假塑性流体搅拌槽内停留时间分布

在直径φ500 mm和高350 mm的无挡板半球底有机玻璃槽中,采用45°斜叶桨研究了流量、搅拌功率、全槽平均表观牯度和物料流变特性对停留时间分布(RTD)的影响.结果表明,对于假塑性流体(流变指数为0.654)和牛顿流体,流量对RTD的影响两者差别不大,搅拌功率的增加更容易改变假塑性流体的RTD,使其更趋于全混流;对于牛顿流体,当搅拌功率大到一定程度后,再增加搅拌功率收效不大.假塑性流体的相对全混釜数随着全槽平均表观粘度的增加而增加,在全槽平均表观粘度相同时,假塑性流体的相对全混釜效大于牛顿流体,随着流体假塑性的增强,假塑性流体与牛顿流体相对全混釜数的差值显著增大.     

六弯叶搅拌槽内假塑性流体流场及洞穴变化的数值模拟

利用计算流体力学的方法,对六弯叶搅拌器在黄原胶水溶液(一种具有屈服应力的假塑性流体)中的流场及洞穴变化进行研究,得到了搅拌器的功率准数、流动准数、泵送效率以及洞穴大小随雷诺数的变化情况.结果表明,层流状态下,功率准数与雷诺数成反比,流动准数和泵送效率随雷诺数增加而增大,随流体粘度增加而降低,采用Herschel-Bulkley流变模型模拟的洞穴形状为圆柱形.DcT时,洞穴大小符合Elson模型的理论计算结果,在双对数坐标图中,Dc/D与P0Rey接近线性关系,拟合后的直线斜率为0.35.     

错位六弯叶搅拌槽内假塑性流体的混合特性

在直径为0.21 m的搅拌槽内,使用FLUENT?软件对错位六弯叶桨的流动场及混合性能进行了数值模拟.工作介质分别选用牛顿流体(水)和假塑性流体1.0%(wt)黄原胶水溶液,计算采用标准κ-ε湍流模型,并将牛顿流体的速度场分布与粒子图像测速仪(PIV)实验结果进行了比较.通过与标准六弯叶桨进行对比分析,阐述了错位桨用于假塑性流体搅拌时在混合速率和混合效率方面的特性.结果表明:速度矢量的计算值与 PIV 实验数据吻合较好,湍流模型的计算结果可靠;混合过程与流场结构密切相关,监测点位置对浓度变化有较大影响.错位六弯叶桨的混合时间数明显小于标准六弯叶桨,混合速率更高,同时错位六弯叶桨的混合效率大大高于标准六弯叶桨,单位体积混合能只有标准六弯叶桨的52%,具有节能功效,体现出错位桨的优越性.     

高粘度假塑性流体搅拌功率的研究

本文研究了适用于高粘度假塑性流体的螺带螺旋组合式新型搅拌器的搅拌功率，并得出了搅拌功率并联式。     

假塑性流体的雾化研究

用于高粘度物料的二汉式喷嘴，在气体通道内放置螺旋槽后，使进入喷嘴的气流在螺旋槽的引导下成为有一定旋转角度的高速气流。考察了该气流对物料雾化的效果，并比较了喷嘴的不同结构形式对雾化特性的影响。     

双层桨搅拌假塑性流体混合特性的数值模拟

在直径为0.21 m的搅拌槽内,采用计算流体力学的方法,工作介质为质量分数1.0%的假塑性流体和1.5%的黄原胶水溶液,分别对错位六弯叶桨、六弯叶桨与45°三斜叶桨组成的双层桨混合性能进行了数值模拟,并做了对比分析,考察了层间距对搅拌流场的影响,探讨了不同形式的组合桨对混合特性的影响,确定了不同搅拌转速下较为适宜的层间距,并将错位六弯叶组合桨形式应用于FCC催化剂成胶搅拌过程。结果表明:在层流状态下,6PBT组合桨层间距为时可形成层间连接流,在过渡流区域时,层间距保持在左右比较适宜;6PBT组合桨在混合速率和混合效率方面都有一定优势。根据中试实验结果,催化剂颗粒耐磨损指数由2.6提高到了1.9,产品质量得到进一步提高,且节能在15%左右,因此是一种值得推广的双层组合搅拌器形式。     

