涡轮桨搅拌槽内混合过程的数值模拟

文中采用FLUENT软件对六直叶涡轮桨搅拌槽内的混合过程进行了数值模拟,选用多重参考系法(MRF)及标准kε模型,将速度场与浓度场方程分开进行求解,所得的混合时间的模拟结果与实验值相吻合。同时用计算机流体力学(CFD)方法研究了不同的加料点、监测点位置及操作条件对混合时间的影响规律,模拟结果表明:混合过程主要由搅拌槽内的流体流动所控制,混合时间与加料点及监测点位置密切相关。研究结果对于工业搅拌反应器的优化具有一定的参考意义。     

多层桨搅拌槽内的宏观混合特性

在直径为0.476 m的搅拌槽内,采用电导法测定搅拌槽内单层桨和多层桨体系的混合时间。对于单层桨体系,在相同的搅拌输入功率下,不同类型的径向流桨和轴向流桨具有相同的混合时间。对于窄叶翼型CBY搅拌桨,在相同的搅拌输入功率下,单层、双层以及三层CBY搅拌桨的混合时间基本相同;而对于六直叶涡轮桨DT-6,在相同的搅拌输入功率下其混合时间随桨叶层数的增加而加长;多层CBY桨的混合时间远低于多层DT-6搅拌桨的混合时间。     

2种型式搅拌桨用于工业规模搅拌釜内假塑性流体混合过程的数值模拟

用CFD技术研究了最大叶片式桨和三层六直叶涡轮桨的在大高径比工业规模搅拌釜中流体力学行为,以黄原胶溶液为研究体系,重点考察了功率特性、死区分率、剪切性能和混合时间等流体动力学性能.结果表明:2种搅拌桨的功耗与转速成正比,死区与转速成反比;随着雷诺数增加,釜内平均剪切速率增加.工业规模搅拌釜中,最大叶片式桨搅拌流场呈双循环流型,三层六直叶涡轮桨在每个桨叶叶端分别形成上下2个小循环.在相同单位体积功耗下,最大叶片式桨的混合时间相对于三层六直叶涡轮桨较短.     

9种搅拌器以水为介质混合时间的测定

在7 L玻璃搅拌釜中,以水为实验介质,在无挡板条件下采用温差法和比色法,考察了9种搅拌器的混合时间.结果显示:在实验转速范围内,所有搅拌器随着转速的升高,混合时间缩短.对6种小浆叶(d/D=0.5)搅拌器而言,双层六直叶开启涡轮式桨叶的混合时间最长,单层四斜叶T型桨A的混合时间最小;在单层搅拌器中,六直叶开启涡轮式搅拌器的混合时间最长;对大桨叶(d/D=0.8)搅拌器而言,框式混合时间最长,单层二斜叶T型桨B最短;温差法和比色法两者测定结果趋势基本一致.     

运用CFD研究钟摆式搅拌的混合效率

设计了一种钟摆式搅拌槽,对槽内流场和混合过程进行了数值模拟,分析了槽内流体的流动特性及加料方式对混合效果的影响。并对混合效率进行了评定.结果表明:钟摆式搅拌槽内桨叶上方区域的混合比桨叶下方要好;考察加料位置的影响时,自由液面加料的混合效果优于底部加料;整体来讲,自由液面加料时钟摆式搅拌槽的混合效率比较高,与三窄叶翼形搅拌桨相接近,槽底部加料时的混合效率要低一些,与六直叶圆盘涡轮桨相当.     

搅拌设备内流场的数值研究

利用滑移网格法计算了六直叶Rushton涡轮搅拌设备内的流场。考察了计算流体力学(CFD)模拟搅拌设备流场的预测能力,分析了搅拌桨叶端及附近区域的流动行为。结果表明：CFD计算的时均速度与实验结果一致,CFD技术与实验手段可相互补充;搅拌桨叶片端部的速度分布并非关于叶片高度的中心位置严格对称,搅拌设备的流场结构并非完全由搅拌桨的行为决定;六直叶Rushton涡轮叶端附近区域最大径向速度点与最大切向速度点不在同一个位置,径向速度在叶端附近区域有一个流动发展的过程。     

涡轮桨搅拌槽内混合过程的大涡模拟

在FLUENT 6.1软件平台和网络并行计算硬件平台上,采用大涡模拟(LES)的方法对涡轮桨搅拌槽内的混合过程进行了数值模拟。利用滤波函数对N av ier-Stokes方程进行空间滤波,对大尺寸的涡直接进行求解,而被滤掉的比网格小的旋涡通过Sam agorinsky-L illy亚格子模型求解,对搅拌桨区域采用滑移网格技术。结果表明:大涡模拟对尾涡的预报优于雷诺平均(RAN S)方法,混合时间以及示踪剂响应曲线模拟结果和实验结果吻合较好,且优于RAN S方法。大涡模拟方法为准确预测搅拌槽内湍流流动的非稳态及周期性脉动特性提供了一种有效的工具。     

搅拌槽内不同桨型组合的气-液分散特性

在直径为0.476m的椭圆底搅拌槽内,分别研究径向流桨（八弯叶涡轮CDT-8）组合、轴流式搅拌桨（四叶宽叶翼形WH桨）组合及混合流型组合桨（径向流的六叶半椭圆管盘式涡轮HEDT与三窄叶翼形桨CBY）的通气功率及气含率,并得到了相应的通气功率和气含率的经验关联式。结果表明：HEDT底桨配合CBY轴流桨的混合流组合桨的RPD值下降最少,轴向流组合次之,而径向流组合桨R_PD下降最多;在相同的通气搅拌功率下,在低通气量时,轴向流组合桨的气含率最高,在较高的通气流量时,混合流及径向流组合桨的气含率相当,均高于轴向流组合桨。文中的研究结果可为工业多层桨气-液搅拌槽/反应器的优化设计提供参考。     

三层桨搅拌槽内聚醚多元醇流场的LDV测量与数值模拟

采用流体力学软件(FLUENT),建立了两种三层桨搅拌槽的数值模拟模型,模拟聚醚多元醇(PPG)的流动特性,并与激光多普勒测速技术(LDV)测量数据进行比较。结果表明,选用多重参考系法(MRF)和Laminar模型计算结果与LDV测量值基本吻合。上、中层为四宽叶翼型上提桨(WHu),底层为六半椭圆管涡轮桨(6-HEDT),槽内"死区"少、高速率区分布多、搅拌功率损耗小、径向与轴向速率大,适用于PPG搅拌系统内。两种组合桨的周向速率均偏大,因而降低PPG的周向速率或提高轴向和径向速率,是改善PPG搅拌混合的关键。     

搅拌对箱式混合澄清槽流动性能的影响

针对当前混合澄清萃取槽存在的问题,提出了改进的新型混合澄清萃取槽.采用专业的流体力学数值模拟软件ANSYS/FLUENT,对新型萃取槽内流场情况进行了模拟研究.结果表明,在油水两相流速分别为0.22和0.11 m/s,混合室搅拌转速为800 r/min,澄清室搅拌转速为20 r/min时,与传统萃取槽相比,在搅拌作用下,新型萃取槽澄清室内桨叶附近的混合带更窄,两相分离效果更佳;混合室内桨叶上下方流场呈涡旋流,与六直叶涡轮桨搅拌特点相符.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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