双层桨搅拌槽内部流场的实验研究

运用计算流体动力学（CFD）方法对双层桨搅拌槽内部流场进行数值模拟。考察了流体在不同桨叶类型、不同桨叶间距对搅拌槽内宏观流动场的影响。研究发现：流体在桨叶间距为150 mm的双层桨内部流场流动效果好。在此间距的基础上得出流体在六圆盘上斜叶桨的搅拌槽内比六圆盘直叶桨搅拌槽内混合效果好。     

刚柔组合搅拌桨增强混合澄清槽内流体宏观不稳定性

流体宏观不稳定性可以反映流体轴向能量和质量的传递行为。为揭示刚柔组合搅拌桨（简称柔性桨）作用下混合澄清槽中油水液-液两相非稳态流动规律,采用频谱分析和小波分析组合法研究混合澄清槽内宏观不稳定性,并进行模拟验证。研究表明,柔性桨在转速低于250 r·min^-1时,流体宏观不稳定频率与转速呈线性关系,而转速超过250 r·min^-1,流体因界面卷吸行为吸入空气,宏观不稳定频率谱图呈现功率谱带,流场结构呈多尺度结构特征,流体宏观不稳定频率消失,液-液混合体系出现明显的乳化现象。与刚性桨相比柔性桨能增强宏观不稳定性,提高流体混合效率,强化能量传递行为。计算模拟发现,柔性桨能明显提高桨叶的抽吸能力,增强流体轴向运动的行为,避免流体过度搅拌,有利于流体澄清。     

双层刚柔组合搅拌桨调控流体宏观不稳定性行为

流体宏观不稳定性是搅拌槽内流体流动存在大尺度低频非稳态准周期现象,可以影响流体的能量﹑质量的传递行为。为揭示在双层组合桨作用下搅拌槽内流体的非稳态流动规律,实验采用频谱分析和流场可视化技术研究双层组合桨搅拌槽内自来水体系的宏观不稳定性,对比分析了双层刚性桨和双层组合桨对流体混合的影响。结果表明:直径为T的搅拌槽内流体宏观不稳定频率与转速呈线性增大趋势,在转速为180 r·min^-1时离底距离 0.25T刚柔组合桨体系的宏观不稳定性频率消失,出现谱带现象,流场呈现多尺度结构特征,而离底距离为0.33T和0.5T的刚柔组合桨体系的宏观不稳定性频率分别为0.5096 Hz和0.3459 Hz。双层组合桨体系分别使流体的混合时间缩短了22.5%和35%左右,减小离底距离,可使流场的规则区减小。双层刚柔组合桨调控流体宏观不稳定性,强化流体的能量传递行为,从而缩短混合时间,提高了流体的混合效率。     

长短叶片复合型刚柔桨强化搅拌槽内流体混沌混合行为

搅拌反应器中混合隔离区的存在是强化流体混合的主要障碍。打破搅拌槽中的对称性流场结构,破坏混合隔离区,可以提高流体混合效率。采用Matlab软件编程计算最大Lyapunov指数(LLE)和多尺度熵(MSE),比较了不同桨叶类型、柔性片长度、柔性片数量和桨叶离底高度以及转速对流体混合的影响。结果表明,长短叶片复合型刚柔桨(RF-LSB)桨叶通过刚柔耦合错位连接,柔性片的形变与随机振动对流体的非稳态扰动,使流场结构不稳定性和不对称性增强,强化了流体混合效果。当柔性片数量为3,搅拌转速为90 r/min时,RF-LSB体系比刚性桨和刚柔桨体系的LLE值分别提高了20.22%和7.98%;三种体系[RF-LSB(柔性片数量为3)、刚性桨和刚柔桨体系]的混合时间(θm)与单位体积功耗(Pv)呈指数型关系,当Pv相同时,RF-LSB(柔性片数量为3)的θm最小,表明RF-LSB(柔性片数量为3)更有利于流体混沌混合。     

双层桨自吸式气-液分散搅拌槽的单相流模拟

运用计算流体动力学(CFD)方法对双层桨自吸式气液分-散搅拌槽进行单相流数值模拟。考察了不同气体分散通道叶片角度、不同下层桨类型、不同桨叶间距对搅拌槽内宏观流动场的影响。研究发现:气体分散通道叶片角度为30°时,流体在上层桨所在平面处的流动没有出现较大的扭曲流动,漩涡较小,能量损耗较少。下层桨为六叶上斜叶桨时,下层桨具有较强的泵送能力,能够将液体有效的泵送到上层桨周围。桨叶间距增大,使槽内轴向循环流动范围增大,但是有可能造成下层桨泵送能力的降低。     

