Understanding dispersion behaviour of bubbles emitting from a sparger is a critical element of mineral flotation process. This aspect was investigated in the present study involving a bubble plume in a semi-batch rectangular column in the presence of an anionic surfactant. First, high-speed imaging was used to visualise the bubble plume behaviour at different air flow rates (0.1 – 0.5 L/min). An image processing code was developed to determine the mean bubble diameter which indicated a decrease in the mean bubble diameter from ∼ 0.60 mm to 0.51 mm with increasing gas flow rates. A transient 3D Eulerian-Eulerian multiphase CFD model with a bubble population balance sub-model was also developed to quantify the gas holdup and turbulence energy dissipation rate distribution in this system utilising the experimentally measured mean bubble size. Experimentally, it was observed that symmetry of the bubble plume was disrupted at higher gas flow rates leading to larger dispersion of gas bubbles towards the top of the column. This observation was explained by the CFD model which predicted asymmetric transverse velocity profiles that increased in the axial direction. The model also predicted increasing gas holdup in the system (∼0.02 to 0.11) with increasing gas flow rates. The corresponding turbulence energy dissipation rate increased from ∼ 0.014 to 0.076 m2/s3 with maximum turbulent energy dissipation rate occurring near the gas distributor zone. Also, a transition from a bubbly to a distinct foam zone was noted at the free surface in the higher gas flow rate cases which was explained by the turbulence energy dissipation rate in the system.

中文翻译：

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在表面活性剂存在下，上升气泡羽流中气体扩散的动力学


了解喷射器喷出的气泡的分散特性是矿物浮选过程的关键要素。在本研究中研究了这方面，涉及在阴离子表面活性剂存在下半间歇矩形柱中的气泡羽流。首先，使用高速成像来可视化不同空气流速 （0.1 – 0.5 L/min） 下的气泡羽流行为。开发了一个图像处理代码来确定平均气泡直径，这表明随着气体流速的增加，平均气泡直径从 ∼ 0.60 mm 减小到 0.51 mm。还开发了一个瞬态 3D Eulerian-Eulerian 多相 CFD 模型，其中包含气泡种群平衡子模型，以利用实验测量的平均气泡尺寸来量化该系统中的气体滞留和湍流能量耗散率分布。实验观察到，在较高的气体流速下，气泡羽流的对称性被破坏，导致气泡向塔顶的更大分散。CFD 模型可以解释这一观察结果，该模型预测了在轴向增加的不对称横向速度分布。该模型还预测了随着气体流速的增加，系统中的气体滞留量会增加（∼0.02 到 0.11）。相应的湍流能量耗散率从 ∼ 0.014 增加到 0.076 m2/s3，最大湍流能量耗散率发生在气体分配区附近。此外，在较高气体流速的情况下，在自由表面观察到从气泡区到明显泡沫区的转变，这可以通过系统中的湍流能量耗散率来解释。