Abstract:

Bubble size distribution influences the separation efficiency of dissolved air flotation (DAF) while it is mainly affected by the coalescence phenomenon. In this study, both experiments and numerical simulation are performed to study the bubble coalescence in the contact zone of a DAF tank. By comparing the simulation results with experimental measurement data, the numerical simulation method based on population balance model is established to investigate the bubble coalescence behavior in the contact zone (c-zone). Luo aggregation model, Free molecular aggregation model and Turbulent aggregation model are adopted to predict the bubble size distribution (BSD), respectively. The results indicate that Turbulent aggregation model reproduces the BSD accurately and is more suitable for bubble coalescence simulation in the c-zone. During the flotation process, the bubble coalescence mainly takes place at the lower part of the c-zone and the bubble diameter does not change at the upper part of the c-zone. Besides, the addition of bubbles enhances the diffusion of flow with eddy occurring at the upper part and horizontal flow from the wall to the center at the lower part of the c-zone.

Key words: flotation, bubble, coalescence, computational fluid dynamics, population balance model

摘要：

气泡尺寸分布直接影响气浮分离效率,而聚并是导致气浮池内气泡尺寸变化的主要因素。首先用实验方法测量气浮接触区气泡尺寸分布,然后用计算流体力学方法对气泡/水两相流动及气泡聚并进行模拟,最后通过对实验和数值模拟结果进行对比建立基于相群平衡模型的浮选气泡聚并行为的模拟方法,分别运用Luo、Free molecular和Turbulent聚并模型对气浮接触区气泡聚并行为进行模拟。结果表明:Turbulent聚并模型计算所得气泡尺寸分布与实验值最接近,适合模拟接触区气泡聚并;气泡平均直径随高度升高先变大后保持不变,气泡聚并主要发生在接触区中下部;气泡的加入增强了接触区流动混乱程度,上部产生对称涡流,中下部呈由边壁向中心的水平流动。

关键词: 浮选, 气泡, 聚结, 计算流体力学, 相群平衡模型