Computational fluid dynamics modeling of rapid pyrolysis of solid waste magnesium nitrate hydrate under different injection methods

This study developed a numerical model to efficiently treat solid waste magnesium nitrate hydrate through multi-step chemical reactions.The model simulates two-phase flow,heat,and mass transfer processes in a pyrolysis furnace to improve the decomposition rate of magnesium nitrate.The performance of multi-nozzle and single-nozzle injection methods was evaluated,and the effects of primary and secondary nozzle flow ratios,velocity ratios,and secondary nozzle inclination angles on the decomposition rate were investigated.Results indicate that multi-nozzle injection has a higher conversion efficiency and decomposition rate than single-nozzle injection,with a 10.3%higher conversion rate under the design parameters.The decomposition rate is primarily dependent on the average residence time of particles,which can be increased by decreasing flow rate and velocity ratios and increasing the inclination angle of secondary nozzles.The optimal parameters are injection flow ratio of 40%,injection velocity ratio of 0.6,and secondary nozzle inclination of 30°,corresponding to a maximum decomposition rate of 99.33%.

Application of computational fluid dynamics in design of viscous dampers-CFD modeling and full-scale dynamic testing

Computational fluid dynamics(CFD)provides a powerful tool for investigating complicated fluid flows.This paper aims to study the applicability of CFD in the preliminary design of linear and nonlinear fluid viscous dampers.Two fluid viscous dampers were designed based on CFD models.The first device was a linear viscous damper with straight orifices.The second was a nonlinear viscous damper containing a one-way pressure-responsive valve inside its orifices.Both dampers were detailed based on CFD simulations,and their internal fluid flows were investigated.Full-scale specimens of both dampers were manufactured and tested under dynamic loads.According to the tests results,both dampers demonstrate stable cyclic behaviors,and as expected,the nonlinear damper generally tends to dissipate more energy compared to its linear counterpart.Good compatibility was achieved between the experimentally measured damper force-velocity curves and those estimated from CFD analyses.Using a thermography camera,a rise in temperature of the dampers was measured during the tests.It was found that output force of the manufactured devices was virtually independent of temperature even during long duration loadings.Accordingly,temperature dependence can be ignored in CFD models,because a reliable temperature compensator mechanism was used(or intended to be used)by the damper manufacturer.

A simplified approach to modelling blasts in computational fluid dynamics (CFD)

This paper presents a time-efficient numerical approach to modelling high explosive(HE)blastwave propagation using Computational Fluid Dynamics(CFD).One of the main issues of using conventional CFD modelling in high explosive simulations is the ability to accurately define the initial blastwave properties that arise from the ignition and consequent explosion.Specialised codes often employ Jones-Wilkins-Lee(JWL)or similar equation of state(EOS)to simulate blasts.However,most available CFD codes are limited in terms of EOS modelling.They are restrictive to the Ideal Gas Law(IGL)for compressible flows,which is generally unsuitable for blast simulations.To this end,this paper presents a numerical approach to simulate blastwave propagation for any generic CFD code using the IGL EOS.A new method known as the Input Cavity Method(ICM)is defined where input conditions of the high explosives are given in the form of pressure,velocity and temperature time-history curves.These time history curves are input at a certain distance from the centre of the charge.It is shown that the ICM numerical method can accurately predict over-pressure and impulse time history at measured locations for the incident,reflective and complex multiple reflection scenarios with high numerical accuracy compared to experimental measurements.The ICM is compared to the Pressure Bubble Method(PBM),a common approach to replicating initial conditions for a high explosive in Finite Volume modelling.It is shown that the ICM outperforms the PBM on multiple fronts,such as peak values and overall overpressure curve shape.Finally,the paper also presents the importance of choosing an appropriate solver between the Pressure Based Solver(PBS)and Density-Based Solver(DBS)and provides the advantages and disadvantages of either choice.In general,it is shown that the PBS can resolve and capture the interactions of blastwaves to a higher degree of resolution than the DBS.This is achieved at a much higher computational cost,showing that the DBS is much preferred for quick turnarounds.

