六直叶开启涡轮式搅拌器的二维数值模拟

由于搅拌过程中流场的复杂性,选用何种型号的搅拌器从而提高搅拌效率、降低能耗是搅拌设计中的关键。本文借助Fluent软件分析六直叶开启涡轮式搅拌器的桨叶直径、转速对搅拌的影响,并对比了在同一工况下平直叶圆盘涡轮式搅拌器和六直叶涡轮搅拌器的搅拌效果。     

新型搅拌器结构设计及其关键参数对性能的影响

设计了一种新型带包圈型六叶平直叶桨式搅拌器,建立其结构和流场模型,利用数值模拟方法对搅拌容器内部的固-液两相流场进行模拟计算,通过分析液相速度矢量图和固含率云图,研究关键参数对新型搅拌器的性能影响.结果 表明:搅拌器包圈高度、搅拌转速、安装高度和桨叶直径对搅拌器的混合效果具有重要影响,在搅拌器选型和搅拌器工作时,选择合...     

圆盘涡轮式搅拌器的搅拌性能比较分析

在椭圆封头搅拌槽中根据行业标准建立了4种圆盘涡轮式搅拌器的几何模型,利用标准k-ε湍流模型和多参考系(MRF)方法,研究了叶片形状、搅拌速度、旋转方向和流型转变对搅拌功率、排出流量、泵出效率和剪切速率的影响。结果表明：叶片形状对功率、排出流量、泵出效率和流型转变的临界安装高度均有影响;径向流条件下,泵出效率排序为圆弧叶(反)>弯叶(正)>箭叶(反)>圆弧叶(正)>平直叶>箭叶(正)>弯叶(反);流型由径向流转变为轴向流后,搅拌功率及径向排出流量均下降。对标准搅拌器的性能评估为工业搅拌设备的选型和设计提供了参考依据。     

6种常规搅拌器的剪切性能研究

不同搅拌工况下剪切性能的需求是选用搅拌器的一个重要指标,文中基于对常规的6种搅拌器流场的CFD模拟,计算了搅拌器各自的剪切性能量纲一数C_3,分析了搅拌流场中剪应力的累计概率分布及统计平均结果。二者对比发现:从宏观平均效果上看,搅拌器剪切性能满足直叶桨>斜叶桨,圆盘涡轮>开启涡轮>桨式;而剪应力极大值影响作用则是直叶圆盘涡轮>斜叶圆盘涡轮>直叶桨式>斜叶开启涡轮>直叶开启涡轮>斜叶桨式。因此,对剪切作用敏感的搅拌过程,在采用常规的搅拌器剪切性能评价的基础上,还需要充分考虑搅拌流场中剪应力极大值的影响,合理选用搅拌器。     

液下加氢搅拌系统的设计改进

气、液、固三项化合反应中有90%以上的搅拌反应釜选用自吸式搅拌器,它可以完成气相在液相的分散与吸收,自吸式搅拌器可以将气相均匀分布到搅拌器周围的液相中,但是自吸搅拌器只是将气体引入液相,要靠具有轴流推力或径向推力的其他搅拌器来完成流体混合,而用于气-液分散的直叶圆盘涡轮在气液两相操作时,叶片后方有气穴使其泵送能力降低。对自吸式搅拌器和直叶圆盘涡轮的结构提出改进方案并提出一套效果很好的液下加氢组合搅拌方案。     

疏水缔合聚丙烯酰胺溶解槽内流动特性的数值模拟

将疏水缔合聚丙烯酰胺AP-P4溶解过程划分为三种混合状态(搅拌槽中刚加入聚合物颗粒、溶胀刚结束和溶解完成),并采用计算流体力学方法分别对采用二斜叶桨式搅拌器XJD和新型翼型上推式搅拌器KCXU时溶解聚合物AP-P4的三种混合状态的流动进行了数值模拟,获得了两种搅拌器槽内的流场特性和XJD、KCXU搅拌器不同状态时的循环...     

基于ANSYS的聚氨酯发泡机搅拌器结构设计及优化

为解决现有聚氨酯发泡机原料搅拌器因笨重而引起功率和材料的浪费、搅拌效率低等问题，采用响应面分析法对聚氨酯料罐内搅拌器进行结构轻量化设计。设计了一种四叶平直叶开启式涡轮搅拌器，以其搅拌轴和搅拌叶片为主要研究对象。首先，将UG＿NX建立的几何结构导入ANSYS中对两者进行有限元静力学分析。根据搅拌器的实际工况，分别施加力与载荷后，求解得到变形图和等效应力图。其次，在静力学分析的基础上对叶片进行响应面分析。以质量最小为优化目标，叶片的厚度和宽度为设计变量，叶片在对应的力与载荷条件下所受的应力与变形为约束条件，最后求解得到质量最小且满足应力、应变条件下所对应的最优结构尺寸方案。最后，为避免搅拌轴发生共振，对搅拌轴进行模态分析，得到其前六阶的振型和固有频率。最终仿真结果表明，叶片质量减少为原来的31%，且最大变形仅为0.035 mm，最大等效应力为7.52 MPa。证明采用响应面分析法对搅拌轴及叶片的结构进行轻量化设计能够满足强度要求。     