通气式中心龙卷流搅拌槽内气-液两相流的混合特性

运用计算流体动力学（CFD）方法对单通管桨搅拌槽和双通管搅拌槽内部流场进行数值模拟,考察了流体在在单通管和双通管搅拌槽内宏观流动场的效果。研究发现,流体在双通管内部流场流动效果好。在此基础上可以看出,通气式搅拌槽开两个孔比开一个孔效果好．这对搅拌槽的优化设计和_丁业放大效应有一定的实际意义。     

柔性Rushton搅拌桨的功耗与流场特性研究

基于传统的Rushton桨,开发了一种柔性叶片Rushton搅拌桨。采用数值模拟方法研究了柔性桨的功耗及层流和湍流流场特性,并分别采用扭矩测量法和粒子图像测速法进行了实验验证。结果表明,对于实验规模的搅拌容器,当介质黏度与甘油接近时,可用橡胶作为柔性桨叶制作材料。Reynolds数≤100时,柔性桨的功耗大于刚性桨;Reynolds数大于该值后,柔性桨的功耗小于刚性桨。柔性桨叶对被搅拌流体具有自适应特性,流固耦合作用下产生的变形增加了流体的径向流动能力。搅拌低黏度流体时,柔性桨能提升近桨区流体的速度,增加桨叶远端流体的循环流动能力;搅拌高黏度流体时,近桨区和桨叶远端流体的速度均大于刚性桨。就尾涡而言,柔性桨产生的涡量较小,耗能少。     

柔性Rushton搅拌桨的功耗与流场特性研究

基于传统的Rushton桨,开发了一种柔性叶片Rushton搅拌桨。采用数值模拟方法研究了柔性桨的功耗及层流和湍流流场特性,并分别采用扭矩测量法和粒子图像测速法进行了实验验证。结果表明,对于实验规模的搅拌容器,当介质黏度与甘油接近时,可用橡胶作为柔性桨叶制作材料。Reynolds数≤100时,柔性桨的功耗大于刚性桨;Reynolds数大于该值后,柔性桨的功耗小于刚性桨。柔性桨叶对被搅拌流体具有自适应特性,流固耦合作用下产生的变形增加了流体的径向流动能力。搅拌低黏度流体时,柔性桨能提升近桨区流体的速度,增加桨叶远端流体的循环流动能力;搅拌高黏度流体时,近桨区和桨叶远端流体的速度均大于刚性桨。就尾涡而言,柔性桨产生的涡量较小,耗能少。     

几种框式桨搅拌槽内流动特性的比较研究

用粒子成像测速（PIV）技术对传统框式桨、传统框式组合桨和新型框式组合桨的流动特性进行研究,对比了三种框式桨在相同工况下搅拌槽内的速度、流型和湍动能。结果表明：传统框式桨搅拌槽内流体流动以水平环流为主,在框式桨上方和框式桨中间区域流体流动不充分;传统框式组合桨搅拌槽内框式桨上方由于二折叶桨的作用使得框式桨上部流体流速变大,槽内流体上下部的流动得到加强,但在框式桨中心区域依旧存在流动死区;新型框式组合桨搅拌槽内两层桨叶间的连接流得到了加强,框式桨底部和中间区域物质和能量的交换更加充分。在考察的三种框式桨中,新型框式组合桨的混合效果更好。研究结果可为新型框式组合桨应用于化工合成工业中提供参考。     

无挡板涡轮桨搅拌槽内湍流流动的分离涡模拟

采用分离涡模型对无挡板涡轮桨搅拌槽内的湍流流动进行了研究,重点分析了流场结构和速度分布,以检验该模型模拟搅拌槽内流体流动的有效性和正确性. 为了加快收敛,先采用标准k-e模型进行稳态流场计算,并以此结果为初始值进行分离涡模拟. 与现有文献大涡模拟及实验结果对比表明,分离涡模型能捕捉槽内流体的瞬时流动特征,获得的时均速度分布与大涡模拟及实验结果吻合较好,其中对切向速度分布的预测误差不超过7%,对径向速度分布的预测精度则低一些,局部误差接近12%. 分离涡模型适用于无挡板涡轮桨搅拌槽内湍流流动的模拟,能获得与大涡模拟相近的结果,且计算量更小(约为大涡模拟的1/3).     

