Experimental And Numerical Study On Fluiddynamics And Mixing Process In Stirried Tank

Mixing equipments are widely used in many industry processes. Althouth there are lots of theoretical and experimental study, the study of mixing and the design methods are not developed well up to now. The semi-empirical methods are still the main tools for design and scale-up industry processes. To meet the purpose for optimal design, scale-up and fully understand the processes occurring in agitated equipments, there are need for careful experimental measurements and mathematical models to measure and describe the characteristics of flow in such equipments. The combined method of using Laser Doppler Velocimetry (LDV) and Computational Fluid Dynamics (CFD) for the study of flow and mixing characteristics in stirred tank is carried out more and more frequently.In this study, based on the function provised by the commercial CFD code (CFX), three-dimensional flow fields in stirred tank are carefully studied, including the influence of impeller models, turbulent models, grid density and difference scheme to the computational results. The influence of such factors on velocity distribution near the impeller mainly focuses on the maxium radial and tangential velocity. It is found that the results using sliding grid, RNG k- e turbulent model and high-density grid are in good agreement with experimental data. While for difference scheme, the results of second-order upwind are better than that of QUICK. For turbulent kinetic energy, all kinds of calculation are under-predicted. With high-density grid and high order difference scheme, such as QUICK, the computation can get better results. Although RNG k- ?turbulent model is good for velocity distribution, its results of turbulent kinectic energy is worse than the standard k- ?model.The turbulent flow fields of Newtonian (water) and Non-newtonian (CMC water solution) fluids have been measured by using Laser Doppler Velocimetry. The research includes the influence of impeller diameter, concentration of CMC solution and interlayerspacing of dual impeller to the flow field. The experimental results show that the two different fluids have the same flow form under turbulence. The main difference is that the velocity of CMC solution is weakened because of high viscosity. The velocity distribution near the impeller, with high axial velocity and low radial velocity, is the same as ring jet flow. The flow form of dual impeller and the velocity distribution near the impeller depend highly on the interlayer spacing.According to the experimental research, the commercial CFD code (FLUENT) is used to simulate the turbulent non-Newtonian fluid flow in single and dual impeller stirred tank systems, and the results are compared with LDV measurements made in this dissertation. The predicted results are in good agreement with experimental research for single impeller flow field, and the lower concentration of CMC solution, the better of the predicted results. For velocity distribution of dual impeller systems, there is still deviation between the predicted and experimental results, especially for the predicted radial velocity.Program for mixing calculation was developed based on the commercial CFD code (CFX). It was used in the numerical study of mixing process in single and dual Rushton turbine stirred tank systems. Coupled and segregated solution of momentum and mass equation were adopted. The calculated concentration response curve is consistent with the literature data. Both methods predict the same change rule of mixing time. But the value of mixing time from coupled solution is lower than that from segregated one. Coupled solution needs much more computational efforts than the segregated. It has shown that mixing process depends on the flow field used for mixing calculation. The value of mixing time also depends on detecting and feeding location. When the tracer is fed near the impeller, the mixing time is the lowest. While it is fed near the bottom of the tank, the mixing time is the largest. For dual impeller stirred tank system, when the flow generated by the two impellers has...