Abstract: Based on the characteristics of structure and operation of coaxial mixer, a three dimensional mathematical model considering the flow and mixing process was developed.A novel coaxial mixer consisting of different combined inner impellers with upper and lower blades and outer wall-scraping frame was simulated and its power consumption, flow field and mixing characteristics in a highly viscous Newtonian fluid under co-rotating and counter-rotating modes were obtained.The results show that the total power consumption is less and the mixing efficiency is higher under co-rotating mode.The power consumption of outer impeller is largely influenced by combined inner impeller, which decreases with the increase of speed of inner impeller under co-rotating mode and increases under counter-rotating mode.For the combined inner impeller composed of turbine paddles, the specific volumetric mixing energy with the same Reynolds number is less when the diameter ratio between the inner impeller and stirred vessel is about 0.35.For highly viscous Newtonian fluids, the coaxial mixer with combined inner impeller with upper two-pitched-blade turbine and lower two-straight-blade turbine is better only when the Reynolds number in the mixing system is below 36; otherwise, the combined inner impeller with upper six-pitched-blade turbine and lower six-straight-blade turbine consumes less energy.

Key words: coaxial mixer, combined impeller, power consumption, mixing characteristic, numerical simulation

摘要： 基于同心双轴搅拌器的结构与运行特点,建立了兼顾其流动、混合过程的三维数学模型,并以过程工业应用较多的两种不同尺寸双层组合桨作为内桨、框式桨作为外桨构成的同心双轴搅拌器为研究对象,数值模拟了其在中高黏牛顿流体中同向及反向转动模式的功率特性、流场特性及混合特性。模拟结果表明,同向转动模式下,整个系统的搅拌功耗更小、混合效率更高;外桨功耗受内桨影响较大,一般随内桨转速的增大,恒速外桨的功耗同向转动时会减小、反向转动时会增大;对由桨式搅拌器构成的组合式内桨而言,当内桨直径与釜体直径之比为0.35左右时,相同Reynolds数下的单位体积混合能更小;中高黏牛顿流体中,同心双轴搅拌器的内桨采用上层六斜叶桨+下层六直叶桨的组合形式时更高效节能,仅在体系Reynolds数小于36时,上层二斜叶桨+下层二直叶桨的内桨组合形式才具有相对优势。

关键词: 同心双轴搅拌器, 组合桨, 搅拌功率, 混合特性, 数值模拟