烷基苯磺酸盐贮缸搅拌器的改革及减振器装置

我国年产万吨合成洗涤剂的生产厂,设计的烷基苯磺酸盐(LAS,以下简称磺酸盐)存缸直径2800毫米,高3200毫米,容积20立方米,共计三个,总容积为60立方米。原设计选用两片平直的桨叶片,桨叶片直径为d=1200毫米,共二组。这种搅拌器的圆周速度以1．5~3米/秒比较合适,适用于搅拌粘度较小(一般10~20厘泊)的物质较佳。而磺酸盐缸高度为3200毫米,容积内料液层比较高,加之磺酸盐粘度一般为360~400厘泊,直桨叶片随同转轴回转,形成搅拌器桨叶和磺酸盐介质之间的相对运动,而产生     

偏心射流搅拌强化1,3-二氯-2-丁烯的氯化行为

1,3-二氯-2-丁烯(DCB)的氯化过程同时存在加成反应、取代反应和连续反应,DCB与氯气混合不均匀和反应热移除效果不佳会降低取代氯化的选择性。搅拌槽内流场分布特征与流体的混合效果、化学反应的转化率和选择性等密切相关,调控流场结构有助于强化DCB的氯化行为。文中结合搅拌器专用计算流体动力学软件MixSim 2.0.2,模拟了在偏心射流条件下4 cm二直叶桨式搅拌器、4 cm斜叶圆盘搅拌器和5 cm斜叶圆盘搅拌器槽内的流场分布特征,并进行了DCB氯化实验。研究表明:偏心射流能改变流场分布,控制流场的拟序结构,强化混合效果。在偏心斜射流的条件下,5 cm斜叶圆盘搅拌器的氯化效果较优,能够使DCB氯化的主产物2,3,4-三氯-1-丁烯(TCB)的收率提高到87.9%。     

弯叶自吸式搅拌器功率准数的研究

通过对直叶和弯叶自吸式搅拌器的对比实验研究,测绘功率曲线,确定它们在湍流时的功率准数。通过对搅拌器中的流体进行运动分析和桨叶进行受力分析,利用永田算法计算功率准数,将实验数据和理论计算进行对比,引入修正参数,为弯叶自吸式搅拌器的关联式计算方法提供依据。     

Scaling factors in granular flow—analysis of experimental and simulations results

The relationship between the design of powder mixers and their performance is of crucial importance for many industrial processes and yet is not well understood. Here the flow patterns generated by an agitator carrying a long flat blade were compared to those generated by a single ploughshare using positron emission particle tracking and DEM. The performances of these agitators were also assessed against those of multi-blade and multi-plough agitators. The powder flows created by the different designs had some qualitative similarities. Indeed, all the agitators were shown to generate a loop of circulation below the free surface of the bed. The radial support of each mixing element was also observed to act as a separatrix for the axial flow, leading to the formation of a loop of circulation on each side of the mixing elements, thus inhibiting axial convection of material. The single-blade agitators, be the flat blade or the plough, were found to induce a pulsing regime, this feature being also observe with the multi-blade agitators but with a lesser amplitude. For moderate agitator frequencies of rotation where inertial effects are negligible, fundamental characteristics of the flow patterns extracted from power spectra of axial displacements could be scaled with the number of blade passes.     

组合桨搅拌器的宏观混合特性

分别以浓度为１％，２％，３％，３．５％的羧甲基纤维素溶液为实验，采用测温法，测定了正交双层三角桨－单螺带桨，正交双层三角桨－内外单螺带桨．锚式桨－三叶推进器．锚式桨－内外单螺带４种组合桨拌器的宏观混合时间，无量钢数Ｃ１，Ｃ２，Ｃ３，Ｃ４综合评判了它们的宏观混合性能，实验证明，前２种组合桨搅拌器在不同流域内都使搅拌介质达到良好的宏观混合，且功率消耗低，混合效率高，具有明显的节能优势，对搅拌变粘度体系     

用于腈纶废丝溶解的往复回转式搅拌器的研究

介绍往复回转式搅拌器的特性 ,研究三角形截面往复回转式搅拌器的桨叶尺寸、釜体尺寸、桨间距、搅拌转速和搅拌功率之间的关系 ,通过对单向回转扭矩法测得的功率与日本扭矩法比较 ,验证了往复回转功率表法的可靠性 ,并进行了模拟腈纶长丝搅拌实验 ,长丝长度达釜径的 18倍 ,仍不缠结 ,当加入的长丝束质量比为 11.8%时 ,搅拌功率约增加 1.2倍     

Advantages of the hollow (concave) turbine for multi-phase agitation under intense operating conditions

