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.

An experimental and numerical investigation is carried out for the heat transfer from a cube faces subjected to impinging jet which centrally strikes the top face of the cube. The cube is subjected also to a comparatively low velocity cross flow through the duct occupying the cube. Different factors affecting the cooling characteristics of the cube are studied as orifice size, jet velocity and orifice to cube top distance. The results show that cross flow increases heat rates from the cube for small size orifices and low impinging jet velocities. Orifice sizes equal or bigger than cube size will isolate the cube from cross flow effect especially at high impinging jet velocities.

The Characteristics of single and two- phase flow from a circular turbulent free jet from a nozzle of 10 mm diameter were investigated experimentally and numerically. The measurements were conducted for ReJ = 10007 - 31561. The velocity was measured at location from the nozzle y/D (0-8) in axial and radial directions. The two phase measurement were done by using natural construction sand as a solid phase of sizes (220,350,550) µm and loading ratios (mass flow ratio of sand to mass flow rate of air) in the range (0.18-1.38). Two phase air velocity of jet showed that the introducing of natural sand particles gives lower jet velocity attributed to momentum transfer to particles. The smaller particle size leads to lower values of velocity. The velocity found to be decreased with loading ratio increase. The numerical simulation was performed for single and two phase jet flow. RNG K-ε turbulence model was used to simulate the flow of fluid and the discrete phase model to simulate the particles flow. The results form numerical simulation showed a good agreement with experimental results.

An experimental data of flow field, pressure coefficient and heat transfer of a jet impinging normally on a flat target plate are presented. The measurements of temperatures and static pressures were carried out for flow from three orifices of 5, 10 and 20 mm diameter for orifice-to-target plate distances of 5, 10, 25, 50, 70, 100 and 120 mm from the orifice exit. The axial development of flow structure of the jet from the orifice was investigated by measuring the radial jet velocity distributions at the same axial distances used to measure heat transfer and static pressure. The results show that pressure coefficients distributions on the target plate are similar to the velocity distributions in the impinging jet which indicates the strong relationship between the two parameters. The pressure coefficients from large orifice diameter are higher than the values from the small orifice diameter for same orifice-to-target plate distance. The results also show a nonlinear increase of heat transfer rate with orifice size and the ratio of axial distance to orifice diameter (X/d). The nonlinear behaviour may be attributed to the complex nature of flow structure at the stagnation region. The high velocity gradients at the stagnation zone leads to higher turbulence and comparatively higher values of heat transfer rates for large orifice diameter.

Heat transfer between a heated flat plate and normal impinging gas‐solid two‐phase jet flow was investigated. A single jet from a nozzle of 10 mm diameter at nozzle‐to‐plate distance/nozzle diameter ratio in the range of 2–8 was used. Natural sand particles with average diameters of 220, 350, and 550 μm were used as a solid phase. The effects of particle size and loading ratio (mass of sand/mass of air) at different jet velocities on impingement cooling characteristics of the flat plate are investigated. The numerical simulations were performed with ANSYS Fluent 14.7 for a steady, three‐dimensional, incompressible turbulent flow using Eulerian simulation for the gas phase and Lagrangian simulation for sand particles. The experimental results show that the existence of sand particles decreases the Nusselt number compared to air jet flow. The single and two‐phase flow experimental results are close to predictions when the particle reflection option is used in the simulation. The discrepancy in local values near the stagnation point can be attributed to the complex nature of the two‐phase flow at the stagnation point that includes reflection of sand particles at different angles.