搅拌生物反应器的循环时间分布和混合结构模型

利用磁粒子流动跟踪法对搅拌生物反应器的循环时间分布进行测定,并将Rushton径向流桨和两种新型轴向流桨在不同介质粘度和转速下的循环时间分布进行比较和性能评价。建立了单桨搅拌生物反应器的混合结构模型,对循环时间分布数据进行拟合,求得模型参数,进而讨论了不同实验条件下模型参数的变化。结果表明,对于非牛顿、高粘度发酵过程,轴向流桨比Rushton桨具有更好的混合特性。     

改进型框式组合桨搅拌釜内流场特性

对5m³树脂反应釜及釜内改进型框式-二斜叶双层组合桨等比例缩小建立模型,基于计算流体力学（CFD）中的多重参考系法对该双层组合桨搅拌釜流场进行了模拟研究,并利用粒子图像测速（PIV）实验对模拟结果进行了验证。分析了桨叶离底间距、桨间距及组合桨安装角度的变化对流场产生的影响。随着离底间距的增大,搅拌釜下层框式桨横梁处产生往槽底的轴向流强度会逐渐减弱,不利于底部物料的混合;桨间距的增加导致两桨间对流减弱,不利于两桨间流体的混合,当桨间距与釜内径的比值为0.77时,搅拌釜内的整体流动情况较好。对上下层桨叶安装角度分别为0°、45°和90°这3种工况下的釜内流场特性研究表明,安装角度为90°时,斜叶桨产生的轴向流强度最大,此时搅拌釜内流体的混合效果最好。研究结果为改进型框式桨与二斜叶桨双层组合桨应用于树脂聚合反应实际工程提供参考。     

旋转泡沫填料反应器的研究进展

旋转泡沫填料反应器是一种新型多相搅拌釜式反应器,其将传统的搅拌桨替换成圆环型泡沫填料,可有效强化反应器内多相间传质混合过程,且多孔填料可作为催化剂载体,能减小多相催化反应中固体催化剂的使用量,具有替换传统多相搅拌釜式反应器和浆态反应器的潜力,将有较好的应用前景。本文详细阐述了旋转泡沫填料反应器的结构和反应器内多相流动形式,着重介绍了反应器内多相流动特性的研究进展及反应器内传质性能的研究现状,并与传统的多相反应器传质性能进行比较;从应用方面分析了反应器用于葡萄糖催化氧化、苯乙烯催化加氢等多相过程的强化方式及优势,通过对比得出旋转泡沫填料反应器能有效降低化工过程中物耗、提高物料的利用率;介绍了与旋转泡沫填料反应器类似的其他多孔式搅拌桨反应器的研究进展,分析了这类反应器的优势,并对其性能进行对比;最后,对旋转泡沫填料反应器研究的不足及未来的发展进行了阐述和展望。     

无挡板悬浮聚合搅拌釜的粘釜规律

在φ300mm的有机玻璃釜中,用聚苯乙烯颗粒(PS)和粘胶建立了釜内流动条件对粘釜影响的冷模实验方法。研究了无挡板条件下搅拌釜内粘垢的产生及其分布规律,发现在相同搅拌功率下,各种搅拌桨叶对粘釜量的影响从低到高依次为双叶推进式桨、双叶45°斜桨、三叶后掠式桨、双叶60°斜桨、双叶平桨及六叶透平式桨,纵向分布随流型有所不同。并讨论了搅拌桨安装方式及搅拌转速对粘釜规律的影响。     

基于介尺度PBM模型的生物反应器放大模拟及实验研究

对于通气搅拌式工业生物反应器的放大设计而言,精确预测气泡尺寸和体积传质系数非常重要,因此需要建立合适的气泡聚并和破碎模型,以保证反应器的高效操作。以5 L通气搅拌式生物反应器为对象,以气泡尺寸和体积传质系数的实验数据为基准,模拟并考察了两种聚并模型和四种破碎模型对生物反应器内流体流动行为以及传质能力的影响。结果表明,基于介尺度理论的修正聚并模型与考虑黏流剪切的破碎模型组合,所得模拟结果与实验数据吻合最好,这为大型生物反应器的桨型优化提供了模型基础。因为工业化生物发酵通常是在大型生物反应器中进行,搅拌桨型对生物反应器效能至关重要,故本研究在选定最优气泡聚并破碎模型的基础上,通过叶轮末端剪切力相等的放大原则将5 L通气搅拌式工业生物反应器放大到400 m³,同时考察了六斜叶圆盘搅拌桨、非对称式抛物线搅拌桨、布鲁马金式搅拌桨以及六直叶圆盘搅拌桨等桨型组合对气泡破碎能力和气体分散效果的影响,并通过综合对比气含率、体积传质系数等参数,得到400 m³通气搅拌式生物反应器的最优桨型组合。     

