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1.
搅拌槽内粘稠物系的混合过程   总被引:5,自引:0,他引:5  
以发酵罐中通气搅拌下的混合为背景,考察了搅拌形式,物系流变性质及通气速率等因素,对搅拌槽内粘稠物质系中混合过程的影响,轴向流翼型混合效率高于涡轮桨,通气有助于改善粘稠物系中的混合粘度变化主要改变槽内流动状态和桨叶泵送能力,从而改变混合效率,当物系为中等粘度假塑性流体时,混合速率由桨叶泵送流动的流量和形态所决定,多层搅拌下分区现象限制了混合速率。  相似文献   

2.
从实验和数值模拟两方面对搅拌槽内中高黏物系条件下的气含率、气泡尺寸大小和传质特性等进行综述。讨论了搅拌桨型、操作条件、黏度或非牛顿性对气液分散特性的影响。阐明了径流式搅拌桨和上翻式轴流桨的组合能减小气穴,更适合中低黏物系的搅拌;搅拌转速比通气量的影响效果更明显,转速增加使气泡的分布均匀性变好,而提高通气速度会产生大气泡,使气泡分布不均匀程度增加;黏度或非牛顿性的增加可以改变气泡的碰撞频率,气泡平均尺寸减小。最后讨论了针对中高黏物系的计算流体力学模型的修正方法,并且展望了此领域的研究发展方向。  相似文献   

3.
搅拌槽中液-液-固三相传质的实验研究   总被引:2,自引:0,他引:2  
选择欧洲化学工程师协会(EFCE)推荐的典型液-液萃取体系正丁醇-丁二酸-水,加入不同粒径的玻璃珠构成液-液-固三相传质,以去离子水为连续相,正丁醇为分散相,溶质丁二酸从分散相向连续相传质. 利用电导率法测定液-液相传质系数,并考察了搅拌转速、固体质量百分含量、不同桨型(标准Rushton桨、上推式和下推式45°六折叶涡轮桨)、桨中心平面距槽底距离以及固体颗粒粒径对相间传质的影响. 结果表明,在高转速时,惰性固体粒子的存在强化液-液体系的传质. 随着惰性固体含量增大,液-液-固三相传质有一极大值. 粒径大于100 μm 的固体粒子对液-液体系传质系数影响很小. 三种桨中Rushton桨的对流传质效果最好.  相似文献   

4.
冯尧成  任厉泰  张锋  张志炳 《化工学报》2020,71(11):4936-4944
微生物好氧发酵过程是一个多相生化反应体系,空气中的氧在气液两相间的传质速率对生化发酵过程有重要影响。而气泡中氧的传递特性是气泡的形态、运动及体系温度、压力和物性综合影响的结果。通过建立两组分空气气泡上升及其氧传质耦合模型,进而采用数值模拟描述好氧发酵体系中微界面体系的强化效果。利用能量耗散理论评价制造微气泡体系的能耗,以获得高性价比的气泡形态和较高的氧利用率。计算结果表明,在预设的工况下,液面高度一定的反应器内,初始半径大于500 μm的气泡会在短时间内逸出体系,造成物料浪费;而气泡初始半径小于100 μm时,其停留时间、传质效率和氧利用率会显著提升。小气泡的生成需要较大的能耗,需要综合生产成本考虑。在不考虑其他因素影响的情况下,体系中的DO值如果维持在20%~30%,可以获得最大的氧气传质速率。  相似文献   

5.
一种新型曝气设备及其气液传质研究   总被引:1,自引:1,他引:0  
开发了一种叶片开孔曝气的新型搅拌设备,并以清水实验条件为基础,研究了该设备中气泡运动规律,选择传质理论中的溶质渗透模型,从单个气泡的产生到上升至液面这一过程入手,建立传质速率方程,进而分析了容器中气泡整体的分布状况,得出总的理论瞬时氧传质速率方程,用来分析和研究该类设备的气液传质效率,为设计高效的曝气设备提供理论基础。  相似文献   

6.
在 50L卧式搅拌釜内,采用氧电极法测量纯水 O2 体系的液侧容积传质系数kLa, 研究搅拌弗鲁德数Fr、桨叶尺寸和液含量等对kLa的影响。随着Fr提高,kLa增大;桨径、桨宽、叶片数和层间距与kLa有关系,而层间夹角对kLa影响不大;随液含量的增加kLa先缓慢升高而后降低,且峰形和峰值随Fr的增大而发生变化。研究结果可供四氟乙烯等聚合釜搅拌桨设计优化和工程放大参考。  相似文献   

7.
很多废水处理装置涉及非牛顿型流体中的多相流动和传质问题,研究其中的气液传质过程有助于实现装置的优化设计和高效节能运行。以鼓泡反应器内清水和不同质量分数的羧甲基纤维素钠(CMC)水溶液为实验对象,分别研究气相表观气速和液相流变特性对气泡尺寸分布、全局气含率和体积氧传质系数的影响。实验结果表明,液相的流变特性对其传质特性参数均有较大影响。与清水相比,CMC水溶液中气泡平均直径和分布范围更大;清水和CMC水溶液的全局气含率均随表观气速的增加而增大;CMC水溶液的体积氧传质系数随CMC水溶液质量分数的增加而减小。基于实验研究,得出修正的体积氧传质系数公式和适用于幂律型非牛顿流体流动体系氧传递过程的无量纲关联式,可很好地实现非牛顿流体流动的废水处理装置中气液传质参数的计算。  相似文献   

