新型同心双轴搅拌器功率与混合特性的数值模拟

基于同心双轴搅拌器的结构与运行特点,建立了兼顾其流动、混合过程的三维数学模型,并以过程工业应用较多的两种不同尺寸双层组合桨作为内桨、框式桨作为外桨构成的同心双轴搅拌器为研究对象,数值模拟了其在中高黏牛顿流体中同向及反向转动模式的功率特性、流场特性及混合特性。模拟结果表明,同向转动模式下,整个系统的搅拌功耗更小、混合效率更高;外桨功耗受内桨影响较大,一般随内桨转速的增大,恒速外桨的功耗同向转动时会减小、反向转动时会增大;对由桨式搅拌器构成的组合式内桨而言,当内桨直径与釜体直径之比为0.35左右时,相同Reynolds数下的单位体积混合能更小;中高黏牛顿流体中,同心双轴搅拌器的内桨采用上层六斜叶桨+下层六直叶桨的组合形式时更高效节能,仅在体系Reynolds数小于36时,上层二斜叶桨+下层二直叶桨的内桨组合形式才具有相对优势。     

同心双轴搅拌器气液分散性能的实验研究

针对气液搅拌操作形式单一的现状,将框式桨和Rushton桨组成的同心双轴搅拌器与黏稠体系中的气液分散操作相结合,实验考察了转动模式、内桨转速、通气量和体系黏度等因素对其气液分散性能的影响。结果表明,与单相黏稠体系中同向旋转模式下的功率与混合性能均占优不同,同心双轴搅拌器在反向旋转模式下的气液分散性能相对更好;外桨转速不变时,内桨转速从100增加到300 r·min~(-1),整体气含率提高94.3%,局部气含率也均有增大;通气量从0.4提高到1.2 m3·h~(-1),整体气含率提高了72.5%,但局部气含率和气泡尺寸的增大不显著;体系黏度增加,气泡在釜内的停留时间加长,整体气含率单调增加。作为影响搅拌釜气液分散性能的重要参数,转动模式、内桨转速和通气量的确定还必须兼顾系统的功耗与混合效率,并避免发生气泛。     

漂浮颗粒临界悬浮过程搅拌桨型优化研究

在中低黏度的牛顿流体中,通过机械搅拌将漂浮颗粒下拉进入液体中并实现固体溶解过程,在工业中有广泛应用。文中以黏度为60 m Pa·s的基础油为实验物系,对3种不同的固体胶块形式进行临界悬浮过程的研究,采用了5种不同桨型,2种不同操作方式,分别研究各种桨型的功率消耗、混合特性以及漂浮颗粒的临界下拉功率等参数。结果表明:为达到将漂浮颗粒下拉进入液相并进行高效混合的目的,推荐采用下压操作、功率准数较低的窄叶翼型轴流桨CBY,该组合桨相对于传统斜叶桨PBT、宽叶轴流桨WH及窄叶轴流桨MIG而言,临界悬浮条件下功率消耗低,功率消耗相同时混合时间短,即混合效率更高的优点,能够实现漂浮颗粒临界悬浮过程的高效搅拌目的。     

双轴异桨变速组合型搅拌器的轴功率与混合效率

本研究测定了齿盘(偏置)式、锚式、45°框桨式三种搅拌器和齿盘-锚式、齿盘-45°框桨式两种双轴异奖变速组合型搅拌器的功率(N~p～Re)曲线和它们在操作流域(以单桨计算,Re=63—600)内的混合效率。结果表明,在层流域至弱过渡流域,组合型各搅拌器的功率与组合前单个搅拌器的功率基本相同;但在强过渡流域至湍流域,其功率计算要进行修正。组合搅拌器的功率是各搅拌器功率的迭加。效率较低的齿盘-锚式组合搅拌器比效率较高的齿盘式节能50％。齿盘-45°框桨式组合搅拌器的混合能是60°双层斜桨式的22％;是MIG型的50％。双轴异桨变速组合型搅拌器是一种值得开发的操作弹性宽、效率高和能耗低的搅拌设备。     

酯化反应器内搅拌器的优化设计

搅拌功率和循环流量是考察搅拌桨性能和搅拌槽内混合效果的两个重要参数。作者在直径为5 0 0 m m和 80 0 mm的带导流筒的搅拌槽内 ,试验测试了现工业生产中酯化反应器内的搅拌桨的循环流量准数和功率准数 ,并根据工艺要求优选出以 CBY螺旋浆与直叶透平桨组成的双层浆式搅拌器 ,该搅拌桨比现工业用桨在消耗相同功率的条件下能产生更大的循环流量     

双层涡轮桨偏心搅拌槽内的宏观不稳定性研究?

