Numerical Simulation And Optimization Of Static Mixers

In this dissertation, coagulant mixing process in static mixer was studied and analyzed. The numerical simulation method was used to investigate the performance of static mixer with rows of long tabs verified by experimental data and a new internal structure in mixing process, the influence of changes in static mixer with rows of long tabs.Grid partition was an important step of numerical simulation. Internal structure of static mixer with rows of long tabs was complex, so it was divided into several parts and made grid partition respectively. The grids near the wall were made more compact. At last the number of grid was 405567. The flow process was unsteady and second-order implicit was used for time discretion. The k-εmodel and species transport models was established to research this project. The velocity field, velocity vector field and turbulent kinetic energy distribution were analyzed, the changes of which were identical with theoretical analysis. The result showed that tabs made part of fluid flow to the axis,which promoted the mixing effect. The second phase distribution was got and the COV value was used characterizing the mixing effect. The COV of xoy surface was calculated, which was agree with the experimental data of literature 31.The agreement of numerical simulation and experimental results proved that numerical simulation was a kind of effective method, the selection of turbulent models and mixing models is appropriate. Base on the study and optimization,the static mixer with long tabs,vertical inflow and deflection 30 degrees was optimized. The angle between tabs and cross section was changed and they were 15°,30° and 45°. The spacing between tabs and the wall was small, so unstructured grids was used. Flow field showed the three new stuctures made the fluid emerge circular motion and the original model(0°)did not, which could improve the mixing effect.The result showed COV decreased firstly and then increased and the pressure loss constantly decreased with the increasing of the angle. Considering the mixing effect and pressure loss comprehensively, the structure with 30°have the best performance.The position of mixing components was put periodically and unparallelly, which can improve the mixing effect greatly. A new structure, Spiral belt static mixer with changing diameter was studied. Spiral belt was fixed with wall through large diameter part.The target of it gave the disturbance at different places. Then the mixing effect was compared with that of static mixer with rows of tabs. The result showed that spiral belt static mixer with changing diameter promoted the mixing effect greatly and the COV of it was less than 0.05. The mixing effect relative to static mixer with rows of tabs increased 10 times and the pressure loss only increased 3 times.