行星式搅拌釜内固液混合时间的数值计算

行星式搅拌装置内搅拌桨的运动轨迹复杂,对固体颗粒与高黏度聚合物熔体的混合效果较好。混合时间是表征搅拌釜内流体混合状况、评定搅拌釜效率的重要参数之一。利用FLUENT软件数值模拟一种行星式搅拌釜内高黏固液两相混合过程,采用传统混合时间定义方法和体积分数法2种方法计算搅拌桨不同自转转速的混合时间,并将2种方法的计算结果进行比较;采用体积分数法计算搅拌桨不同安装高度时的混合时间。计算中采用欧拉模型,使用动网格技术,利用FLUENT的用户自定义函数确定搅拌桨的速度。数值计算结果表明,采用选取监测点计算混合时间的方法,不同监测点的混合时间有较大差异,为保证全釜内混合均匀,应选取混合时间最长的监测点;选取监测点和体积分数2种混合时间计算方法得到的混合时间基本相同;随着搅拌桨自转转速的提高,混合时间明显缩短;采用釜底加料方式,搅拌桨安装高度从20mm提高到60mm时混合时间缩短。     

微机在多釜串联反应器设计计算中的应用

本文用数值方法代替 Jones 图解法进行多釜串联反应器的设计计算。其优点是简便、精确。其适用范围基本上与图解法相同,但可适用于某些变容体系。本文提供的程序还可同时计算活塞流反应器、间歇搅拌釜式反应器以及连续搅拌釜式反应器的有效容积,适于化学反应工程教学用。     

基于多尺度的声测量搅拌釜内物料特征

通过声波信号在线分析反应器内物料特征具有快速、无损、安全、不侵入流场的优点。讨论了利用声发射信号在线分析搅拌釜内物料浓度与粒度的方法。先通过小波变换多尺度分解原始声信号,然后以分解后各细节信号小波系数幅值绝对值加和为特征变量,釜内物料浓度或颗粒平均粒度和声发射信号的关系再用判别分析方法加以区分,考察了信号长度、分解尺度以及不同小波对判别准确性的影响,结果表明,当物料的浓度一定时,基于多尺度分析的声测量方法可以准确地对釜内物料的粒度进行分类。     

连续搅拌釜式反应器的自耦比例–积分–微分控制

针对一类参数不确定的连续搅拌釜式反应器,使用了一种与被控对象无关的自耦比例–积分–微分(autocoupling proportional-integral-differential, ACPID)控制方法.该方法将系统内部所有不确定因素及外部扰动定义为一个总扰动,建立了以总扰动为激励的受控误差系统,并根据ACPID镇定规则建立了连续搅拌釜式反应器(continuous stirred tank reactor, CSTR)的ACPID控制系统.理论分析了ACPID控制系统的鲁棒稳定性和抗扰动鲁棒性.仿真结果表明了ACPID控制系统的有效性,在CSTR稳态调节控制领域具有重要的应用价值.     

基于PCS7的带搅拌釜式反应器的温度控制

带搅拌釜式反应器是一种常见的化工生产设备,为了保证生产安全、产品质量,需要对反应器的温度进行监控.针对釜式反应器的工艺特点和控制要求,研发了基于西门子PCS7系统的控制方案.讨论了控制系统相应的网络结构及硬件配置.提出了问歇反应温度控制分预热、升温、保温这三个阶段的控制策略.结果表明,控制方案使系统抗干扰能力和适应参数变化的能力都优于常规控制,达到了很好的控制效果.     

一种基于输出反馈的显式实时优化控制方法

针对一阶最优性必要条件跟踪法优化间隔较长的缺点, 提出一种基于输出反馈的显式实时优化方法. 对系统进行不同工况下的离线优化, 经函数拟合得到最优控制输入与输出变量的显式回归模型, 直接应用于实时优化, 避免了在线梯度估计. 研究一个连续搅拌釜式反应器的反应过程, 并对比两种方法的优化效果, 结果验证了所提出方法的实际使用效果

     

多重核学习非线性时间序列故障预报

针对非线性时间序列故障预报问题, 提出了多重核学习故障预报方法. 利用多重核学习可以减少支持向量的个数, 提高预测性能. 而且在多重核学习定义的混合核空间中运用减聚类能够提取正常原型. 最后, 将本文提出的方法应用于连续搅拌釜式反应器的故障预报, 仿真结果表明该方法能够提高故障预报的准确性与实时性.     

