Investigating the speed and geometry of the mixer on the flow distribution in an industrial reactor

Subject Areas : Journal of New Applied and Computational Findings in Mechanical Systems

Seyed mohammad hasan  Mousavizadeh ¹ (Mechanical Engineering - Islamic Azad University, Ahvaz Branch - Technical and Engineering Faculty)
Mahdi  Hamzehei ² (Assistant. Islamic Azad university , ahvaz Branch)

Received: 2023-07-20 Accepted : 2023-09-16 Published : 2023-08-23

Keywords: Stirred tank, CFD, Modeling, industrial reactor, Hydrodynamics,

Abstract :

In this project, a three-dimensional investigation of the fluid flow inside a stirred tank inside an industrial reactor has been done to investigate the velocity distribution and heat transfer. To model the stirred tanks and its blades, first the geometry structure was carefully studied, then the geometry modeling was done using SOLIDWORKS software, then the generated geometry was entered into the Ansys Space claim or Ansys Design Modeler software. After that, meshing is done with Ansys Meshing software, and then appropriate boundary conditions are applied on the stirred tank and its blades. In this project , SST , k-ω turbulence model is used. For meshing, unorganized mesh generation was used, and the average mesh quality, aspect ratio, and elongation for the computational mesh of the tank with an anchor agitator were 0.84, 1.84, and 0.22, and also the flow field inside an agitator tank with a baffle was For the angular speeds of 60 , 120 and 180 rpm , it was simulated for two types of stirrers. By increasing the angular speed of the propeller, the performance of mixers improves and better mixing takes place. Examining the velocity vectors showed that four strong wake regions were formed near the impeller, and two rings were formed on each side, one at the bottom and the other at the top of the stirrer. The first jet circulates to the bottom of the tank and then returns to the propeller area. The second fluid jet also circulates in the upward direction. In the new mixer, there are more high-speed areas in the distance between the bottom of the tank and the impeller compared to the anchor mixer. In fact, the speed is almost twice that of the anchor stirrer. Therefore, the new agitator has a much better performance than the anchor agitator in the bottom areas of the tank. So, the new mixer has a better performance for mixing solid materials that have the possibility of sedimentation. At distances farther from the bottom of the tank, the tank with the anchor stirrer has better mixing than the new stirrer , and this anchor stirrer has more high-velocity areas than the new stirrer. In the new high-speed mixer, the distance between the bottom of the tank and the propeller is greater than that of the anchor mixer. In fact, the speed is almost 2 times that of the anchor stirrer. Therefore, the new stirrer is much better than the anchor stirrer in the bottom areas of the tank. So, the new mixer has a better performance for mixing solid materials that have the possibility of sedimentation. At distances farther from the bottom of the tank, the tank with the anchor stirrer has better mixing than the new stirrer, and in these areas the anchor stirrer has a higher speed than the new stirrer. At a height of y = 0.880 m meters of fluid is divided into four symmetrical jets and the rest of the fluid flows upwards and reaches the free surface , and the speed increases with the height until reaching the height y = 1.330 m , where the length of the vortices decreases and circulates from the impeller to the impeller shaft due to the pumping effect . The speed of the fluid flow in the tank that is stirred by the new propeller is much higher than that of the anchor propeller , so the mixing time with the new propeller is less than that of the anchor propeller.