Coupling simulation of fluid structure interaction in the stirred vessel with a pitched blade turbine

The interaction between fluid and a down-pumping pitched blade turbine fixed with a flexible shaft in the stirred vessel,as a typical fluid structure interaction phenomenon,was simulated by coupling the Computational Fluid Dynamics and Computational Structural Dynamics.Based on the verification of the simulated impeller torque and dimensionless shaft bending moment with experimental result,the dimensionless shaft bending moment and various loads acting on impeller (including lateral force,axial force and bending moment) were discussed in detail.By separating and extracting the fluid and structural components from those loads,the results show that the shaft bending moment mainly results from the lateral force on impeller although the axial force on impeller is much larger.The impeller mass imbalance increases the shaft bending moment and the lateral force on impeller,but has little influence on the axial force and bending moment acting on impeller.The dominant frequencies of impeller forces are macro-frequency,speed frequency and blade passing frequency,and are associated with the impeller mass imbalance.     

Effect of the impeller imbalance on the bending moment acting on a shaft in a stirred vessel

The bending moment acting on an overhung shaft equipped with an unbalanced impeller, as one of the results of the lateral Fluid-Structure Interactions (FSI) in stirred vessels, was measured using a moment sensor, equipped with digital telemetry. The results show that the imbalance of impeller has a considerable influence on the characteristics of bending moment, such as the mean amplitude and the intensity of amplitude fluctuation. Analysis of the amplitude distribution shows that the distribution is well fitted by a Weibull distribution, which tends to flatten and become more symmetrical about the mean as the imbalance increases. Further analysis of the bending moment power spectral density shows that the speed frequency of the bending moment, whose contribution to the bending moment fluctuation increases with the increasing imbalance, is caused by the imbalance of the stirring structure. These results can be applied to the mechanical design process for the shaft and the stirred vessel supporting it, and the manufacturing control of impeller balance quality.     

刚-柔组合搅拌桨强化流体混沌混合

合理设计搅拌反应器的桨叶,强化流体流动与混合行为,是实现流体高效、节能混合的重要手段。柔性体与刚性体组合,可设计出具有多体运动行为的刚-柔组合搅拌桨。结合PIV流场观测和CFD模拟,对比分析了刚性桨和刚-柔组合桨对流场结构及流体混沌混合行为的影响。结果表明,与刚性搅拌桨相比,刚-柔组合桨的柔性端强化能量传递,流体流速衰减速率降低25%,有利于搅拌桨输入能量在流场结构内的有效分配。传统刚性六凹叶和六直叶涡轮桨搅拌反应器内流体形成的流线结构具有明显的周期吸引子,其时均流场的分形维数分别为1.9046和1.9138。刚-柔组合六直叶涡轮桨搅拌反应器内流体流线呈明显的准周期性吸引子性质,其流场分形维数为1.9337,而刚-柔组合六凹叶涡轮桨搅拌反应器内流体流线具有典型的混沌吸引子性质,其流场分形维数为1.9545。刚-柔组合搅拌桨可改变流体流线的吸引子来调控流场的多尺度结构,强化流体混沌混合,实现高效节能操作。     

基于计算流体力学方法的啶虫脒结晶釜搅拌器优化设计

采用计算流体力学(CFD)方法对啶虫脒结晶釜进行了模拟与优化,考察了不同搅拌转速下的速度分布均匀性和晶体体积含量分布均匀性,结果表明,高效轴流型桨SP306对晶体悬浮的效果较好,搅拌转速对晶体体积含量分布均匀性有显著影响,确定了90 r/min为优化后的搅拌转速。经工业应用,验证了优化设计的合理性,产品粒径分布有明显改善。     

Torque and bending moment acting on a flexible shaft agitated by disk turbines in a gas–liquid stirred vessel

The torque and bending moment acting on a flexible overhung shaft in a gas–liquid stirred vessel agitated by a Rushton turbine and three different curved-blade disk turbines(half circular blades disk turbine, half elliptical blades disk turbine, and parabolic blades disk turbine) were experimentally measured by a customized moment sensor. The results show that the amplitude distribution of torque can be fitted by a symmetric bimodal distribution for disk turbines, and generally the distribution is more dispersive as the blade curvature or the gas flow rate increases. The amplitude distribution of shaft bending moment can be fitted by an asymmetric Weibull distribution for disk turbines. The relative shaft bending moment manifests a "rising-falling-rising" trend over the gas flow number, which is a corporate contribution of the unstable gas–liquid flow around the impeller, the gas cavities behind the blades, and the direct impact of gas on the impeller. And the "falling" stage is greater and lasts wider over the gas flow number for Rushton turbine than for the curved-blade disk turbines.     