采用分离涡模型和 PIV 实验测试方法研究了双层桨偏心搅拌槽内的宏观不稳定性,通过对速度时间序列的频谱分析,讨论了搅拌桨的安装方式(单轴双桨和双轴双桨)及转动方向对宏观不稳定频率的影响,并与单层桨偏心搅拌进行了对比。研究发现,双层桨偏心搅拌的宏观不稳定频率稍低于单层桨偏心搅拌;搅拌桨安装方式及转动方向对双层桨偏心搅拌的宏观不稳定频率有明显影响：双轴双桨偏心搅拌时的频率稍高于单轴双桨偏心搅拌,搅拌桨反向旋转时的频率又高于同向旋转。     

双层涡轮桨偏心搅拌槽内的宏观不稳定性研究

采用分离涡模型和PIV实验测试方法研究了双层桨偏心搅拌槽内的宏观不稳定性,通过对速度时间序列的频谱分析,讨论了搅拌桨的安装方式(单轴双桨和双轴双桨)及转动方向对宏观不稳定频率的影响,并与单层桨偏心搅拌进行了对比。研究发现,双层桨偏心搅拌的宏观不稳定频率稍低于单层桨偏心搅拌;搅拌桨安装方式及转动方向对双层桨偏心搅拌的宏观不稳定频率有明显影响:双轴双桨偏心搅拌时的频率稍高于单轴双桨偏心搅拌,搅拌桨反向旋转时的频率又高于同向旋转。     

双轴表面更新型搅拌釜中高粘牛顿流体与非牛顿流体的功耗

实验测定了双轴表面更新型卧式釜中采用三种不同形式的搅拌桨、多种桨间距、广泛的粘度范围内牛顿流体和非牛顿流体的功率特性;统一关联了牛顿流体与非牛顿流体的搅拌功耗,得到:N_PRe=C(l/D_f)~(-1)(V_L/V~*)~D式中的C、D是搅拌桨的结构参数.实验结果还表明,该装置的Metzner常数是转速的函数.     

固-液搅拌槽的分散性能

在直径为0.478 m的立式搅拌槽中,采用高岭土和水为物料,比较了四斜叶、六直叶涡轮等8种桨的固-液分散性能及搅拌功率(P)、桨组合形式对分散性能的影响规律. 结果表明,8种桨中分散效果最好的是六直叶涡轮桨和四斜叶桨,分散速率最快的是两叶CBY桨;分散速率与P1.08成正比;分散前期,搅拌功率增加,相对分散效果Y随之提高,当Y达到0.999以上,提高搅拌功率对搅拌效果几乎不起作用;采用分散速率较快(两叶CBY桨)与分散效果较好(四斜叶桨)的双桨组合,更适于连续操作过程.     

机械搅拌用于水处理中混凝过程的研究

以机械搅拌用于水处理中混凝过程为研究对象 ,在 0 .75 m× 0 .75 m× 1 m方形搅拌槽中 ,利用配制的两种污水 ,以 Al2 ( SO4 ) 3· 1 8H2 O为絮凝剂 ,采用三种不同直径的轴流式 CBY型搅拌桨 ,分别得出适用于快速混合过程及絮凝过程的机械搅拌操作参数 :( 1 )对于快速混合过程 ,搅拌桨直径增加 ,絮凝剂混匀所需输入功率增大 ;( 2 )对于三级絮凝过程 ,三级絮凝搅拌桨叶端线速度之比为3∶ 2∶ 1 ,第一级叶端线速度的适宜范围为 :1 .5～ 1 .8m/s;输入功率相同时 ,不同直径搅拌桨的絮凝效果相当 ;对于 CBY型搅拌桨 ,离底距离对絮凝效果影响不大。     

一种新型搅拌桨多相混合性能研究

提出了一种新构型的搅拌桨一错位桨,并以空气-水-石英砂三相体系为研究对象,与传统的径流桨(Rushton桨)和轴流桨(斜叶桨)在功率消耗、混合时间、气体循环方面进行了比较.结果表明,错位桨相对于传统Rushton桨,功率消耗降低.适应气速范围广,轴向混合能力明显提升;在同等条件下与斜叶浆相比,气体分散能力强,混合时间少.这种新型桨能克服径向流叶轮在轴向混合方面能力的缺陷,有较好的潜在工业应用价值.     

Influence of impeller diameter on overall gas dispersion properties in a sparged multi-impeller stirred tank☆

The impeller configuration with a six parabolic blade disk turbine below two down-pumping hydrofoil propellers, identified as PDT + 2CBY, was used in this study. The effect of the impeller diameter D, ranging from 0.30T to 0.40T (T as the tank diameter), on gas dispersion in a stirred tank of 0.48 m diameter was investigated by experimental and CFD simulation methods. Power consumption and total gas holdup were measured for the same impeller configuration PDT + 2CBY with four different D/T. Results show that with D/T increases from 0.30 to 0.40, the relative power demand (RPD) in a gas–liquid system decreases slightly. At low superficial gas velocity V_S of 0.0078 m·s^-1, the gas holdup increases evidently with the increase of D/T. However, at high superficial gas velocity, the systemwith D/T=0.33 gets a good balance between the gas recirculation and liquid shearing rate, which resulted in the highest gas holdup among four different D/T. CFD simulation based on the two-fluid model along with the Population Balance Model (PBM) was used to investigate the effect of impeller diameter on the gas dispersion. The power consumption and total gas holdup predicted by CFD simulation were in reasonable agreement with the experimental data.     

