管输剪切模拟搅拌槽中流体平均剪切率的计算

Estimation of average shear rate in stirred vessels for pipelining shear simulation

计算搅拌槽内流体剪切率的Metzner_Otto方法只适用于计算某些叶轮 搅拌槽系统内层流时叶轮区的平均剪切率 ,不能满足原油管输过程剪切作用模拟的需要。根据流体流动的能量耗散率与剪切率的关系 ,提出了通过搅拌的轴功率计算搅拌槽全槽流体平均剪切率的方法。针对牛顿流体和幂律流体 ,提出了全槽平均剪切率的计算式。以实验室用的一个小型搅拌系统为例 ,使用所提出的方法 ,建立了槽内流体平均剪切率与搅拌转速、流体体积、幂律流体稠度系数及流动特性指数关系的经验数学模型。该模型预测的结果与直接由实测扭矩计算的平均剪切率相当接近。本方法适用于各种类型的叶轮 ,不受流体流态的限制 ,其原理还适用于符合其他流变模型的非牛顿流体。

The existing Metzner_Otto equation for stirring shear rate estimation is only suitable for calculating the average shear rate around the impeller in the laminar flow of some impeller_vessel systems and cannot meet the requirement of shear simulation for the process of oil pipelining.On the basis of the relationship between the energy dissipation rate in the fluid flow and the shear rate,an approach is presented to estimate the whole_vessel average shear rate in a stirred vessel by using the shaft power of the stirrer. Some equations of shear rate estimation for Newtonian fluid and the power law fluid were derived.Taking a small stirring system used for laboratory test as an example, an empirical model to correlate the whole_vessel average shear rate and the stirring speed,fluid volume in the vessel, consistency coefficient and flow behavior index of the power law fluid was developed by using the present approach.The shear rates estimated by the empirical model are in good agreement with those calculated according to the measured torque of the shaft.This approach is available for different types of impeller and flow regime,and can also be applied to the non_Newtonian fluids favorable to other rheological models.