Modélisation Mathématique de la Décantation de la Boue Rouge

A good performance of the solid‐liquid unit operation is required for the economical exploitation of the Bayer process. A computational fluid dynamics (CFD) model simulating the operation of the last washing stage mud thickener of a large Canadian alumina plant is presented. The parametric study of the impact of changes in four parameters shows that the diameter of flocculated red mud particles, the feed flow rate and the radius of the feed well are critical parameters for the operation of the thickener.     

Computational fluid dynamics (CFD) modeling of spouted bed: Influence of frictional stress, maximum packing limit and coefficient of restitution of particles

Following the previous article [Du, W., Bao, X., Xu, J., Wei, W., 2006. Computational fluid dynamics (CFD) modeling of spouted bed: assessment of drag coefficient correlations. Chemical Engineering Science 61 (5), 1401-1420], this contribution describes the influences of the frictional stress, maximum packing limit and coefficient of restitution of particles on CFD simulation of spouted beds. Using the two-fluid method embedded in the commercial CFD simulation package Fluent 6.1, the spouting hydrodynamics of a cylindrical-conical spouted bed was simulated and verified with the experimental data of He et al. [He, Y.L., Lim, C.J., Grace, J.R., Zhu, J.X., Qin, S.Z., 1994a. Measurements of voidage profiles in spouted beds. Canadian Journal of Chemical Engineering 72 (4), 229-234; He, Y.L., Qin, S.Z., Lim, C.J., Grace, J.R., 1994b. Particle velocity profiles and solid flow patterns in spouted beds. Canadian Journal of Chemical Engineering 72(8), 561-568]. The results showed that, for coarse particles, the frictional stress is important only for the annulus computation and has no obvious effects on the hydrodynamics of the solids flow in the spout region. The specification of the maximum packing limit could significantly affect the properties of the pseudo-fluid phase of the particles by changing the radial distribution function. The strong dependence of the pseudo-fluid properties of the particle phase, such as pressure, bulk viscosity and shear viscosity, on the granular temperature accounts for the influence of the coefficient of restitution of particles on CFD modeling. The solids volume fraction at loose packing state is suitable for spouted bed simulations, and a pretest of the coefficient of restitution of particles must be conducted when no experimental datum is available.     

Liquid flow and phase holdup—measurement and CFD modeling for two-and three-phase bubble columns

Bubble columns are an important class of contacting devices in chemical industry and biotechnology. Their simple setup makes them ideal reactors for two- and three-phase operations such as fermentations or heterogeneous catalysis. Still, design and operation of these reactors is subject to widely empirical scale-up strategies. With recent advances in the development of measurement techniques, a more detailed approach to the development of optimized reactors for specific operations should become possible. This report is based on detailed measurements of local dispersed phase holdups in a pilot plant-sized bubble column operated at high superficial gas velocities and solid holdups. It deals with the influence of superficial gas velocity, solid loading and sparger geometry on measured and computed liquid flow velocities and holdup distributions. Liquid velocity measurements have been performed using the electrodiffusion method, modeling calculations have been carried out using the computational fluid dynamics (CFD) code CFX-4.3. Measurement results presented here give an insight into the development of liquid circulation and fluctuating velocity distribution depending on superficial gas velocity, solid loading and sparger geometry. CFD results implementing a multi-fluid model with k-ε turbulence and special momentum exchange terms for direct gas-solid interactions show that, even on standard PC workstations, this kind of computations can deliver qualitatively reasonable agreement with measurements.     

计量用低速风洞结构参数仿真研究

为准确分析风洞结构参数对所产生的风场稳定性的影响规律,以现有低速风洞为蓝本,通过改变其试验段结构参数建立多个不同参数试验模型;采用ansys CFD对建立的多个新模型进行结构流体仿真,对仿真结果进行数据拟合,找出风洞收缩段曲线结构参数变化对试验段轴向风速梯度和法向风速均匀性的影响;仿真实验结果表明,试验段法向中心面的有效试验区的均匀性系数随着收缩段长度增加而减小,到一定程度趋于稳定,风洞模型在L＞ 23 cm后风场均匀性系数基本处于稳定,试验段前半段的风速轴向梯度明显大于后半段的风速轴向梯度,有效试验区域多集中在后半段,风洞模型中轴向有效试验区域x＞(10～15) cm,可以为风洞的设计提供可靠参考.     

