Flow,suspension and mixing dynamics in DASGIP bioreactors,Part 2

This work aims to characterize the mixing and suspension dynamics occurring within two commercially available DASGIP bioreactor configurations, equipped with a two-blade paddle impeller with large impeller to tank diameter ratio, D/T = 0.97. Both continuous and intermittent agitation modes were employed to determine the impact that agitation strategy has upon mass transfer and microcarrier settling/suspension. This paper builds upon the flow dynamics data presented in Part 1 for a flat bottom DASGIP bioreactor and shows how intermittent agitation can break-up regions of slow mixing observed during continuous agitation, therefore substantially increasing the mixing efficiency of the system. Similarly, it was found that microcarrier characteristics might significantly affect the level of suspension when the impeller is in dwell status when intermittent agitation modes are used.     

Flow,suspension, and mixing dynamics in DASGIP bioreactors: Part 1

The bioreactor flow environment has a significant impact on process performance, especially in stem cell cultures. The work of Correia et al found intermittent agitation modes to improve induced pluripotent stem cell (iPSC)-cardiomyocyte differentiation yields; however, to date, the impact within the flow has not been fully characterized. This work aims to characterize the flow dynamics occurring within a commercially available DASGIP bioreactor, equipped with a two-blade paddle impeller, operating under different agitation modes and for two bottom geometries. The paddle impeller configuration generated an axial flow profile due to a large impeller D/T and blade confinement with the bioreactor wall. The application of intermittent agitation was shown to induce two transient spikes in flow velocity and shear stress, the amplification of which increased with dwell duration. Marginally increasing the dwell duration was shown previously to increase differentiation yields, therefore it can be stipulated that introduction of these spikes was favorable toward cardiogenic differentiation.     

Wood Pulp as Model Fluid to Mimic the Oxygen Mass Transfer in Aspergillus Niger Fermentation

To characterize the oxygen mass transfer in a fermentation system and to study the efficiency of mixing devices, model fluids are often used so that experimental conditions can be better controlled. In this study, wood pulp suspensions were used in an attempt to mimic the rheological properties of fermentation broths of Aspergillus niger. Two different types of bioreactor were used: a reciprocating plate bioreactor and a stirred (Rushton) bioreactor. The oxygen mass transfer coefficient (K_La) was measured for various mixing intensities, airflow rates and wood pulp concentrations, and a correlation of K_La as a function of the power input per unit volume and the superficial gas velocity was derived for each bioreactor and each pulp concentration. K_La was found to increase with agitation and air flow rate, and was adversely affected by an increase in pulp concentration in the case of the reciprocating plate bioreactor.     

低高径比气升式环流反应器数值模拟分析

利用商用计算流体力学软件Fluent,利用Euler-Euler双流体模型,重点针对好氧反应的特点,对一种具有低高径比(H/D=1.67)的环流气升式反应器内的气液两相流动及混合性能进行研究,描述出反应器内气含率和环流液速等参数的详细分布,分析模拟结果,气液速度分布和气含率分布等与实际情况基本吻合,从而证实了计算结果的有效性,为工业实际应用提供一定参考。     

Microcarrier cell culture and its application to the large-scale production of human fibroblast interferon

Animal cells are important in producing several products, but anchorage-dependency of most cell strains is one of the difficulties to get over. Microcarrier was utilized in this study in order to increase the surface area for cell-anchorage and also to improve other characteristics of the cell culture system. First the critical parameters affecting the initial attachment were determined. The best plating efficiency was found at pH = 7.4 and 5% FCS concentration. Use of the intermittent stirring during the initial phase of cell culture gave better cell plating than the continuous stirring. Next the human fibroblast interferon was successfully produced from cells cultured on microcarrier and several advantages of using microcarrier were identified. Usually 10,000 units/ml of interferon was produced from microcarrier culture as compared to 6,000 units/ml in monolayer culture. FCS concentration in cell growth stage affected the yield of interferon and gave optimum results at 5%. Antibiotics did not influence the production of interferon significantly. The highest sensitivity in interferon assay was obtained with Hep 2 cells as the target cells and more than 3 x 10⁵ cells/ml were needed for good result. Microcarrier culture fixed onto confluent monolayer showed results as good as suspension microcarrier culture.     

