Chaotic And Stiring Characteristics Of Flow Field Of Pseudoplastic Fluid

As an important component of non-Newtonian fluids,pseudoplastic fluids play an important role in industrial production such as biochemistry,paper paddles,cosmetics and ploymers.It is of great significance to study the stirring flow field and mixing characteristics of different stirring blades for the optimization and improvement of the shape of the stirring blades and the energy conservation in the industrial production process.In this paper,the turbulence model of Standard k-? and the rheological model of power-law are used to simulate the chaotic flow field and analyze the mixing characteristics of the pseudoplastic fluid(Xanthan gum solution).In order to verify the correctness of the numerical simulation method,the flow field structure of the PIV experiment and the velocity at different heights in the stirred tank were compared with the numerical simulation of the flow field structure and velocity.The main conclusions of the simulation of pseudoplastic are as follows:(1)In the stirring flow field,the agitating vortex center of the 6PBT agitating paddle was asymmetrical structure not only up and down but also left and right;the vortex center of the 6BT agitating paddle was symmetrical from up and down and from left and right.The fluid at the blade tip of the 6PBT impeller was discharged in an oblique direction and the fluid at the blade tip of the 6BT impeller was discharged in a horizontal direction.At the same rotating speed,the speed of the 6PBT paddle was greater than the speed of the 6BT impeller at the same height in the tank.The shear strain rate of the 6PBT impeller was higher than that of the 6BT impeller.(2)With the increase of the rotating speed,the change of the vortex position of the 6PBT and 6BT paddles moved in the radial direction toward the wall of the stirring tank.The change of viscosity cofficient of pseudoplastic fluid did not change the position of vortex center.The speed of impeller was the main factor affecting the mixing effect of the impeller.(3)The shape of the chaotic attractor was similar to the butterfly shape.At the same speed the pathline of the 6PBT impeller was more disordered than that of 6BT impeller.From the shape of the pathline,the mixing effect of the 6PBT impeller wasbetter than the mixing effect of the 6BT impeller.(4)From the stirring characteristics,the mixing time of the 6BT impeller was shorter than the 6BT impeller under the same stirring speed.The mixing energy per unit volume did not decrease with the increase of the rotating speed.The mixing efficiency of the 6PBT impeller was higher than that of the 6BT impeller.