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。     

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.     

卧式双轴T型搅拌器在非牛顿流体中的搅拌功率特性

考察了卧式双轴Ｔ型搅拌在非牛顿流体中的搅拌功率与表观雷诺数（Ｒｅ＾＊）、弗劳德数（Ｆｒ）以及加料量的变化关系,实验结果表明：Ｍｅｔｚｎｅｒ常数Ｋｓ随加料量的减少而急剧增加;在层流区域,Ｎｐ．Ｒｅ＝Ｋｐ关系仍然成立且非牛顿流体功率曲线与牛顿流体重合。对实验数据进行关联得到了非牛顿流体搅拌功率准数关联式。     

搅拌槽内具滑移特性非牛顿流体的搅拌功率及混合特性研究

在直径为0.48m的搅拌槽内考察了包括CBY、45°斜叶桨及螺带在内的五种搅拌桨对三种不同流变特性的具有滑移现象的非牛顿高黏流体混合效果的影响。首先采用HAAKERS150流变仪对三种流体的流变特性进行测定和表征,比较各种桨型在液位与槽径比H/T为0.28～0.52内的混合效果,得出不同流体中适宜的搅拌桨型及桨型适宜的混合液位范围。结果表明,在具有滑移特性的流体中各种桨型的Metzner常数通常高于经验数值;螺带桨在很宽的表观黏度范围及较宽的雷诺数范围下均表现出较好的混合效果,而CBY及45°斜叶桨型只适用于流体表观黏度较小而雷诺数相对较高的情形。在液位最低时,流体的混合时间和混合能并非最低,各种桨型的最佳操作液位在槽径的0.35～0.43倍内。     

搅拌槽内非牛顿流体的微观混合特性

在直径为0·476m的搅拌槽内,分别选用三窄叶翼型搅拌桨和标准六直叶涡轮搅拌桨,采用羟乙基纤维素(HEC)水溶液非牛顿流体作为工作体系,以改进的硫酸铜沉降反应与氯乙酸乙酯水解反应的平行竞争反应作为研究微观混合的反应工作体系,在质量分数为0·1%~0·5%的HEC水溶液中,排除硫酸铜副反应的影响,利用铜离子质量浓度与可见光吸光度的线性关系,考察了进料时间、搅拌转速、溶液黏度、流体的非牛顿性以及搅拌桨类型等因素对副产物收率(XQ)的影响规律。结果表明,当进料时间超过临界进料时间3500s后,X_Q不再改变;随着搅拌转速的增加,X_Q减小,但其减小的趋势逐渐变缓;在相同转速下,X_Q随着流体黏度的增加而增加,但增加的趋势有所减缓;对于黏性流体不能仅仅采用雷诺数作为放大准则;在相同的能量耗散速率及桨叶区进料的情况下,Damkohler准数较大的标准六直叶涡轮搅拌桨的X_Q较小。     

高粘性非牛顿流体搅拌的研究

本文研究了双螺带搅拌器和另外两种新型搅拌器(收缩桨式、交叉桨式)在非牛顿流体中的搅拌特性,试验比较认为,交叉桨为比较理想的桨叶形式。利用回归组合设计,找出了交叉桨式搅拌器无因次混合时间与几个设备参数之间的关系,通过优化运算得到了最佳参数,并研究了交叉桨在粘弹性流体中的搅拌特性。     

搅拌法测定非牛顿流体流变特性的研究

本文提出一种新的测试方法,即利用搅拌法测定非牛顿流体的流变特性。对该测试技术,理论上进行了阐述和推导,且用实验进行补充和验证,最后给出了完整的测试步骤。该法特别适用于某些“难处理”物料的流变性质测试。测定结果精度完全满足为工程研究提供基础流变数据和工业生产监控应用上的需要。     

