest that gas-fluid two-phase flow in large flotation cell can be well simulated using computational fluid dynamics method.

Optimization study of a PEM fuel cell performance using 3D multi-phase computational fluid dynamics model

An optimization study using a comprehensive 3D, multi-phase, non-isothermal model of a PEM (proton exchange membrane) fuel cell that incorporates significant physical processes and key parameters affecting fuel cell performance is pre-sented and discussed in detail. The model accounts for both gas and liquid phase in the same computational domain, and thus allows for the implementation of phase change inside the gas diffusion layers. The model includes the transport of gaseous species, liquid water, protons, energy, and water dissolved in the ion-conducting polymer. Water is assumed to be exchanged among three phases: liquid, vapour, and dissolved, with equilibrium among these phases being assumed. This model also takes into account convection and diffusion of different species in the channels as well as in the porous gas diffusion layer, heat transfer in the solids as well as in the gases, and electrochemical reactions. The results showed that the present multi-phase model is capable of iden-tifying important parameters for the wetting behaviour of the gas diffusion layers and can be used to identify conditions that might lead to the onset of pore plugging, which has a detrimental effect on the fuel cell performance. This model is used to study the effects of several operating, design, and material parameters on fuel cell performance. Detailed analyses of the fuel cell per-formance under various operating conditions have been conducted and examined.

Computational Fluid Dynamics Simulation of Liquid-Phase FCC Diesel Hydrotreating in Tubular Reactor

The computational fluid dynamics(CFD) code, FLUENT, was used to simulate the liquid-phase FCC diesel hydrotreating tubular reactor with a ceramic membrane tube dispenser. The chemical reaction and reaction heat were added to the model by user-defined function(UDF), showing the distribution of temperature and content of sulfides, nitrides, bicyclic aromatics and monocyclic aromatics in different parts of the reaction bed. When the pressure was 6.5 MPa, the amount of mixing hydrogen was 0.84%(m), the space velocity was 2 h-1 and the inlet temperature was 633 K, the temperature reached a maximum at a height of 0.15 m, and the range of radial temperature reached its maximum(2.5 K) at a height of 0.15 m. It indicated that the proper ratio of height to diameter of catalyst bed in the tubular reactor was 5-6. The increase of inlet temperature, the mixing hydrogen and the decrease of space velocity led to the decrease in the content of bicyclic aromatics, sulfides and nitrides, and the increase in monocyclic aromatics content, while the high temperature increased. The results were in good agreement with experimental data, indicating to the high accuracy of the model.

Computational fluid dynamics simulations of respiratory airflow in human nasal cavity and its characteristic dimension study

为了在呼吸和特征期间在人的鼻音洞学习气流分发，鼻音的参数组织， 30 个成年鼻音洞模型的三维的、解剖地精确的代表基于从正常的人收集的处理断层摄影术图象被重建。在鼻音洞的气流领域被液体动力学与有限元素软件 ANSYS 模仿。结果证明人的鼻音洞结构的差别在鼻音洞和通过普通鼻音道的主要飞机飞行时所生之气流的变化导致了不同气流分发。在鼻音阀门和鼻音门厅的区域的鼻音抵抗说明了多于全面抵抗的一半。鼻音洞的典型模型根据从原来的模型推出的典型的点和尺寸被提取。它证明几何结构或二种模型的气流领域是类似的。典型尺寸是能适当地在鼻音洞上在模型研究代表原来的模型的鼻音洞的典型参数。