EXPERIMENTAL STUDY ON MIXING: POWER CONSUMPTION AND DEGREE OF SUSPENSION

An experimental study on mixing, degree of suspension and power consumption in solid-liquid suspensions was done. A system similar to those found in anaerobic fermentation processes of animal manures was used, and an existing mixing equipment was adapted for the study. Power consumption and degree of suspension for both mechanical mixing and mixing by gas was determined. The influence of variables such as geometry, solids concentration, stirrer velocity, and gas velocity was studied, discussed, and compared to data from the literature. Best results were obtained for gas mixing, the power consumption being about one fourth of that required by mechanical agitation. Finally, extended correlations relating Power and Reynolds numbers for mechanical mixing and mixing by gas are proposed.     

HE HYDROLOGY OF OVERLAND FLOW IN WETLANDS

An experimental study on mixing, degree of suspension and power consumption in solid-liquid suspensions was done. A system similar to those found in anaerobic fermentation processes of animal manures was used, and an existing mixing equipment was adapted for the study. Power consumption and degree of suspension for both mechanical mixing and mixing by gas was determined. The influence of variables such as geometry, solids concentration, stirrer velocity, and gas velocity was studied, discussed, and compared to data from the literature. Best results were obtained for gas mixing, the power consumption being about one fourth of that required by mechanical agitation. Finally, extended correlations relating Power and Reynolds numbers for mechanical mixing and mixing by gas are proposed.     

Novel bioreactor design for the culture of suspended mammalian cells. Part I: Mixing characterization

Mammalian cells are extremely sensitive to mechanical stress. Ideally, a bioreactor design for mammalian cell culture should assure adequate mixing at low mechanical stress. This paper focuses on the mixing characterization of a novel stirred tank bioreactor configuration, proposed for the culture of mammalian cells, based on the principle of displacing the agitation shaft to an eccentric position and replacing the impellers normally used for mammalian cell culture with a disc impeller with no blades. Experiments in a 1.0 L prototype are conducted to study flow patterns using UV light visualization techniques. Three different impeller shaft positions are tested E=0.0,0.21, and 0.42. For the purposes of this work, eccentricity (E) is defined as the distance between the shaft and the vertical centerline of the tank/tank radius. The mixing performance of two different impeller disc diameters (3.0 and 5.0 cm) are compared. Experimental results show that adequate mixing conditions are achieved at very low Re numbers for some of the eccentric cases considered. Computations are used to illustrate mixing improvement caused by eccentricity, and to validate the existence of globally chaotic conditions for the eccentric cases tested experimentally.     

一种新型混合装置的开发与研究

混合与许多化工过程密切相关,为了克服传统的搅拌混合装置或结晶器的缺点,运用薄膜振动混合的理念,开发出一种新型的混合装置／结晶器。其具有低剪切应力无搅拌混合和达到固体颗粒的均匀悬浮。在完成新型混合装置的冷模设计加工后,测定了它的流型;并用脱色法测定了甘油与水调配出不同中高粘度的流体的混合时间;通过测定不同振动频率下的混合时间的变化,绘制出混合时间变化曲线,从而可确定最佳的操作条件;通过加入不同密度的固体颗粒,模拟结晶过程的固体相悬浮状况。这种新型混合装置具有较高的实用价值,市场前景广阔。     

A CFD model for predicting the flow patterns of viscous fluids in a bioreactor under various operating conditions

