Abstract: All experiments were carried out in a transparent dished bottom stirred tank with the diameter T of 0.48 m and liquid level of 0.6T. The power consumption and mixing performance of a coaxial mixer consisting of a wall-scraping anchor and different dispersion impellers (CBY, 45o pitched blade turbine and Rushton turbine) operating in co- and counter-rotating modes were experimentally characterized in viscous Newtonian fluids with different viscosities. The results show that for the co-rotating dispersion modes, the power consumption of the anchor could decrease up to 10% of that for anchor rotating only, whereas for the counter-rotating dispersion ones, it could increase 2 times of that for anchor rotating only. The power consumption of the dispersion impellers is almost independent of the anchor rotation. The new correlations based on the impeller geometry and speed ratios for the generalized Reynolds number and the power number are proposed, and a reasonable power curve can be generated for different experimental speed ratios of each system. Impellers in co-rotating mode are more efficient than the counter-rotating ones in the mixing of the Newtonian fluids. Among above three dispersion impellers, the power consumption of the CBY impeller-anchor combination is about 20% to 30% of that for other two combinations given the similar mixing performance.

Key words: Newtonian fluid, coaxial mixer, power consumption, mixing time, mixing characteristic

摘要： 在直径0.48 m的椭圆底搅拌槽内，液位与槽径比(H/T)为0.6，采用不同粘度的牛顿流体糖浆溶液，研究了分别以CBY, 45o四斜叶桨及Rushton涡轮桨作为快速分散桨、锚式桨作为慢速桨构成的同心双轴搅拌系统，在快、慢速轴同向和异向2种旋转方式操作时的功率特性和混合性能. 结果表明，分散桨对锚式桨的功率消耗影响较大. 两轴同向旋转时，分散桨会使锚式桨的功耗降低，转速比RN增加，降低幅度也增大，RN=14时，锚式桨功率可降至单独旋转时的约10%；异向旋转时锚式桨的功率随RN增加而增加，RN=14时，锚式桨功率可增至单独旋转时的2倍左右. 但锚式桨对分散桨的功率消耗影响很小，在±5%以内. 计算同心双轴复合搅拌系统的复合功率准数和复合雷诺数关系时考虑了RN的影响，使在实验条件下不同转向及RN的功率曲线较好吻合. 混合效果同向旋转优于异向旋转，在牛顿流体中，达到相同混合效果时，CBY桨的能量消耗仅为其他2个分散桨的20%~30%.

关键词: 牛顿流体, 同心双轴搅拌器, 搅拌功率, 混合时间, 混合特性