การวิเคราะห์ความสามารถในการผสมของถังกวนผสมโดยใช้พลศาสตร์ของไหลเชิงคำนวณ

Abstract

Mixing capability of the stirred tank reactor depend on fluid flow distribution and propertiesof particles. Understanding of flow characteristics within the tank is important in assessing the performance of the mixing process. This research studied and analyzed the motion characteristics of fluid and particles within a Stirred Tank Reactor ( STR) with 8-blades of Rushton turbines using Computational Fluid Dynamics (CFD). Large Eddy Simulation (LES) are applied to capture the turbulence and the sliding mesh technique ( SM) to simulate the impeller motion. The results at rotational speed 100, 200, and 300 rpm, it shows that the centrifugal force is responsible for generating a flow that flows from the tip of the propeller in the radial velocity. For the Coriolis force occurs after the fluid moves. The Coriolis force which presents after fluid start moving, can be separated into radial and tangential direction. The horizontal motion of fluid change into vertical direction (axial-plane) at the wall of reactor. This fluid distribution creates a mixing characteristic with in the tank. At the mixing continues, the mixing capability decreases because of flow field becomes steady or called bulking motion. The particle motion characterization was observed using the Multiphase Particle-in-Cell ( MP-PIC) method to calculate the movement of 625, 1,250, and 2,500 particles respectively. The particle studies were done on two the rotational speed, those are, 100 and 200 rpm. Particle distribution and mixing efficiency were analyzed by two different schemes: (1) the principle of distribution of all particles on a plane and (2) the principle of the ideal particle distribution on the plane. The initial mixing state, all particles on plane schemes shows higher mixing efficiency then ideal particles on a plane schemes. Both schemes present similar trend of mixing efficiency with time. The mixing efficiency of rotational speed 100 rpm is less than 200 rpm.