Computational fluid dynamics simulation is becoming an increasingly useful tool in the analysis and design of simultaneous saccharification fermentation (SSF) and saccharification followed by fermentation process (SFF). To understand and improve mixing and mass transfer in a highly viscous non-Newtonian system, it was necessary to simulate the flow behavior in this bench scale bioreactor (BioFlo 3000). This study focused on designing a high concentration medium agitation system for such a process using the commercial computational fluid dynamics package Fluent (V. 6.2.20) and its preprocessor Mixsim (V. 2.1.10). The objective of this study is to compare performance of various designs of a bioreactor and identify the flow pattern and related phenomena in the bench scale tank. The configuration of the physical model for simulating a mixing tank with a Rushton impeller consists of an ellipsoidal cylindrical tank with four equally spaced wall mounted baffles extending the vessel bottom to the free surface, stirred by a centrally located six-blade Rushton turbine impeller. Simulations were performed with the original and a modified design in which the lower bottom shaft mounted a Lightnin A200 impeller. The results suggest that there is a potential for slow or stagnant flow between top impellers and bottom of the tank region, which could result in poor nitrogen and heat transfer for highly viscous fermentations. The results also show that the axial velocity was significantly improved for the modified geometry in the bottom of the tank.     

磷酸陈化槽内桨叶高度对颗粒悬浮特性影响的数值模拟

以磷酸陈化槽为研究对象,使用计算流体力学软件FLUENT对陈化槽内的磷石膏固体颗粒的悬浮特性进行了数值模拟,模拟结果表明在高搅拌转速条件下,过大或过小的桨叶离底高度都不利于颗粒悬浮,搅拌功率随着桨叶的离底距离先增大,然后趋于稳定,但是离底距离对搅拌功率的影响较小,可以忽略不计,结合搅拌槽内固相的浓度分布情况,得出相对最好的桨叶离底距离为陈化槽直径的0.33倍。     

Validation of Solids Suspension Viscosity Measurements Using Computational Fluid Dynamics

Accurately measuring the viscosity of a solids suspension requires uniform suspension of the solids in the viscometer cup. In a cup‐and‐impeller viscometer system, solids may settle when the impeller speed is too low, causing viscosity measurements to appear lower than that of a well‐suspended slurry. Pre‐mixing of a solids suspension is typically performed to achieve steady state prior to measurements. Data here shows that the measured viscosity values differ depending on the pre‐mixing speed, indicating that the solids are not properly suspended at all speeds. A commonly used cup‐and‐vane impeller system can be thought of as a mixing tank that should operate above the uniform‐suspension speed (USS), although determining the USS experimentally is rather subjective. Computational fluid dynamics (CFD) is employed here to determine the USS of a pretreated corn stover (PCS) solids suspension and to confirm the experimentally measured USS.     

Segregated regions in continuous laminar stirred tank reactors

Using visualization techniques, including acid/base reactions and UV fluorescence, we provide experimental evidence of segregated regions (islands) during mixing of viscous Newtonian fluids under laminar flow conditions in continuous stirred tank reactors (CSTRs). The effect of inlet/outlet stream position and Reynolds number on the dynamics of the mixing processes is examined. Numerical experiments in 3-D map were able to capture the main features of the CSTR flow by perturbing a Batch system using an imposed axial flow. Asymmetric flow patterns produced by off-center positioning of inlet and outlet pipes cause a reduction in size of the segregated region, enlarging the chaotic region and leading to more efficient mixing. Under dynamic inlet flow conditions, the laminar steady flow is perturbed, giving rise to an asymmetric flow pattern that is able to destroy toroidal segregated regions. Counter-intuitively, higher agitation speed (higher Re) did not enhance overall mixing efficiency. Faster agitation stabilized the toroidal regions, making it harder to destroy them. In addition, dynamic mixing protocols are investigated to enhance mixing performance. We demonstrate that time-dependent pumping and stirring protocols are able to efficiently destroy long-lasting toroidal regions.     

搅拌生物反应器混合特性的数值模拟与实验研究

以工程流体计算软件CFX-4.4为工具,对不同规模的机械搅拌生物反应器的混合特性进行数值模拟,研究了不同操作条件下反应器混合时间的变化规律. 采用pH电极在位监测[H+]的方法实验测定混合时间. 模拟结果与实验测定值之间的误差随反应器容积增大而逐渐减小,对容积为25 m3的反应器误差小于11.6%.     

