Effect of Impeller Type and Rotational Speed on Flow Behavior in Fully Baffled Mixing Tank.

Abstract

This paper reports the results of numerical study undertaken to investigate the effect of different impeller types and rotational speed on velocity field in mixing tank. The hydrodynamic of the flow in standard mixing tank generated by two impellers, Chemineer S-4 impeller (radial flow), Pitched Blade impeller (axial flow) is studied. Using ANSYS FLUENT v15.4. is used to solve the continuity and momentum equations incorporating the RNG K-ε turbulence model with the standard wall function available in Fluent. The multiple frames of reference (MFR) model is used for impeller modeling. The results show that the mixing performance of Chemineer impeller is better than the Pitched blade impeller at the same level of rotation speed. …………………………………………………………………………………………………….... IntroductionMixing tank is one of the techniques that used and play a significant role in industrial processes to homogenize the mixture of two or more fluids/solids by using rotating impeller. The better understanding of the fluids behavior in mixing vessel may improve the performance of impeller and the mixing process. The main aims of using mixing are to improve the mass and heat transfer and to generate a homogenized mixture to minimize the settling of the particles at the bottom of the tank. A summary of some recent published works in the literature is given below. Two models were used to determine the dissipation rate and its distribution in mixing vessel. Three dimensional simulations using the commercial CFD code FLENT 6.2.16 based on the Unsteady Reynolds Averaged NaiverStokes equations (URANS) model and Large Eddy simulation (LES) model was used.

Effect of Impeller’s Blade Number on The Performance of Mixing Flow in Stirred Tank using CFD Simulation Method

“…The present results were validated with the previous study as shown in Figure 6. Figure 6, showed that the present study is in good agreement with the Rasool et al, [4] specifically at position of 0.01, 0.2 and 0.3 as the errors were below 15%. However, the present results showed a significant deviated value with Rasool et al, [4] at the position of 0.2m as the error was high which is 32%.…”

“…Figure 6, showed that the present study is in good agreement with the Rasool et al, [4] specifically at position of 0.01, 0.2 and 0.3 as the errors were below 15%. However, the present results showed a significant deviated value with Rasool et al, [4] at the position of 0.2m as the error was high which is 32%. The deviation seems to cause by the variation in the usage of turbulence model.…”

“…The present study investigated the system in a stirred tank which was equipped with three types of impellers. The stirred tank design was based on the developed model from the previous research by Rasool et al, [4] as shown in Table 1. The system consists of a cylindrical vessel with a flat bottom and a diameter (Dt = 0.3 m) equal to the liquid's height (H=Dt).…”

“…This fluid motion somewhat created a circular mixing zone (eddy) region in which occurred around certain location positioned in the middle of the tank from the base surface. The middle circular motion also significant at almost half of the clearance between the impeller and the tank's bottom [4]. Rasool et al, [4] reported that the high mixing zone shrinks, notably in the tank's centre which caused the velocity in the middle region of the tank become lower.…”

“…In mixing systems, the hydrodynamic generated by the impeller has a significant impact on the ultimate product quality [3]. The primary goals of mixing are to increase mass and heat transmission, as well as to create a homogenized mixture to reduce particle settling at the tank's bottom [4].…”