气液搅拌槽内气泡尺寸与局部气含率的CFD模拟

采用在欧拉-欧拉双流体模型的基础上耦合气泡数密度（BND）函数模型,引入气泡破碎和聚并函数,对双层组合桨气液搅拌槽内的气泡尺寸和局部气含率进行了计算流体力学（CFD）模拟,同时采用双电导电极探针法对搅拌槽内局部气液分散特性进行了实验测量,并和CFD模拟结果进行了对比.结果表明：较高通气量条件下搅拌槽内气泡尺寸和局部气含率分布很不均匀,气泡尺寸在叶轮排出流区较小,且沿着排出流方向逐渐增大；在两桨间区域和上层桨以上区域气泡以聚并为主；局部气含率在循环涡涡心、叶轮和挡板后部较高,叶片后部存在明显气穴.

computational fluid dynamics simulation of bubble size and local gas holdup in stirred vessel

The bubble size and local gas holdup in a stirred vessel with dual impellers were simulated numerically with computational fluid dynamics, in which the Euler-Euler multiphase flow model, multi-reference frame method and a transport equation for bubble number density (BND) function were combined. The effects of bubble coalescence and breakage were involved in the bubble number density function. The numerical results were in good agreement with the experimental values measured with double-tip conductivity probes. The results show that the bubble size and local gas holdup distribution in the stirred vessel are very non-uniform under relatively high superficial gas velocity. The bubble sizes in the impeller discharge region is quite small and increases with the discharge currents of the impeller. Bubbles coalescences play a dominant role in the inter-impeller region and the region above upper impeller. Local gas hold up is much high just behind the baffles and the blades where cavitation forms and in the centre of circulation loop.