大型侧进式搅拌釜内湍流流场的数值模拟

采用计算流体力学(CFD)技术对直径和高度均为13 m的大型侧进式搅拌釜内均相宏观流场进行数值计算。结果表明,将计算域划分为大约90万网格时,计算得到的搅拌功率曲线与实验数据吻合较好;考察不同操作转速、搅拌桨安装角度及个数对釜内低速死区分布的影响,发现增大搅拌转速很难有效地消除水平面上的死区;搅拌桨垂直向下5.71°或水平偏转11°安装能明显改善流体运动。三桨和四桨搅拌体系对釜上部流场的优化要好于两桨体系;但在相同转速下,双桨、三桨和四桨搅拌釜的搅拌功耗分别是单桨搅拌釜的1.2倍、2.3倍和3.4倍。综合考虑,三桨体系搅拌效率较高。最后采用组分模型计算得到不同转速下三桨釜的混合时间。     

工业聚合反应装置：Ⅳ.乳液聚合反应器（下）

讨论了釜式乳液聚合反应器搅拌桨的选择原则及其搅拌特性和乳液聚合反应器的放大准则，聚合过程的控制及其优化。     

疏水Rushton搅拌桨的减阻性能

为了减小搅拌阻力与功耗,本研究提出了疏水叶片搅拌桨的设想。首先采用数值模拟的方法,对非疏水Rushton桨搅拌容器内的流场进行了模拟,通过与文献中实验结果的对比,验证了数值模型和模拟方法的可靠性。随后研究了湍流状态下疏水Rushton搅拌桨的流体动力学性能,分析了不同疏水状态下的流场结构、剪应力和压力分布以及减阻效果和搅拌功耗,并与非疏水桨进行了对比。结果表明,疏水处理后Rushton桨搅拌容器内的流场没有明显变化,但流体的轴向泵送能力有所增强,高速度区域略有扩大,超疏水时效果更明显。疏水处理可降低Rushton桨的剪应力和桨叶前后表面间的压差,具有减阻效果,超疏水时减阻幅度高达39.56%。另外,疏水Rushton桨的搅拌功耗有所降低,与非疏水桨相比,超疏水桨的功率准数降低了8.53%,具有显著的节能效应。     

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。     

轴流式翼型-透平组合桨在搅拌釜内的流动

<正>搅拌反应器是化工、医药、食品工业中广泛应用的基础设备之一,当搅拌釜内液深与搅拌釜直径相比较大时(通常比值大于1),往往采用双层或多层桨,以保证顶部到底部的循环流动。 透平桨产生的是径向流,形成以桨叶为中心线的上、下2个循环区,桨叶附近剪切速率高,气体分散能力强。翼型桨产生的流型是轴向流,形成全釜循环,混合均匀,剪切温和。为充分利用两者优势,加强全釜混合,剪切适度,特别是在粘稠物系中,可采用组合桨。目前尚未看到对翼型-透平组合桨流动状况的研究,而对于非牛顿流体中的组合桨流动状况则了解     

Application of KHX Impeller in a Low-shear Stirred Bioreactor☆

In our previous work, a low-shear stirred bioreactor was explored. With a pitched blade turbine impeller downflow (PBTD) used, the shear stress generated is high compared with that in some low shear ax...     

固-液搅拌槽内桨型对颗粒悬浮特性影响的实验和模拟研究

以水为液相，玻璃珠为固相，在固-液搅拌槽内比较了传统径向流Rushton桨、轴向流下推式45°六斜叶桨以及新型半折叶搅拌桨的功耗、泵送能力和对固体颗粒的悬浮效果。并应用CFD （Computational fluid dynamics）方法研究了不同搅拌桨操作下颗粒的轴向速度分布。结果表明：在相同转速下，Rushton桨的功耗最大，新型半折叶桨与下推式45°六斜叶桨的功耗接近；新型半折叶桨的流量准数最大，泵送能力最强；在固-液体系中，新型半折叶桨与下推式45°六斜叶桨的流型类似，但3种桨中新型半折叶桨对固体颗粒的悬浮效果最好。     

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.     

Impact of impeller type on methyl methacrylate emulsion polymerization in a batch reactor

The emulsion polymerization of methyl methacrylate (MMA) was carried out in a lab‐scale reactor, which was equipped with a top‐entry agitator, four wall baffles, a U‐shaped cooling coil, and a temperature controller. Potassium per sulfate and sodium dodecyl sulfate as were used as the initiator and the surfactant, respectively. The experimental investigation demonstrated the impact of the impeller type (45° six pitched‐blade turbine and Rushton impeller), number of impellers (single and double impellers), and impeller speed (100–350 rpm) on the monomer conversion, polymer particles size, molecular weight, and glass transition temperature. The results revealed that the effect of the impeller speed on the characteristics of the polymer attained using the pitched‐blade turbine was more prominent than that for the Rushton turbine. It was also found that the impact of the impeller speed on the polymer characteristics was much more pronounced for the double pitched‐blade turbines rather than for the double Rushton turbines. However, more uniform size distribution was achieved with the Rushton turbine. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40496.     