多层组合桨搅拌槽内气-液分散特性的研究

在直径为0,476m的椭圆底搅拌槽中,采用由六叶半椭圆管叶盘式涡轮桨(HEDT)及四叶宽叶翼型桨的上提(WHU)及下压(WHD)操作组合的六种不同的三层桨,研究了气-液两相体系中的通气功率变化及气含率特性,获得不同桨型的通气搅拌功率及气含率的关联式;结果表明,底桨为HEDT的组合桨通气功率下降幅度最小,相同输入功率时气含率最高,其次为WHD,WHU为底桨时气液分散性能最差。因此,适用于气液两相操作的优化组合桨应以HEDT为底桨。此研究结果可为工业用多层组合桨气液搅拌反应器的设计提供参考。     

搅拌槽内多层组合桨对液-液分散特性的影响

以水-煤油及水-环己烷为体系,研究Rushton涡轮桨(RT),半椭圆管涡轮(HEDT)及翼形轴流式桨(CBY)的6种不同组合桨的液-液分散特性。测定了不同输入功率时分散相体积分率沿轴向及径向的分布。结果表明:当搅拌槽内液位与槽径之比达1.5,在相同输入功率时,三层桨的液液分散性能优于两层桨,功率准数较低的CBY组合桨在输入功率0.8kW/m~3时,槽内的轴向及径向分散相体积分率达到稳定的均匀分布。而功率准数较大的RT组合桨需要在输入功率1.8kW/m~3才能达到槽内分散相的均匀分布。     

LIQUID DISPERSION MECHANISMS IN AGITATED TANKS: PART II. STRAIGHT BLADE AND DISC STYLE TURBINES

The dispersion of oil in water in an agitated vessel was studied for two types of radial discharge impellers, straight blade and disc style turbines. Two different dispersion mechanisms, ligament stretching and turbulent fragmentation, were observed to occur in the vortex systems of the impeller discharge. Although these two dispersion mechanisms were similar to pitched blade turbine performance, differences in the velocity magnitudes and vortex interactions were observed with the radial flow impellers. The ligament stretching mechanism was observed between the vortex formation regime and the transition to the fragmentation regime. The turbulent fragmentation mechanism was observed only in highly turbulent flow.

Blade thickness was found to influence the ligament stretching mechanism. A thin blade on the straight blade turbine created higher vortex velocities and smaller drop sizes than a thick blade for the same tip speed and processing time. The consequences of this blade thickness effect could be significant when laboratory data are used to design large process equipment for liquid-liquid dispersion.     

转子构型对炭黑分散性及胶料力学性能的影响

主要研究了不同转子构型对炭黑分散性及胶料力学性能的影响。实验表明，在相同混炼条件下，6棱同步转子混炼的胶料获得最好的炭黑分散性，4棱转子的次之，在3组2棱同步转子中，2棱功能转子的混炼效果最好。说明通过改变转子构型，可有效地改善混炼胶中炭黑的分散性，提高胶料的力学性能。     

SV型静态混合器分散性能研究

以水－煤油为介质，在不同的流速下，通过高速照相的方法，研究了１５种不同的苏尔士静态混合器（ＳＶ型）的分散性能，分析了苏尔士静态混合器结构参数对分散性能的影响，得出液滴直径－流速关系曲线，并拟合成数学关系式。     

Effect of agitation and aeration on gas dispersion efficiency in coaxial mixers containing yield-pseudoplastic fluids: Experimental and numerical analysis

Aerated stirred vessels are commonly employed to enhance gas dispersion. However, the associated high energy consumption is a challenging feature, particularly when dealing with complex non-Newtonian fluids. Coaxial mixers comprising a central impeller and a close-clearance impeller have emerged as an energy-efficient alternative that effectively intensifies gas dispersion. Hence, the objective of this study is to investigate the effect of aeration and agitation on the gas dispersion effectiveness of a coaxial mixer containing a yield-pseudoplastic fluid. An anchor-pitched blade turbine was employed to disperse air into a 1 wt.% xanthan gum solution, and the analysis primarily focused on characterizing the gas holdup and fluid flow behaviour. Gas holdup data were obtained experimentally using electrical resistance tomography (ERT), while computational fluid dynamics (CFD) simulations provided a detailed analysis of fluid flow patterns within the coaxial mixer. The rotational speed of the impeller exhibited a non-monotonic effect on the gas holdup, and a significant influence of the interaction between variables was identified. For instance, the experimental data showed that the aeration effect varied with the anchor speed. Nevertheless, the variables' interaction effect was explained by the change in flow pattern observed numerically. Furthermore, the CFD results demonstrated that high gas holdup does not necessarily indicate intensified mixing. Therefore, combining experimental data and numerical simulations enables a more accurate characterization of mixing performance. These findings contribute to the understanding and improvement of mixing performance in such a complex system, which is crucial for designing efficient operations.