宽黏度域轴流桨及在非牛顿流体中功率特性的实验研究

根据某反应的特定工艺过程要求,提出了一种适合宽黏度域的高效轴流式搅拌桨--SP304型轴流式搅拌桨,该桨叶片呈空间扭转状,且具有曲率,可减少流体阻力,提高排出性能.并设计了一套实验装置对这种高效轴流桨在非牛顿流体中的功率特性进行研究,得到了功率常数K_p、Metzner常数k_s和功率特性曲线,为工业化装置的设计提供实验数据.通过观察实验中不同浓度、不同转速下的流体流动细节,可以获得整个流动场的概念,对搅拌桨离低高度、桨间距等参数设计具有重要的指导意义.根据实验结果对此高效轴流搅拌桨成功地进行了工业应用.     

双轴异桨组合搅拌器混合特性及传热性能研究

以聚合反应器中存在的传热,传质问题为研究背景,设计了双螺带－斜叶双驱动变速搅拌器。在实验室基础上,探讨了这一搅拌器的流型、功率消耗、混合特性和传热性能,为该组合浆的开发应用奠定了基础。     

不同组合桨搅拌槽内非牛顿流体的微观混合特性

在直径0.282 m的搅拌槽内,以羟乙基纤维素(HEC)水溶液为工作体系,以磷酸盐?碘化物?碘酸盐平行竞争反应为模型反应,比较了非牛顿流体体系中向心桨、Rushton桨、三斜叶桨的功率准数,考察了加料时间、桨型及双层桨组合对微观混合效果的影响。结果表明,随功率增大,功率准数基本不变,Rushton桨功率准数最大,是向心桨的两倍、斜叶桨的四倍。随加料时间增大,离集指数先减小后不变。在实验考察范围内,单位体积功耗相等的情况下,单层桨微观混合效果的顺序为Rushton桨?向心桨?斜叶桨,双层桨中高剪切的Rushton桨与强循环的斜叶桨组合的微观混合效率最高。     

Power Consumption in the Turbulent Regime for a Coaxial Mixer

The power consumption of a new coaxial mixer composed of an anchor impeller and a pitched‐blade turbine impeller, and a series of rods operated in a contra‐rotating mode has been characterized experimentally in the turbulent regime. It is shown that both the power curve and the turbulent power number vary significantly with the speed ratio between the impellers. Likewise with single impeller mixers, the transition regime starts at a Reynolds number above 100 and the turbulent regime between 10³ and 10⁴ irrespective of the definition of the Reynolds number used.     

旋转盘式混合器混合过程数值模拟

基于旋转盘式混合器的研制实践,采用Polyflow软件在分析其速度和剪切速率分布的基础上,研究了物料粒子的动态混合过程;并从物料停留时间和最大剪切应力分布角度分析了旋转盘式混合器的分布和分散混合性能。结果表明,旋转盘式混合器可提供强大的剪切、置换和压缩作用,随着动盘旋转体转速增加,分散混合性能增强,不利于轴向分布混合。     

双转子连续混炼机混沌型转子混合性能的研究

在提出一种新型混沌型转子结构的基础上,运用Polyflow软件对其混炼过程进行三维非牛顿等温模拟,并借助于粒子示踪法对物料所经历的流场特性进行统计学分析;分析了转子结构和工艺参数对转子混合性能的影响,同时通过共混改性实验,对转子的混合效果进行了评估和表征。结果表明,高混沌型转子的分布混合能力有较大的提高,同时保持着良好的分散混合能力;混沌型转子制备的复合材料力学性能优于经典转子;转子转速的提高可以增强混沌转子的分散及分布混合能力,适当的加料速率是保证取得较好混合效果的关键因素。     

橡胶混炼过程功率曲线新的物理意义

根据密炼机流变理论和橡胶混炼流变理论,赋予混炼过程功率曲线新的物理意义。指出从密炼机混炼过程功率曲线的变化可判断混炼过程是否最佳,打滑是否严重,胶料粘度是偏大还是偏小,加入油料时间是否适时等     