柠檬酸发酵高效轴向流搅拌反应器的中间试验

基于影响搅拌生物反应器的非生物参数、生物参数及流变学特性的分析研究,开发了高效轴向流搅拌生物反应器。该反应器具有流体混合均匀、氧传递速率快、转化率高和功耗低等优点。该反应器用于柠檬酸发酵中试研究,结果表明:在使用原菌种及发酵工艺的基础上,使产酸增加7.6%,转化率提高18.9%,发酵周期下降31%,产酸速率提高56%,功耗下降29%。     

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.     

混合澄清槽内离子液体体系的三相流体动力学模拟

离子液体是近年来被广泛研究的新兴绿色溶剂,其在乏燃料后处理技术中具有潜在的工业应用前景。但由于缺乏对萃取反应器中离子液体流动特性的研究,制约了离子液体萃取体系的实际应用。本文以萃取工艺中广泛应用的混合澄清槽为对象,以去离子水及1-丁基-3-甲基咪唑双(三氟甲磺酰)亚胺盐（[C₄mim][NTf₂]）分别作为水相及有机相,考虑上层空气对流动行为的影响,对其混合室进行计算流体力学（computational fluid dynamics, CFD）模拟,考察不同转速、流比及温度下的有机相分布、压力场、湍动程度等。结果表明,模拟结果较好地符合实验结果,且最大误差小于6.3%;转速能直观地提升混合性能,但当超过500r/min后,继续提高转速将显著增大出口气量,从而可能对澄清室的分相性能提出更高要求;增大流比、升温均能提升350r/min转速下的有机、水相混合能力,升温还有效减小了桨力矩,但当温度超过303K时,继续升温对于桨力矩、有机相速度的改变不明显。因此,实际工艺条件建议结合升温与转速调节,在实现较好混合性能的同时,减少对澄清室分相性能的要求。本文在建立离子液体三相体系数值模拟方法的同时,为混合澄清槽的工况优化提供合理建议,并为离子液体萃取体系的深入研究提供了参考。     

Industrial mammalian cell culture

A number of proteins with potential therapeutic uses (monoclonal antibodies, interferons, plasminogen activators) have been produced in mammalian cells. Novel bioreactor designs used to generate high density cultures mostly employ methods which approximate in vivo homeostasis. These perfusion and dialysis culture systems maintain the concentration of medium components and growth factors at a relatively high level while minimizing the accumulation of growth inhibitory metabolites. These methods include microcarrier culture, microencapsulation and other forms of entrapment, perfusion suspension culture in continuous stirred tank reactors, hollow fibres and combinations thereof. A summary of the status of industrial mammalian cell culture will be presented with examples illustrating the processes above.     

微载体与片状载体培养MDCK-G1细胞的比较

目的比较微载体与片状载体培养MDCK-G1细胞的效果。方法在7. 5 L生物反应器中,分别使用微载体和片状载体培养MDCK-G1细胞,比较细胞的贴壁效率,并对搅拌转速、初始细胞接种密度、载体量进行优化。结果微载体最适培养条件为搅拌转速55 r/min,初始细胞接种密度3×10^5个/mL,载体量8 g/L,在此条件下最高细胞密度为(5. 03±0. 12)×10^6个/mL;片状载体最适培养条件为搅拌转速120 r/min,初始细胞接种密度2×10^5个/mL,载体量200 g,在此条件下最高细胞密度为(10. 22±0. 69)×10^6个/mL。结论片状载体能够用于MDCK-G1细胞的培养,且相对于微载体可获得更高的细胞密度,但有不易放大的缺点,作为细胞培养系统进一步开发具有很大的应用潜力。     

低高径比气升式环流反应器数值模拟分析

气升式反应器因其结构简单，有良好的混合传热性能，便于操作等优点已广泛用于化工、生物化工等行业。利用商用计算流体力学软件Fluent，利用Euler—Euler双流体模型，重点针对好氧反应的特点，对一种具有低高径比（H/D=1．67）的环流气升式反应器内的气液两相流动及混合性能进行研究，描述出反应器内气含率和环流液速等参数的详细分布，分析模拟结果，气液速度分布和气含率分布等与实际情况基本吻合，从而证实了计算结果的有效性，为工业实际应用提供一定参考。