Effect of gas flow on the bending moment acting on a shaft in a sparged vessel stirred by a Pitched Blade Turbine

The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Pitched Blade Turbine, as one of the results of Fluid–Structure Interactions (FSI) in stirred vessels, was measured using a moment sensor equipped with digital telemetry. The amplitude and Power Spectral Density of the shaft bending moment were analyzed. It shows that the gas flow has a considerable influence on the characteristics of the bending moment, such as the amplitude mean, distribution, Standard Deviation and peak, and the low-frequency and speed frequency contributions to the fluctuation. The relative mean bending moment initially increases with gas rate till the transition from complete dispersion to loading regimes, approaching a peak, then decreases to a valley and again rises gradually, going through the transition from loading to flooding regimes. The “S” trend of the relative mean bending moment over gas flow rate, depending on the flow regime in gas–liquid stirred vessels, results from the competition among the nonuniformity of bubbly flow around the impeller, the formation of gas cavities behind the blades and the gas direct impact on the impeller as gas is introduced.     

Rushton桨气液搅拌槽内气泡流对搅拌轴弯矩的影响（英文）

The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine, as one of the results of fluid and structure interactions in stirred vessels, was measured using a moment sensor equipped with digital telemetry. An analysis of the shaft bending moment amplitude shows that the amplitude distribution of the bending moment, which indicates the elasticity nature of shaft material against bending deformation, fol-lows the Weibull distribution. The trends of amplitude mean, standard deviation and peak deviation character-istics manifest an“S”shape versus gas flow. The“S”trend of the relative mean bending moment over gas flow rate, depending on the flow regime in gas–liquid stirred vessels, resulted from the competition among the non-uniformity of bubbly flow around the impeller, the formation of gas cavities behind the blades, and the gas direct impact on the impel er when gas is introduced. A further analysis of the bending moment power spectral density shows that the rather low frequency and speed frequency are evident. The low-frequency contribution to bend-ing moment fluctuation peaks in the complete dispersion regime.     

Numerical and experimental analyses of a stirred vessel for a large volumetric flow rate of sparged air

Computational fluid dynamics (CFD) and experimental analyses of some of the basic characteristics of air sparging in a tall stirred vessel equipped with a three-stage impeller are presented. The impeller was assembled from a radial ABT impeller as the lower, a turbine 6PBT45 as the middle and an axial Scaba-type 3SHP1 impeller as the upper. All the impellers were of the same diameter, i.e., 225 mm, while the vessel diameter was 450 mm. The impeller's rotational speed was 178 r·min^-1. The aeration regime was established with an air volumetric flow rate of 28.3 m³·h^-1. To the best of our knowledge, this study is the first to consider the very high gassing rate by means of CFD in a tank stirred by three-stage axial/radial impellers. The numerical simulation was performed using the ANSYS Fluent (R17.2, 2016) code for solving the governing equations of fluid dynamics in single- and multi-phase systems. While discussing the bubble size distribution, a discrete population balance model (PBM) was used. Adopting CFD, the stirring power and the total void fraction (the total gas holdup) were calculated. The results were in good agreement with the measured values using a laboratory experimental device.     

流体中气泡微细化与分散过程的数值模拟

采用CFD商用软件模拟了搅拌加喷吹情况下溶池中流场和相的分布.对比分析了水模型内单相流和两相流时液面和轴向迹线图、矢量图和相分布图,重点考察了中心搅拌和偏向搅拌对漩涡和相分布的影响规律.模拟结果表明,中心搅拌模式下在搅拌桨轴附近形成很大的漩涡,偏心时虽然也有漩涡形成,但偏离轴心.两相流偏心搅拌模式下由于漩涡较小且偏离轴心,有利于气体的分散;偏心搅拌与中心搅拌相比可以抑制漩涡在几何中心的形成,有利于气体的分散和气泡的细化,同时偏心搅拌也可以有效地抑制水模底部的死区.研究结果对喷气机械搅拌装置的设计具有参考价值.