Flow Field Characteristics of Multi-Trophic Artificial Reef Based on Computation Fluid Dynamics

On the basis of computational fluid dynamics,the flow field characteristics of multi-trophic artificial reefs,including the flow field distribution features of a single reef under three different velocities and the effect of spacing between reefs on flow scale and the flow state,were analyzed.Results indicate upwelling,slow flow,and eddy around a single reef.Maximum velocity,height,and volume of upwelling in front of a single reef were positively correlated with inflow velocity.The length and volume of slow flow increased with the increase in inflow velocity.Eddies were present both inside and backward,and vorticity was positively correlated with inflow velocity.Space between reefs had a minor influence on the maximum velocity and height of upwelling.With the increase in space from 0.5 L to 1.5 L(L is the reef lehgth),the length of slow flow in the front and back of the combined reefs increased slightly.When the space was 2.0 L,the length of the slow flow decreased.In four different spaces,eddies were present inside and at the back of each reef.The maximum vorticity was negatively correlated with space from 0.5 L to 1.5 L,but under 2.0 L space,the maximum vorticity was close to the vorticity of a single reef under the same inflow velocity.

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.

Preliminary Evaluation of Hemodynamic Effects of Fontan Palliation on Renal Artery Using Computational Fluid Dynamics

Background:The assessment of renal function is important to the prognosis of patients needing Fontan palliation due to the reconstructed compromised circulation.To know the relationship between the kidney perfusion and hemodynamic characteristics during surgical design could reduce the risk of acute kidney injury(AKI)and the postoperative complications.However,the issue is still unsolved because the current clinical evaluation methods are unable to predict the hemodynamic changes in renal artery(RA).Methods:We reconstructed a three-dimensional(3D)vascular model of a patient requiring Fontan palliation.The technique of computational fluid dynamics(CFD)was utilized to explore the changes of RA hemodynamics under different possible blood flow rates.The relationship between the kidney perfusion and hemodynamic characteristics was investigated.Results:The calculated results indicated the declined tendency of the pressure and pressure drop as the flow rate decreased.When the flow rate decreased to two-thirds of its baseline,both the pressure of left renal artery(LRA)and the pressure of right renal artery(RRA)dipped below 50%,and the pressure of RRA fell more quickly than that of LRA.Uneven distribution of WSS was observed on the trunk of RA,and the lowest WSS was found at the distal of RA.The average WSS in RA dropped to around 50%as the flow rate reached one-third of its baseline.Conclusions:As a promising approach,CFD can be utilized to quantitatively evaluate the hemodynamic characteristics of RA and contribute to offsetting the drawbacks of clinical assessments of renal function,to help realize better prognosis for the patients with Fontan palliation.

Computational fluid dynamics(CFD) simulation of effect of baffles on separation in mixer settler

The main ideas in the development of the solvent extraction mixer settler focused on achieving clean phase separation,minimizing the loss of the reagents and decreasing the surface area of the settlers.The role of baffles in a mechanically agitated vessel is to ensure even distribution,reduce settler turbulence,promote the stability of power drawn by the impeller and to prevent swirling and vortexing of liquid,thus,greatly improving the mixing of liquid.The insertion of the appropriate number of baffles clearly improves the extent of liquid mixing.However,excessive baffling would interrupt liquid mixing and lengthen the mixing time.Computational fluid dynamics(CFD) provides a tool for determining detailed information on fluid flow(hydrodynamics) which is necessary for modeling subprocesses in mixer settler.A total of 54 final CFD runs were carried out representing different combinations of variables like number of baffles,density and impeller speed.CFD data shows that amount of separation increases with increasing baffles number and decreasing impeller speed.

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。

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) 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.

Application of computational fluid dynamic to model the hydraulic performance of subsurface flow wetlands

A subsurface flow wetland(SSFW)was simulated using a commercial computational fluid dynamic(CFD)code.The constructed media was simulated using porous media and the liquid resident time distribution(RTD)in the SSFW was obtained using the particle trajectory model.The effect of wetland configuration and operating conditions on the hydraulic performance of the SSFW were investigated.The results indicated that the hydraulic performance of the SSFW was predominantly affected by the wetland configuration.The hydraulic effciency of the SSFW with an inlet at the middle edge of the upper media was 0.584 and the best among the SSFWs with an inlet at the top,the middle,and the bottom edge of the upper media.The constructed media affected the hydraulic performance by the ratio(K)of the upper and lower media resistance.The selection of appropriate media resistance in the protection layer can improve the hydraulic effciency.When the viscous resistance coeffcient of the media in the protection layer changed from 2.315×105 to 1.200×108,the hydraulic effciency of the SSFW increased from 0.301 to 0.751.However,the effect of operating conditions on the hydraulic effciency of the SSFW was slight.

