fluid flow in mixing tank, mixing, Retreat Curve impeller This paper reports the results of numerical study undertaken to investigate the effect of impeller rotational speed on velocity field in mixing tank. The hydrodynamic of the flow in standard mixing tank generated by retreat curve 3-blaed impellers, (radial flow) is studied. Using ANSYS FLUENT v15.4.to solve the continuity and momentum equations incorporating the RNG K-ε turbulence model with the standard wall function available in

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... The multiple frames of reference (MFR) model is used for impeller modeling. The results show that the velocity fluctuated increased with the rotational speed. Copy Right, IJAR, 2017,. All rights reserved. ...................................................................................................................... Introduction:- Mixing tanks is one of the techniques that is widely 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. Means e.g. the main aims of using missing is 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. (Wei et al 1997) [1] Studied the influence of the number and width of baffles in mechanically mixing vessel with and without aeration on the fluid hydrodynamics and mixing tank. (Ducoste and Clark 1999) [2] Employed the Computational Fluid Dynamics (FIDAP) code called Fluid Dynamics International, Evanston, IL in the study. The model was a simple geometry consists of the submerged impellers in cubical mixing vessel. The k-ε model was used to simulate the turbulence and the flow pattern induced in the vessel. (Masoud Rahimi 2005) [3] Used CFD simulation to study the influence of impellers number and layout on mixing time. A large storage tank of 19000m3 contain three types of crude oil with difference density. (Aoyi et al 2008) [4] Investigated the hydrodynamics of fluid in mixing stirred vessel agitated by Rushton turbine with low clearance condition. The CFD technique and LDV measurements were performed in order to understand the flow pattern and estimated the mixing time. (Angelique Delafosse et. al. 2008) [5] Investigated the hydrodynamics in mixing tank by CFD simulation. 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 Naiver-Stokes equations (URANS) model and Large Eddy simulation (LES) model was used (Zadghaffari et. al. 2008) [6] Studied the flow field, power and mixing time in mixing tank agitated by a double Rushton turbine. It was observed that a considerable reduction in mixing time can be achieved by increasing impeller rotation speed and reasonable agreement between the simulation and experimental results were obtained. The comparisons pointed the advantages Corresponding Author:-Adnan A. Abdul rasool. Address:-A: mech. Eng. Dept, college of engineering, al-mustansiriya university, Baghdad, Iraq.