The limited understanding of intricate mesoscale bubble structures in stirred tank reactors under forced convection poses significant challenges to the design and optimization of related agitation systems. In this study, the coupled level set with volume of fluid (CLSVOF) method is employed to investigate bubble dynamics and macroscopic hydrodynamics in a gas–liquid stirred tank after model validation. The results demonstrate that: i) based on the dynamics of bubble clusters within the system, the stirred tank can be categorized into four distinct regions: the dispersal region, accumulation region, rising wall-region, and reflex region; ii) in the dispersal region, the rear of impeller blade generates large-scale vortex. Two merging modes are identified during the bubble rupture process: the merging of bubbles at adjacent orifices and the merging of discrete bubbles with the back of impeller blade due to negative pressure. Two bubble breakup modes are observed: bubble breakup at the back of the impeller blade due to stretching and the breakup of bubbles growing at orifices due to disturbance caused by the impeller blade; iii) the inertial forces predominantly control most bubbles in the system. A predictive correlation for bubble velocity is proposed; iv) elevating the stirring speed increases bubble number in the accumulation region. Moreover, enlarging gas flow rate and fluid viscosity leads to a discernible augmentation of overall bubble size; v) at the macroscopic scale, the radial, axial, and tangential velocities of the system exhibit an increase with enlarging stirring speed, while showing no significant change with the increase in gas flow rate. Additionally, as fluid viscosity and density increase, the flow undergoes a transition from turbulent flow to laminar flow.

中文翻译：

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基于CLSVOF方法的折流板搅拌槽流体动力学和气泡动力学空间特性研究


对强制对流下搅拌釜反应器中复杂的介观气泡结构的了解有限，这对相关搅拌系统的设计和优化提出了重大挑战。在本研究中，模型验证后，采用水平集与流体体积耦合（CLSVOF）方法研究气液搅拌罐中的气泡动力学和宏观流体动力学。结果表明：i）根据系统内气泡团的动力学特征，搅拌槽可分为四个不同的区域：扩散区域、聚集区域、上升壁区域和反射区域； ii) 在分散区域，叶轮叶片后部产生大规模涡流。气泡破裂过程中存在两种合并模式：相邻孔口处的气泡合并以及离散气泡由于负压而与叶轮叶片背面合并。观察到两种气泡破裂模式：叶轮叶片后部因拉伸而破裂的气泡和因叶轮叶片引起的扰动而在孔口生长的气泡破裂； iii) 惯性力主要控制系统中的大部分气泡。提出了气泡速度的预测相关性； iv) 提高搅拌速度会增加聚集区的气泡数量。此外，增大气体流速和流体粘度会导致整体气泡尺寸明显增大； v)在宏观尺度上，系统的径向、轴向和切向速度随着搅拌速度的增大而增大，而随着气体流量的增大而没有明显变化。 此外，随着流体粘度和密度的增加，流动会经历从湍流到层流的转变。