假塑性流体在双螺带桨搅拌釜内停留时间分布

采用电导率法研究了羧甲基纤维素水溶液假塑性流体在双螺带搅拌釜内的停留时间分布(RTD)情况,考察了物料黏度、流量、搅拌转速和转向对停留时间分布的影响.发现假塑性流体在釜内的停留时间分布类似于全混釜,但有一定的拖尾现象.物料黏度对平均停留时间和当量全混釜数影响不大;随着流量增大,平均停留时间减小,而当量全混釜数基本不变;...     

错位六弯叶桨在假塑性流体中的混沌搅拌特性

基于混沌混合理论,提出了一种错位叶片的结构形式,用来消除层流流场的混合隔离区.利用CFD的方法,对六弯叶涡轮(6BT)和错位六弯叶涡轮(6SBT)2种搅拌器在黄原胶水溶液中的流场变化进行研究,分析比较了2种搅拌器的流场结构、速度分布以及功率消耗的不同.结果表明,模拟计算得到的功率值与实验测量值吻合较好,6SBT桨在层流...     

假塑性流体雾化研究：Ⅰ.雾化特性的研究

本文采用二流式气动喷嘴，通过激光衍射粒径分布测量系统对假塑性流体料液的雾化特性进行了试验研究，得到了物料特性（主要指粘度）和操作参数（主要指气液质量比和空气速度）以及喷嘴液气出口面积比对雾滴平均直径和尺寸分布参数的影响，并进行回归，得到预测雾滴平均直径及尺寸分布参数的关联式。     

Determination method of the cavern boundary viscosity in a stirred tank with pseudoplastic fluid

It is essential to predict the cavern boundary accurately for investigating the cavern characteristics and achieving efficient mixing of the pseudoplastic fluids. The distribution characteristics of apparent viscosity of xanthan gum solutions at different mass concentrations stirred by the impeller of perturbed six-bent-bladed turbine (6PBT impeller) were numerically investigated through the computational fluid dynamics (CFD) simulation based on laminar flow model. The determination method of the cavern boundary viscosity was presented, and the predicted results were compared with those of traditional velocity method. Results showed that the data of the power consumption predicted using CFD simulation agreed well with those measured by torque experiment, which validated the laminar flow model. The η_a − γ curve changes from nearly horizontal straight line to the power function curve along the direction of center axis toward tank wall. As a result, the location of the transitional point can be determined as the cavern boundary, and the corresponding viscosity is the cavern boundary viscosity. The ratio of the cavern boundary viscosity and the fluid yield viscosity ( η_a/η_y ) always remains approximately constant, that is, at different speeds. Compared with the traditional velocity method, the boundary viscosity method can maintain its high accuracy for exhibiting the cavern boundary, and the predicted cavern size and development are always in good agreement with the CFD results free from the speed and the impeller type. So this work can provide a new way for accurately characterizing the cavern boundary.     

Formation of heart-shaped cavern model in stirring pseudoplastic fluid with the impeller of perturbed six-bend-blade turbine

The cavern characteristics of xanthan gum solution stirred with the impeller of perturbed six-bend-blade turbine (6PBT impeller) were studied based on CFD laminar flow model. The heart-shaped cavern model was presented for predicting the cavern development accurately, and the predicted results were made a contrastive analysis with that of other existing cavern models. Results showed that the calculated values agreed well with the data measured by PIV, which validated the laminar flow model. The correction coefficient k = 0.64 is more suitable to revise the characteristic parameter a in the equation of the heart-shaped cavern model. As a result, the heart-shaped model always keeps high prediction accuracy at the cavern boundary. The cavern boundary curves predicted by the heart-shaped model are in good agreement with the results of CFD simulation, and the cavern development along the axial height can be also realistically exhibited. The heart-shaped cavern model will contribute to increase the prediction accuracy of cavern development.     

