Background

A Forward-reverse rotating impeller was used in an unbaffled tank to improve the mixing efficiency. Flow field and power characteristics in the tank were numerically studied.

Methods

Computational fluid dynamics(CFD) simulations were performed to investigate hydrodynamics in the unbaffled tank. The Reynolds stress turbulence (RST) model along with a sliding mesh approach was used to predict instantaneous flow fields in the stirred tank.

Significant findings

Fluid in the unbaffled tank flows periodically with the forward-reverse impeller agitation. Zonal flow phenomenon was found for the fluid affected by agitation in different directions. The effects of operating conditions on instantaneous fluid velocity vary with positions in the tank. Flow field characteristics in the forward-reverse agitated unbaffled tank are very different from those in constant agitated unbaffled and baffled tanks. Generally, transient power consumption is only the function of its corresponding transient rotational speed. The averaged impeller power number is a constant and is not affected by maximum rotational speed and cycle time. The averaged power number is the largest in the unbaffled tank with forward-reverse agitation, followed by the baffled tank at a constant agitation, and the smallest in the unbaffled tank at a constant impeller speed.

中文翻译：

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正反转叶轮罐内流体动力学特性的CFD模拟

背景

无挡板罐体采用正反转叶轮，提高混合效率。数值研究了罐内的流场和功率特性。

方法

进行了计算流体动力学 (CFD) 模拟以研究无挡板水箱中的流体动力学。雷诺应力湍流 (RST) 模型与滑动网格方法一起用于预测搅拌罐中的瞬时流场。

重要发现

无挡板水箱中的流体随着正反转叶轮的搅拌而周期性地流动。对于受不同方向搅动影响的流体，发现了带状流动现象。操作条件对瞬时流体速度的影响随罐中的位置而变化。正反向搅拌无挡板罐中的流场特性与恒定搅拌无挡板和挡板罐中的流场特性有很大不同。一般来说，瞬态功耗只是其对应的瞬态转速的函数。平均叶轮功率数是一个常数，不受最大转速和循环时间的影响。平均功率数在前向反向搅拌的无挡板罐中最大，其次是在恒定搅拌下的挡板罐，