The mixing literature on hollow blade turbines (HBTS), for operation in fully turbulent flow, is reviewed and compared with the results of our own studies. The SCABA 6SRGT is shown to have an almost identical pumping rate to a disc turbine, when compared at the same diameter and specific power. An equation is proposed for the effect of scale and blade geometry on the power number of a range of concave hollow blade agitators. The “flooding-loading” condition is revisited. It is found that, when compared at conditions above the minimum Froude number required to disperse gas, the HBT designs are as energetically efficient as Rushton turbines for dispersing gas. If we compare them on an “ungassed” power basis, as is the usual literature case, then the HBT is more efficient because of their ability to disperse gas without significant loss of power. The much lower power number resulting from the streamlined blade design of the HBTs also ensures that they achieve the minimum Froude number required to disperse gas at a much lower power than a RT. A simple method to avoid “flooding” for radial turbines, based on this work, is proposed. Under fully loaded conditions the hollow blade turbines will handle high gas rates without significant loss of power and this ability is a function of the degree of streamlining. For the suspension of high levels of solids the D=T/2 hollow blade turbines, at a clearance of T/4, are found to be amongst the most efficient agitators especially under gassed conditions, where almost no effect of gassing on the just suspension speeds were noted.     

Experimental Study of Influence of the Impeller Spacing on Flow Behaviour of Double‐Impeller Stirred Tank

The flow fields in the stirred tank with three different kinds of combined double‐impeller agitators: disc turbine + disc turbine (DT‐DT, radial impeller), pitched blade turbine + pitched blade turbine (PTD‐PTD, axial impeller) and pitched blade turbine + disc turbine (PTD‐DT), were investigated in detail by using laser Doppler anemometry. The two‐dimensional mean velocity field and the distribution of turbulence intensity were obtained for different impeller spacings. The experimental results show that the impeller spacing has a significant influence on the flow field. To improve flow homogeneity and agitator efficiency, the appropriate impeller spacing should be in the range of 1/2 to 2/3 of the tank diameter.     

Mixing in the transition flow regime with helical ribbon agitators

The effects of the non-Newtonian properties on the effective deformation rate, mixing and circulation times and flow behaviour have been investigated in the transition flow regime of mixing systems. Based on the equivalent Couette flow, three models are proposed and are shown to predict similar and drastic increases of the effective deformation rate with the impeller rotational speed in the transition regime. The predictions are shown to fit very well data obtained for various non-Newtonian fluids mixed with helical ribbon agitators, and with literature data for anchor, blade turbine and flat disc agitators. The elasticity along with shear-thinning properties appear to have slight effects on the dimensionless mixing and circulation times in the transition regime, whereas their effects in the laminar regime are quite drastic, as reported by others.     

新型搪玻璃搅拌桨搅拌特性数值模拟及实验研究

采用CFD方法模拟了具有相同桨径、不同桨叶折角和叶宽结构的6种新型搪玻璃搅拌桨的搅拌特性。考察了挡板、桨叶离底高度对釜内流场的影响,基于此分析了桨叶折角、叶宽对速度分布的影响。对模拟得到的搅拌功率和混合时间进行了实验验证,并与传统搪玻璃桨式搅拌器进行比较。结果表明：①新型桨叶在加挡板且桨叶离底高度为450 mm时,搅拌效果最佳;②随桨叶折角、叶宽的增大,桨叶区轴向、径向和切向速度均呈增大趋势,当桨叶折角为45°、叶宽为95 mm时,釜内混合效果最好;③随转速增大,搅拌功率呈增大趋势,混合时间呈减小趋势,新型桨明显比传统桨混合性能好,桨叶折角为30°、叶宽95 mm时功率消耗最低,桨叶折角为35°、叶宽95 mm时混合时间最短。     

Studies on transfer processes in mixing vessels: hydrodynamic of the modified Rushton turbine agitators in gas—liquid dispersions

The modified blade turbines are attractive alternatives to the standard Rushton turbine as they do not require any modification in the electrical engine motor and drive assemblies, are simple to manufacture, have a reduced power consumption and have a greatly increased gas-handling capacity before flooding.The modified blades were obtained through increase in the blade height of the Rushton turbine simultaneously with perforation of the blade surface. The filled surface of the modified blade is equal to the blade surface of the standard Rushton turbine.Power dissipation and hydrodynamic regimes using standard and modified Rushton turbine agitators positioned singly or doubly on the same shaft, in a gas—liquid system, were investigated.The TP3 modified turbine with the surface fraction S_G/S_C of the perforation equal to 0.353 is optimum on the basis of the power consumption and of the gas-handling and dispersing capacity.     

Rheological phenomena during the polymerization of styrene in a stirred tank

An experimental study of the bulk polymerization of styrene has been carried out. The rate of polymerization, molecular weight, and flow patterns around agitators as a function of conversion have been observed. The rate data are interpreted in terms of free-radical polymerization kinetics. Duerksen and Hamielec's modified termination rate constant and initiator efficiency relations are generally consistent with our data. The flow patterns were interpreted in terms of the mechanics of viscoelastic liquids and observations for nonreacting systems. Specifically, at low conversions for spheres and similar agitators, the flow patterns are dominated by centrifugal forces with fluid drawn in at the poles and expelled at the equator for spherical agitators. At higher conversions, normal stresses interact with the centrifugal forces causing segregated secondary flow regions adjacent to the sphere. At very high concentrations, normal stresses dominate, yielding Weissenberg effects.