峡谷和垭口地形风场特征的CFD数值模拟

为获得峡谷和垭口地形的风场特征和典型位置的风加速效应,采用计算流体动力学(CFD)方法进行模拟计算,将计算得到的单山结果与风洞试验及规范进行对比以验证CFD计算的有效性,对峡谷和垭口地形进行数值模拟计算,分析峡谷和垭口在不同山脚间距时的加速效应,针对内侧山脚和山顶处的加速比给出设计建议.研究表明:山顶处加速比最大;山体横风切面的加速效应比顺风切面显著;CFD模拟与风洞试验结果吻合较好;山顶处,垭口地形风加速效应比峡谷和单山都大;内侧山脚加速比随着两山靠近而增大;内侧山脚处,峡谷地形的加速比小于规范下限,垭口地形在山间距小于一半山体底部直径、离山表面高度低于0.4倍山体高度时的加速比大于规范上限;山顶处的加速比在各种工况下均比较接近;不建议将山顶和垭口位置作为构筑物的选址地点.     

斜板沉淀池前配水渠的数值模拟及结构优化

针对配水渠出水优化措施单一、优化效果欠佳的问题,运用CFD软件,采用Realizable k-ε湍流模型对其流速场进行数值模拟,探究了进口宽度（b）和配水渠宽度（B）变化时出水均匀度最优的配水渠长度（L）,并优化了挡墙在双段配水渠中的最佳位置。结果表明：配水渠进口集中主流在池内流域空间的扩散程度是出水均匀度的主要影响因素;当b在1 200~1 600 mm范围时,L取1 750~2 250 mm时的出水均匀度最优,若b大于1 600 mm,最优的L值须适当增加,但不应大于3 000 mm;当B为3 900 mm时,L最佳取值为1 750~2 250 mm,当B为5 300或6 700 mm时,最佳的L值应增加500 mm左右;采用双段配水渠时,挡墙位置应设在进口侧,而不应在配水渠的中间位置。该研究可为配水渠的设计提供一定的理论指导。     

CFD在调压室设计计算中的可行性研究

采用C FD方法对简单调压室和阻抗式调压室进行数值模拟,计算出不同分流比下,调压室的阻力系数值,将模拟结果同文献中的试验值进行对比分析。结果表明,模拟曲线和试验曲线的趋势基本一致,并且模拟数值和试验数值高度吻合,该方法可应用在调压室的阻力系数研究中。在此基础之上,该方法应用在实际电站调压室的模拟中,并通过水力过渡过程的计算,验证了该结果的准确性。最后得出结论, C FD方法可应用于调压室的设计计算。     

Optimal Design of Two-Chamber Gas Distributor with CFD Approach

Computational fluid dynamics( CFD) is used to investigate a new type of two-chamber natural gas distributor,which has a natural gas inlet and nine nozzle outlets. The uniformity at the outlet of distributor is practice proven to have significant degree influence on its comprehensive performance. To improve the uniformity at the nozzles of the gas distributor,CFD modeling with the RNG k-ε turbulence model is undertaken to understand the mass flow rate of nozzles with reference to different length of chambers and the most optimal length is obtained. The internal flow pattern of the natural gas distributor is analyzed. It is found that the local maximum deviation of the nozzle outflow rate increases with the increase of chambers length when the length is more than 64 mm. The results provide useful suggestions for the optimal design of two-chamber natural gas distributor.     

基于Eulerian模型的三维立式脱水沉降罐数值模拟

利用计算流体力学(CFD)分析软件ANSYS(FLUENT)的多相流Eulerian模型对三维立式脱水沉降罐油水分离过程进行了非稳态数值模拟,同时使用用户自定义函数(UDF)编写流体物性值随温度的变化关系。从模拟结果中观察了温度场、体积分数和流场的细节特征,结果发现,配液管温度、油相体积分数影响配液孔流速;进液温度在60~80℃时,较高的温度总是有利于油水分离;罐内油相速度在乳化层处扩散。     

潜水搅拌器安装角度对搅拌效果的影响

研究潜水搅拌器水平安装角度对搅拌池内流场的影响,建立不同的水平安装角度,通过Fluent对潜水搅拌机的搅拌槽内流场进行三维数值模拟,得出不同方案的速度分布情况.利用UDF模块,分别计算流场中流速达到搅拌效果的有效搅拌流体体积及其占整个流场体积的百分比,通过比较,选出最优的潜水搅拌器安装方案,提出了评价潜水搅拌器效能及其安装布置优劣的新方法——有效搅拌域法,利用此方法,使潜水搅拌器的搅拌效果分析更加准确.