The Use of Positron Emission Particle Tracking in the Study of Multiphase Stirred Tank Reactor Hydrodynamics

This paper describes the use of positron emission particle Tracking (PEPT) in the analysis of local particle and fluid velocities in solid‐liquid stirred tank reactors agitated with a Rushton turbine and an upward‐pumping pitched blade turbine. PEPT captures the full three‐dimensional characteristics of hydrodynamics and mixing in stirred vessels, allowing the analysis of the two‐phase flow fields. Furthermore, by comparing the liquid and particle velocities, the spatial and temporal variation of the relative particle‐liquid velocity can be estimated. Such information reveals considerable heterogeneity in the vessel and facilitates the evaluation of impeller design, particularly with the aim of minimizing mass transfer limitations.     

Gas recirculation rate and its influences on mass transfer in multiple impeller systems with various impeller combinations

Both the numerical and experimental approaches were used to study the effects of the gas recirculation and non‐uniform gas loading on the mass transfer rate for each impeller in a multiple impeller system. By combining the calculated gas velocity and local gas holdup, the gas recirculation rate around each impeller was estimated. The local mass transfer coefficients for systems equipped with various combinations of the Rushton turbine impeller (R) and pitched blade impeller (P) were determined by using the dynamic gassing out method. It is found that the Rushton turbine impeller has to be served as the lowest impeller in order to have a better gas dispersion and to give a higher overall K_La for a multiple impeller gas‐liquid contactor. The upper pitched blade impeller always enforces the circulating flow around the Rushton turbine impeller just beneath it and gives a higher overall average mass transfer rate. However, the system equipped with only the pitched blade impellers results in a much lower mass transfer rate than the other systems owing to the poor gas dispersion performance of the pitched blade impeller.     

Numerical Investigation of the Effect of Impeller Design Parameters on the Performance of a Multiphase Baffle‐Stirred Reactor

The turbulent gas‐liquid flow field in an industrial 100‐m³ stirred tank was calculated by using computational fluid dynamics based on the finite‐volume method. Turbulent effects were modeled with the shear stress transport model, and gas‐liquid bubbly flow was modeled with the Eulerian‐Eulerian approach using the Grace correlation for the drag force interphase momentum transfer. The relative motion between the rotating impeller and the stationary baffled tank was considered by using a multiple frames of reference algorithm. The effects of Rushton and pitched‐blade impeller design parameters such as blade geometry, location, and pumping direction on the mixing performance were investigated. It was found that a combination of Rushton turbines with up‐pumping pitched‐blade turbines provides the best mixing performance in terms of gas holdup and interfacial area density. The approach outlined in this work is useful for performance optimization of biotechnology reactors, as typically found in fermentation processes.     

On the Manifestation and nature of macroinstabilities in stirred vessels

The flow variations or macroinstabilities (MIs) occurring in a vessel stirred by a pitched blade turbine (PBT) are studied through particle image velocimetry (PIV) experiments. Proper orthogonal decomposition and fast Fourier transform techniques are applied to the PIV velocity data at one vertical and nine horizontal planes below the impeller, to identify and characterize the flow structures present in the vessel. It is shown that the PBT MI is manifested as a precessional movement around the impeller axis and an oscillation in the direction of the axial mean stream around the shaft axis. The identified flow structures are similar to those previously observed in vessels stirred by Rushton impellers and are characterized by two dominant frequencies, equal to one‐tenth and one‐fifth of the impeller rotational speed. The nature and extent of these structures and their interaction with the trailing vortices emanating from the turbine blades are discussed. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Investigation of impeller modification and eccentricity for non-Newtonian fluid mixing in stirred vessels

A shear thinning fluid (1% carboxymethyl cellulose) was used to investigate mixing under laminar flow conditions in an unbaffled vessel. The effects of impeller modification in addition to eccentricity were studied. Quantitative measurements such as percentage of uncovered area and coefficient of variance (CoV) of a tracer solution distributed inside the vessel were obtained using planar laser-induced fluorescence (PLIF) method. Increased eccentricity was found to be more effective than increasing rpm alone in reducing isolated mixing regions size (determined by the percentage of uncovered area). The dual-flow pitched blade turbine (DF-PBT), which was the modified version of a standard pitched blade turbine (PBT), was designed to provide both upward and downward flow at the same time to induce more chaotic flow. Though numerical analysis showed this type of flow generated, DF-PBT did not return lower values for the percentage of uncovered area and CoV than PBT did. Power consumption data were also compared between the two impeller types and eccentric locations. Further analyses focusing on the interactions between the impeller blades and fluid rheology is needed to improve laminar mixing in stirred vessels by impeller modification.     

多层桨搅拌槽内的微观混合特性

在直径0.476 m的多层桨搅拌槽内,采用平行竞争反应工作体系,就不同的多层桨型组合、进料时间、搅拌转速及进料位置对产物分布的影响规律进行了系统的实验研究,并采用涡旋卷吸模型就加料位置等操作条件对产物分布的影响进行了模拟计算,模拟值与实验值吻合. 结果表明,对于多层桨搅拌体系,在液面处加料时产物分布主要由上层桨的桨型决定,底层桨的排出流区加料时主要由底层桨的桨型及功率决定. 卷吸模型能够较好地描述搅拌槽内的微观混合过程.