错位六弯叶桨搅拌假塑性流体流场宏观不稳定性数值模拟

采用分离涡模型,对错位六弯叶（6PBT）搅拌槽内流场结构和宏观不稳定性（MI）进行了数值模拟。工作介质分别选用去离子水和不同质量分数的黄原胶水溶液,并将水的速度场分布与PIV实验结果进行了比较。通过采集监测点的速度时间序列,结合MATLAB软件编程,计算得到流场宏观不稳定频率的变化。结果表明：流场结构和速度矢量的计算值与PIV实验数据吻合较好,分离涡模型的计算结果可靠;提高转速,槽内假塑性流体MI频率峰值增大,脉动强度提高,当转速达到225 r·min^-1时,MI频率特征消失,频谱图呈现谱带现象,意味着流场进入混沌;流体的流变性对MI没有影响,MI现象是流体流动的共有特征。     

Modeling of cavern formation in yield stress fluids in stirred tanks

Prediction of cavern formation in yield stress fluids in stirred tanks is of great importance for optimization. A new torus model is developed and then validated by experimental data and computational fluid dynamics simulation. Unlike existing mathematical models, the new torus model assumes that the circular center of the torus should not be outside the impeller swept region as the Reynolds number (Re) increases. Hence the cavern boundary is shaped like an apple torus rather than a horn torus. The new model also considers the cavern‐vessel interactions. At relatively high Re, the new model predicts cavern shape and size better than other models. It correctly captures the cavern outline at various Re, which verified the assumption about torus center. The new model is then used to identify the influence of rheological parameters on cavern formation, and further extended to the cavern prediction of the dual‐impeller system. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3057–3070, 2014     

基于流固耦合的错位桨搅拌假塑性流体动力学特性

基于ANSYS Workbench分析平台,采用双向流固耦合计算方法,对错位六弯叶搅拌器）6PBT）和六弯叶搅拌器）6BT）的动力学特征进行了对比分析,根据桨叶与流体之间相互耦合运动特性,探讨了宏观流场的结构和搅拌功耗特性,分析了桨叶的变形和等效应力分布,并对6PBT桨在静态和预应力状态下的模态进行了对比研究。结果表明：同6BT桨相比,6PBT桨叶端部变形量增加了8%,端部应力提高了61%,而根部应力降低了6.7%,应力沿径向呈均匀化分布,这表明错位桨对流体的作用力更大,能够更快地传递能量,同时桨叶强度也得到相应提高;6PBT桨的静模态与预应力模态振型分布一致,在施加预应力后模态频率无明显改变,说明桨叶流场的流固耦合作用和预应力对桨叶模态的影响不大;随转速的增大,6PBT 桨的节能效果显现,体现出错位桨的优势。     

流体流变性对错位六弯叶桨流场特性的影响

利用计算流体力学(CFD)的方法,以高黏牛顿流体和假塑性非牛顿流体为研究对象,对错位六弯叶桨在层流域的搅拌流场特性进行了研究。结果表明:数值计算得到的功率值与实验测量值吻合较好,搅拌雷诺数对假塑性流体搅拌流场的量纲一速度和切应变速率影响较大,因此提高转速对改变流场的速度及切应变速率分布是一个有效的办法;而流体的流变性只对假塑性流体的量纲一速度有明显影响,对切应变速率影响较小,当流变指数n<0.3时与n基本无关。当流动由层流向过渡流转变时,搅拌桨的流量准数及泵送效率有显著提高;假塑性流体的流变指数降低时,其泵送效率显著下降。研究进一步认识了错位桨在不同流体中的搅拌流场特点,为高黏假塑性流体搅拌桨的设计、应用以及开发新型搅拌桨提供了参考。     

聚酰胺酸溶液的流变性能研究

采用锥板粘度计研究了聚酰胺酸溶液的流变性能及其粘度的影响因素。结果表明:聚酰胺酸溶液属于非牛顿假塑性流体,还具有负触变性流体的特征。聚酰胺酸溶液的粘度随剪切速率的增加而减小,随浓度的增加而增大,随温度的升高而降低,随存放时间的延长而下降;质量分数为15％的聚酰胺酸溶液的粘流活化能为20．83 kJ／mol。