Abstract:

The scale-up of the industrial mixer is always based on operation experience, and lacks theoretical basis. In this paper, effects of scale-up criteria on the mixing time and flow characteristic in the intermittent pump-mixer with single-phase has been studied. Three-dimensional time-dependent mixing prediction has been carried out using multi reference frames (MRF) method and standard k-ε model embodied by computational fluid dynamics (CFD) package FLUENT6.3. The results indicated that the calculated mixing time was depended on detecting location, but the dependency became weaker by increasing the impeller speed. The power number was obtained at different Reynolds number, and it tended to be a constant as 1.3 under the condition of sufficient turbulence. Geometric similarity ensured the axial flow characteristics in the mixer. The criterion of equal impeller tip speed and equal Reynolds number demanded a longer mixing time and obtained a lower suction pressure head than the benchmark mixer. The criterion of equal circulation time and geometrical similarity could obtain the same mixing time as the benchmark and high suction pressure head, but the power consumption per unit volume sharply increased to 24 times as the benchmark. The criterion of equal power consumption per unit volume and geometrical similarity could obtain a better balance of all the parameters considered, and was considered to be the best one compared with other three criteria.

Key words: scale-up, mixing, CFD, pump-mix mixer, mixing time

摘要：

工业混合澄清槽混合室的放大设计多基于操作经验,缺乏理论基础。基于几何相似放大,采用计算流体力学(CFD)方法,针对间歇操作的单相体系,对4 种不同放大准则下混合室内混合时间和流场特性的变化规律进行研究。结果显示,混合时间的计算值与测量位置有关,但随转速的增加受测量位置的影响减小;充分湍流条件下,本研究体系的功率准数趋于常数N_P=1.3,且几何相似放大可以保证混合室中轴向流动的流型特征;等桨叶端面速度和等Reynolds 数准则下,所需混合时间长,且抽吸压头小;等循环时间准则下,可以得到与基准混合室相同的混合时间和较高的抽吸压头,但单位体积功耗急剧增加到基准槽的24 倍;等单位体积功耗准则下,在满足具有较低的混合时间和较高的抽吸压头的同时还保证了较低的单位体积功耗,优于其他3 种放大准则。

关键词: 放大, 混合, 计算流体力学, 混合室, 混合时间