Computational fluid dynamics evaluation of the effect of different city designs on the wind environment of a downwind natural heritage site

Disturbance in wind regime and sand erosion deposition balance may lead to burial and eventual vanishing of a site.This study conducted 3D computational fluid dynamics(CFD)simulations to evaluate the effect of a proposed city design on the wind environment of the Crescent Spring,a downwind natural heritage site located in Dunhuang,Northwestern China.Satellite terrain data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer(ASTER)Digital Elevation Model(DEM)were used to construct the solid surface model.Steady-state Reynolds Averaged Navier-Stokes equations(RANS)with shear stress transport(SST)k-ωturbulence model were then applied to solve the flow field problems.Land-use changes were modeled implicitly by dividing the underlying surface into different areas and by applying corresponding aerodynamic roughness lengths.Simulations were performed by using cases with different city areas and building heights.Results show that the selected model could capture the surface roughness changes and could adjust wind profile over a large area.Wind profiles varied over the greenfield to the north and over the Gobi land to the east of the spring.Therefore,different wind speed reduction effects were observed from various city construction scenarios.The current city design would lead to about 2 m/s of wind speed reduction at the downwind city edge and about 1 m/s of wind speed reduction at the north of the spring at 35-m height.Reducing the city height in the north greenfield area could efficiently eliminate the negative effects of wind spee.By contrast,restricting the city area worked better in the eastern Gobi area compared with other parts of the study area.Wind speed reduction in areas near the spring could be limited to 0.1 m/s by combining these two abatement strategies.The CFD method could be applied to simulate the wind environment affected by other land-use changes over a large terrain.

Structural parameter optimization for novel internal-loop iron–carbon micro-electrolysis reactors using computational fluid dynamics

It is generally recognized that internal-loop reactors are well-developed mass and heat-transfer multiphase flow reactors. However, the internal flow field in the internal-loop reactor is influenced by the structure parameter of the reactor, which has a great effect on the reaction efficiency. In this study, the computational fluid dynamics simulation method was used to determine the influence of reactor structure on flow field, and a volume-offluid model was employed to simulate the gas–liquid, two-phase flow of the internal-loop micro-electrolysis reactor. Hydrodynamic factors were optimized when the height-to-diameter ratio was 4:1, diameter ratio was9:1, draft-tube axial height was 90 mm. Three-dimensional simulations for the water distributor were carried out, and the results suggested that the optimal conditions are as follows: the number of water distribution pipes was four, and an inhomogeneous water distribution was used. According to the results of the simulation,the suitable structure can be used to achieve good fluid mechanical properties, such as the good liquid circulation velocity and gas holdup, which provides a good theoretical foundation for the application of the reactor.

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.

Flow Ripple of Axial Piston Pump with Computational Fluid Dynamic Simulation Using Compressible Hydraulic Oil

The flow ripple, which is the source of noise in an axial piston pump, is widely studied today with the computational fluid dynamic(CFD) technology development. In the traditional CFD modeling, the fluid compressibility, which strongly influences the accuracy of the flow ripple simulation results, is often neglected. So a compressible sub-model was added with user defined function(UDF) in the CFD model to predict the flow ripple. At the same time, a test rig of flow ripple was built to study the validity of simulation. The flow ripple of pump was tested with different working parameters, including the rotation speed and the working pressure. The comparisons with experimental results show that the validity of the CFD model with compressible hydraulic oil is acceptable in analyzing the flow ripple characteristics. In this paper, the improved CFD model increases the accuracy of flow ripple rate to about one-magnitude order. Therefore, the compressible model of hydraulic oil is necessary in the flow ripple investigation of CFD simulation. The compressibility of hydraulic oil has significant effect on flow ripple, and the compression ripple takes about 88% of the total flow ripple of pump. Leakage ripple has the lowest proportion of about 4%, and geometrical ripple leakage ripple takes the remnant 8%. Besides, the influence of working parameters was investigated through the CFD simulations and experimental measurements. Comparison results show that the amplitude of flow ripple grows with the increasing of rotation speed and working pressure, and the flow ripple rate is independent of the rotation speed. However, flow ripple rate of piston pump grows with the increasing of working pressure, because the leakage ripple will increase with the pressure growing. The investigation on flow ripple of an axial piston pump using compressible hydraulic oil provides a more validity simulation model for the CFD analyzing and is beneficial to further understanding of the flow ripple characteristics in an axial piston pump.

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.