8.
微气泡具有气液接触面积大、气体溶解速率快、上升速度慢和水中停留时间长等理化特征,非常适合于高气液传质效率需求的生物发酵过程。本文介绍了能够耦合生物反应器的几种微气泡发生装置,分别为微气泡分散器、微孔膜、流体振荡器耦合微孔膜和微气泡曝气搅拌桨;并简述了微气泡发生装置耦合搅拌式生物反应器、气升式生物反应器和生物膜反应器在生物反应过程的应用进展;最后回顾了二氧化碳微气泡在生物反应器的应用研究进展。指出微气泡耦合生物反应器的研究仍处于起步阶段,在放大规律和能耗方面仍处于研究空白。微气泡耦合生物反应器的发展对工业生物技术、石油化工、污水处理和资源再利用等的发展具有重要的意义。  相似文献   

9.
在实验室提出的新型三相搅拌槽——自吸式龙卷流型搅拌槽中,采用六直叶圆盘涡轮桨进行三相混合性能的实验。从固液悬浮、气液分散和传质性能等方面对搅拌槽进行了研究,探讨了固相颗粒对气含率和传质性能的影响,得到了搅拌槽中不同性能参数的变化规律。结果表明:自吸式龙卷流型搅拌槽作为一种新型的三相搅拌槽,能够获得良好的固液悬浮和气液分散效果;当搅拌槽内固相体积分率较低(φ20%)时,可采用颗粒的壁面堆积高度作为完全悬浮状态的判定标准;固相颗粒的存在会使气含率明显降低,但对传质性能的影响较为复杂,φ5%时的体积传氧系数K L a高于纯溶液,φ5%时的K L a低于纯溶液,但都随固相体积分率的增加而降低。  相似文献   

10.
在实验室提出的新型三相搅拌槽——自吸式龙卷流型搅拌槽中,采用六直叶圆盘涡轮桨进行三相混合性能的实验。从固液悬浮、气液分散和传质性能等方面对搅拌槽进行了研究,探讨了固相颗粒对气含率和传质性能的影响,得到了搅拌槽中不同性能参数的变化规律。结果表明:自吸式龙卷流型搅拌槽作为一种新型的三相搅拌槽,能够获得良好的固液悬浮和气液分散效果;当搅拌槽内固相体积分率较低(φ<20%)时,可采用颗粒的壁面堆积高度作为完全悬浮状态的判定标准;固相颗粒的存在会使气含率明显降低,但对传质性能的影响较为复杂,φ<5%时的体积传氧系数K L a高于纯溶液,φ>5%时的K L a低于纯溶液,但都随固相体积分率的增加而降低。  相似文献   

11.
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。  相似文献   

12.
Mixing efficiency in two-phase gas–liquid agitated vessel is one of the important challenges in the industrial processes. Computational fluid dynamics technique (CFD) was used to investigate the effect of four different pitched blade impellers, including 15°, 30°, 45° and 60°, on the mixing quality of gas–liquid agitated vessel. The multiphase flow behavior was modeled by Eulerian–Eulerian multiphase approach, and RNG kε was used to model the turbulence. The CFD results showed that a strong global vortex plays the main role on the mixing quality of the gas phase in the vessel. Based on the standard deviation criterion, it was observed that the axial distribution of the gas phase in the 30° impeller is about 55% better than the others. In addition, the results showed that the 30° impeller has a uniform radial distribution over the other impellers and the maximum gas phase holdup in the vessel. Investigation of the power consumption of the impellers showed that the 30° impeller has the highest power consumption among the other pitched blade impellers. Also, examine the effect of same power condition for pitched blade impellers showed that the 30° impeller has the best mixing quality in this condition.  相似文献   

13.
Gas hold-up and volumetric oxygen transfer coefficient were studied in a gas-liquid contactor without baffles, containing multiple impellers with four delta-type blades. The blades of each adjacent impeller were offset by 45° in an alternating manner. The direction of rotation of the impellers periodically was reversed. This new type of agitated gas-liquid contactor was denoted as “AJITER”. The effects of the gas sparging rate, the forward-reverse agitation rate and the number of impellers on the gas hold-up and volumetric oxygen transfer coefficient in the AJITER when different types of gas spargers were used were evaluated experimentally for an air-water system. Empirical relationships are presented to predict the gas hold-up and volumetric oxygen transfer coefficient. The differences in performance between the AJITER and existing types of gas-liquid contactors are discussed in terms of the differences in the gas hold-up and volumetric oxygen transfer coefficient due to changes in the superficial gas velocity.  相似文献   