最大叶片式桨流体动力学性能的数值模拟

运用CFD方法研究了最大叶片式桨在层流区域内的流体动力学性能,模拟体系为高粘度牛顿流体和非牛顿流体,主要考察桨叶的功耗特性、Metzner常数、剪切性能和排液性能. 结果表明,功耗计算值与文献实验值基本一致;桨叶的Metzner常数ks=10与流变行为指数n无关;搅拌形成双循环流型,釜中部桨叶所在区剪切速率大、排液量大,产生的漩涡流也大,导致剪切效率低于0.5;随雷诺数增加(Ren=1.4, 5.0, 7.6),全釜平均剪切速率(3.40, 9.91, 15.05 s-1)和全釜平均排液量(0.0014, 0.0033, 0.0052 m3/s)逐渐增加,尤其是桨叶下端两翼区平均剪切速率(4.36, 11.48, 16.35 s-1)和平均排液量(0.0026, 0.0064, 0.0095 m3/s)增加相对较大. 说明Ren增加,搅拌混合作用加强,剪切速率大产生的界面积大,排液量大使高低剪切区内流体快速循环,有利于流体高效混合.     

Dimensional analysis for planetary mixer: Mixing time and Reynolds numbers

Mixing time number is a convenient parameter to characterize mixing performance of stirred tanks. This dimensionless number is now well established for agitated vessels equipped with vertically and centrally mounted impeller for Newtonian as well as for non-Newtonian fluids. To our knowledge, there is more ambiguity concerning its definition for planetary mixers especially when they have dual motion (around two perpendicular axes) to achieve homogenization. In this study, dimensional analysis of mixing time and reliability of the modified Reynolds and mixing time numbers are proposed for such a planetary mixer particularly named as TRIAXE^® system. These two numbers are based on the maximum tip speed of mixer as the characteristic velocity. Modified dimensionless numbers are consistent with the definition of conventional Reynolds and mixing numbers (when only one revolving motion around the vertical axis of the mixing device occurs in the vessel).Mixing time experiments with TRIAXE^® mixer for highly viscous Newtonian fluids showed that the proposed modified Reynolds and mixing time numbers succeeded to obtain a unique mixing curve irrespective of the different speed ratio chosens. This agreement proves that the proposed modified dimensionless numbers can be well adapted for engineering purposes and they can be used to compare the mixing performance of planetary mixers.     

Assessing Blending of Non‐Newtonian Fluids in Static Mixers by Planar Laser‐Induced Fluorescence and Electrical Resistance Tomography

Planar laser‐induced fluorescence (PLIF) and electrical resistance tomography (ERT) were applied simultaneously to monitor the mixing performance of a KM static mixer for the blending of non‐Newtonian fluids of dissimilar rheologies in the laminar regime. The areal distribution method was used to obtain quantitative information from the ERT tomograms and the PLIF images. Comparison of the ERT and PLIF results demonstrates the ability of ERT to detect the mixing performance in cases of poor mixing within the resolution of the measurement, though the accuracy decreases as the condition of perfect mixing is approached. Thus, ERT has the potential to detect poor mixing within the confines of its resolution limit and the required conductivity contrast, providing potential rapid at‐line measurement for industrial practitioners.     

Pressure drop and mixing behaviour of non‐Newtonian fluids in a static mixing unit

Static or motionless mixers have received wide application in chemical and allied industries due to their low cost and high efficiency. The pressure drop and mixing behaviour of such mixers have been widely studied. However, the available information for non‐Newtonian fluids is scanty. The results of pressure drop and mixing studies conducted with a locally made motionless mixer (MALAVIYA mixer) and four non‐Newtonian fluids—aq. CMC, PVA, and PEG solutions are reported in this article. The new mixer causes less pressure drop compared to some of the commercial mixers. Mixing behaviour of the unit is more closer to plug flow and a two‐parameter model correlates the dispersion data.