基于精确障碍罚函数的多单元极值搜索算法仿真研究

等温连续搅拌釜式反应器通常采用基于正弦激励信号的极值搜索算法进行控制,且需要针对输入流量和热能约束条件构造简单障碍惩罚函数,反应过程普遍存在着输出颤振、收敛速度慢、准确性低等问题。为此提出基于精确障碍罚函数的多单元极值搜索算法对多个相同反应器进行同步实时控制,并应用多单元极值搜索算法对连续搅拌釜式反应器进行仿真验证:该算法可有效提高收敛速度和准确性,消除了输出颤振。     

基于SIMATIC PCS7的带搅拌釜式反应器温度控制策略与仿真研究

该文以多功能过程与控制仿真实验系统（MPCE）中的带搅拌釜式反应器间歇反应过程为被控对象,设计了旨在确保反应温度变化的控制方案。控制方案集成了PID算法、模糊控制和专家系统。利用西门子SIMATIC PCS7过程控制系统进行了仿真研究。结果表明控制效果良好。     

双螺杆挤出机模具过渡和稳流段流场的数值模拟

采用Carreau模型描述熔体的黏度特征,使用POLYFLOW软件数值模拟了异向旋转双螺杆挤出机模具过渡和稳流段的三维等温流场。在不同的工艺参数下,分析比较了模具过渡和稳流段内的速度场、压强场、剪切速率场、剪切应力场以及黏度场。结果表明在模具过渡和稳流段内,螺杆的旋转是该聚合物熔体流变性能的最大影响因素,螺杆头对高黏度熔体的影响范围不大,只限于螺杆头的周围；进入稳流段后,在稳流段作用下熔体的流动逐渐变得稳定均匀；在本文讨论的转速和流量范围内,转速和流量的增加,分别会在不同的区域使熔体受到的剪切速率和剪切应力明显地增大。研究结果为某企业设计双螺杆模具和优化工艺条件提供理论依据。     

多相流搅拌器流场数值模拟软件

为对搅拌器多相流体间的最终乳化结果进行模拟,结合FLUENT与ANSYS软件,以VB为前台程序开发搅拌器流场数值模拟软件.用VB开发用户交互界面,通过后台调用ANSYS的APDL完成前处理模块,实现搅拌器叶片、筒体的建模,网格划分和组元创建;通过后台调用FLUENT运行日志文件实现流体流场仿真运算与结果后处理,并以图形...     

Flow over a membrane-covered,fluid-filled cavity

The flow-induced response of a membrane covering a fluid-filled cavity located in a section of a rigid-walled channel was explored using finite element analysis. The membrane was initially aligned with the channel wall and separated the channel fluid from the cavity fluid. As fluid flowed over the membrane-covered cavity, a streamwise-dependent transmural pressure gradient caused membrane deformation. This model has application to synthetic models of the vocal fold cover layer used in voice production research. In this paper, the model is introduced and responses of the channel flow, the membrane, and the cavity flow are summarized for a range of flow and membrane parameters. It is shown that for high values of cavity fluid viscosity, the intracavity pressure and the beam deflection both reached steady values. For combinations of low cavity viscosity and sufficiently large upstream pressures, large-amplitude membrane vibrations resulted. Asymmetric conditions were introduced by creating cavities on opposing sides of the channel and assigning different stiffness values to the two membranes. The asymmetry resulted in reduction in or cessation of vibration amplitude, depending on the degree of asymmetry, and in significant skewing of the downstream flow field.     

低液位非满管流量校准及其测量影响因素分析

管道粗糙度和流体黏度对流量测量有一定影响,为校准流量并分析其影响因素,运用FLUENT仿真软件对管道粗糙度、流体黏度进行模拟.建立粗糙度-平均流速、黏度-平均流速模型,搭建实验平台,验证模型建立的准确性,即外置U形连通管结合高精度激光测距仪精确测量管道内流体液位高度,管道上方通气管结合流速仪精确测量管道内流体平均流速,通过体积流量计算公式得到流量值.实验结果表明,在液位低于0.1D时,流量测量误差小于0.85％;通过粗糙度-平均流速、黏度-平均流速模型得到的平均流速值进行流量计算,计算结果误差小于3.03％.实验验证了该方法的可行性和模型的可靠性,为低液位非满管流量测量领域的技术创新提供了依据和实验基础.     

Application of lattice Boltzmann method in free surface flow simulation of micro injection molding

The filling flow in micro injection molding was simulated by using the lattice Boltzmann method (LBM). A tracking algorithm for free surface to handle the complex interaction between gas and liquid phases in LBM was used for the free surface advancement. The temperature field in the filling flow is also analyzed by combining the thermal lattice Boltzmann model and the free surface method. To simulate the fluid flow of polymer melt with a high Prandtl number and high viscosity, a modified lattice Boltzmann scheme was adopted by introducing a free parameter in the thermal diffusion equation to overcome the restriction of the thermal relaxation time. The filling flow simulation of micro injection molding was successfully performed in the study.     