14.
Mixing efficiency in two-phase gas-liquid agitated vessel is one of the important challenges in the industrial processes. Computational fluid dynamics technique (CFD) was used to investigate the effect of four different pitched blade impellers, including 15°, 30°, 45° and 60°, on the mixing quality of gas-liquid agitated vessel. The multiphase flow behavior was modeled by Eulerian-Eulerian multiphase approach, and RNG k-ε was used to model the turbulence. The CFD results showed that a strong global vortex plays the main role on the mixing quality of the gas phase in the vessel. Based on the standard deviation criterion, it was observed that the axial distribution of the gas phase in the 30° impeller is about 55% better than the others. In addition, the results showed that the 30° impeller has a uniform radial distribution over the other impellers and the maximum gas phase holdup in the vessel. Investigation of the power consumption of the impellers showed that the 30° impeller has the highest power consumption among the other pitched blade impellers. Also, examine the effect of same power condition for pitched blade impellers showed that the 30° impeller has the best mixing quality in this condition.  相似文献   

15.
The gas flow in a 3:1 aspect ratio vessel agitated by triple Rushton turbines has been measured by an ultrasound Doppler probe and by means of residence time studies. Strong recirculation around each impeller is found which fits in well with the compartmentalisation found in earlier liquid mixing studies. Surprisingly, when two axial A315 impellers above a Rushton turbine were used, gas recirculation around each impeller was still found. Study of the liquid phase mixing by a decolourisation technique confirmed that the gas flow essentially destroyed the strong axial liquid flow expected. Indeed, even under unaerated conditions, compartmentalisation was found between each impeller.  相似文献   

16.
Volumetric mass transfer coefficient, power input, and gas holdup are key parameters in the design of mechanically agitated gas‐liquid contactors. Although the majority of industrial batches are of higher viscosity, reliable transport characteristics correlations for viscous batches are lacking in literature. These correlations are often based on the power input as the scale of energy dissipation. In order to develop reliable power input correlations, its measurements were carried out in a pilot‐plant vessel using multiple impellers of various types and diameters. Power input correlation shapes providing the best match with the comprehensive database are also expected to predict most precisely the impeller power in industrial‐scale vessels.  相似文献   

17.
Mixing time measurements were made in 300 and 1000 mm i.d. mechanically agitated contactors with different types of impellers, located at different heights from the bottom of the vessel. Mixing time measurements were also made in 150, 200, 385 and 1000 mm i.d. bubble columns with varying liquid heights. Transient pH measurement and conductivity measurement were used to measure the mixing times. Impeller speed was varied in the range of 3.33–20 r/sec in the case of mechanically agitated contactors and gas superficial velocity was varied in the range of 10–250 mm/sec in bubble columns. Effect of physical properties of the fluid (surface tension, ionic strength, liquid viscosity) and that of the non-Newtonian behavior on mixing time was studied. Mixing time in the presence of drag reducing agents was also investigated.In the range of variables covered in this work mixing time in mechanically agitated contactors and bubble columns was found to be in the range of 4–6Mixing time predictions based on the longest loop length and circulation velocity are made in the presence and absence of a gas for mechanically agitatA procedure is given for the prediction of the critical impeller speed for gas phase dispersion in mechanically agitated contactors.  相似文献   

18.
In the present paper, two gas‐liquid stirred tanks, one agitated by a radial impeller and another by an axial impeller, are modelled using the open‐source computational fluid dynamic (CFD) package OpenFOAM (open source field operation and manipulation). The combined effect of the bubble break‐up and coalescence in the tank is considered by a population balance model (PBM) called extended quadrature method of moments (EQMOM). The three‐dimensional simulation is made using a multiple reference frame (MRF), a well‐established method for the modelling of mixers. Dispersed gas and bubble dynamics in the turbulent flow are modelled using the Eulerian‐Eulerian approach (E‐E) with mixture k‐epsilon turbulent model and the modified Tomiyama drag coefficient for the momentum exchange. The model is developed to predict the spatial distribution of gas phase fraction, Sauter mean bubble diameter (), number density function (NDF), dissolved oxygen (DO) evolution, and flow structure. The numerical results are compared with experimental data and a fair agreement is achieved. The results of the axial impeller are discussed based on four impeller rotational speeds with different volumetric mass transfer coefficients.  相似文献   

19.
The behaviour of gas–liquid mixtures in the vicinity of the blades of an unsteadily rotating impeller in an unbaffled agitated vessel was studied by observations made with a rotating camera. The impellers used were a disk turbine impeller with six flat blades (DT) and a novel cross‐type impeller with four delta blades (CD). The behaviour of gas–liquid mixtures near the blades of the forward–reverse rotating impeller was unsteady in terms of the formation of cavities behind the blades and their dispersion into gas bubbles, and differed from that near the blades of a unidirectionally, steadily rotating impeller. The differences in relative power consumption between the forward–reverse rotating impellers in the unbaffled vessel and the steadily rotating impellers in the baffled vessel are discussed in relation to the differences in the behaviour of gas–liquid mixtures near the blades of each rotating impeller. © 2002 Society of Chemical Industry  相似文献   

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