火电SCR脱硝系统混合与均流CFD仿真

火电烟气脱硝系统能否达到高脱硝率与低氨气逃逸率,很大程度上取决于进入脱硝反应器之前烟气中的氮氧化物与还原剂氨气混合均匀程度和烟气速度分布。为此,需在脱硝反应器之前的烟道内安装烟气-氨混合器、导流板均流装置。采用计算流体力学仿真软件对烟道中的流态进行了仿真,结果表明,格栅型混合器的使用能够增强气体径向混合,改善烟气与氨气混合的均匀程度;在烟道转弯处加入导流板可以明显减少出口速度分布偏差。所用计算流体力学仿真软件可以给出烟道内任意位置的速度和浓度可视化输出,在经过流态模型实验的验证后,这些信息可以成为烟道内混合与均流装置优化设计的依据。     

Evaluation of passive mixing behaviors in a pillar obstruction poly(dimethylsiloxane) microfluidic mixer using fluorescence microscopy

The rapid mixing of fluids passing through a microfluidic channel is very important for various applications of microfluidic systems. It has been a great challenge to achieve highly efficient mixing in a microfluidic system because it is very difficult to generate turbulence in a submillimeter-size channel at low Reynolds numbers (Re). In this paper, we fabricated a pillar obstruction microfluidic mixer and evaluated its mixing efficiency at various flow rates. The mixing behavior of confluent streams was estimated using a fluorescence microscope. Three different sets of miscible solutions (phosphate-buffered solution, gold nanocolloids and 20% glycerol), with Rhodamine 6G aqueous solution, were used as sample laminar flows. According to our experimental results, the pillar obstruction microfluidic mixer shows an excellent mixing performance in the low Re range. Here, the mixing performance was strongly dependent on the characteristic viscosity changes of different sets of miscible solutions. The pillar obstruction microfluidic mixer designed here is expected to benefit a wide range of lab-on-a-chip applications because fabrication is very simple and the mixing efficiency is excellent at low Re.     

A study on the novel micromixer with chaotic flows

This paper presents the novel micro mixer with chaotic flow using coupling between Lorentz force and the moving force of the electric charge in an electric field. Rapid mixing is essential for μ-TAS technology, but is often difficult to achieve it at low Reynolds numbers in micro-systems. Although it is effective to mix with a stirrer for rapid mixing in a general macro-system, it is very difficult to fabricate it in a microsystem. Because the chaotic flow plays a role as a stirrer in a mixing chamber, the novel mixer is expected to mix more rapidly than existing micro mixers. The mixer not only has a simple structure compared with existing ones but also is able to achieve high mixing efficiency in spite of low power consumption. In order to estimate the efficiency for each mixer, the analytical expression and the computer simulations are performed. The results about the flow directions and the experimental results with mixing visualization are presented. Through the comparison with the mixing experiment using the diffusion process, we confirm that the proposed mixer with a simpler structure is able to achieve higher mixing efficiency.     

A magnetic microstirrer and array for microfluidic mixing

We report the development of a micromachined magnetic-bar micromixer for microscale fluid mixing in biological laboratory-on-a-chip applications. The mixer design is inspired by large scale magnetic bar mixers. A rotating magnetic field causes a single magnetic bar or an array of them to rotate rapidly within a fluid environment. A fabrication process of the magnetic bar mixer is developed. Results of fluid mixing in micro channels and chambers are investigated using experimental means and computer-aided fluid simulation.     

Behavior of micro-polar flow due to linear stretching of porous sheet with injection and suction

The boundary layer flow of a micro-polar fluid due to a linearly stretching sheet is investigated. The influence of various flow parameters like ‘suction and injection velocity through the porous surface’, ‘viscosity parameter causing the coupling of the micro-rotation field and the velocity field’ and ‘vortex viscosity parameter’ on ‘shear stress at the surface’, ‘fluid velocity’ and ‘micro-rotation’ are studied. The governing equations of the transformed boundary layer are solved analytically using homotopy analysis method (HAM). The convergence of the obtained series solutions is explicitly studied and a proper discussion is given for the obtained results. Comparison between the HAM and numerical solutions showed excellent agreement.     

Quantification of the performance of chaotic micromixers on the basis of finite time Lyapunov exponents

Chaotic micromixers such as the staggered herringbone mixer developed by Stroock et?al. allow efficient mixing of fluids even at low Reynolds number by repeated stretching and folding of the fluid interfaces. The ability of the fluid to mix well depends on the rate at which ??chaotic advection?? occurs in the mixer. An optimization of mixer geometries is a non-trivial task which is often performed by time consuming and expensive trial and error experiments. In this paper an algorithm is presented that applies the concept of finite-time Lyapunov exponents to obtain a quantitative measure of the chaotic advection of the flow and hence the performance of micromixers. By performing lattice Boltzmann simulations of the flow inside a mixer geometry, introducing massless and non-interacting tracer particles and following their trajectories the finite time Lyapunov exponents can be calculated. The applicability of the method is demonstrated by a comparison of the improved geometrical structure of the staggered herringbone mixer with available literature data.