Design Of Logarithmic Helicoidal Impeller And Research On Solid-Liquid Agitated Flow Field

With the development of industrialization and urbanization, the discharge of urban sewage increases substantially. The mixer, thought as a major sewage treatment equipment, is very important to the sewage treatment, which has obvious influence on the mixing and pushing effect. But there are some problems on the design of the impellers such as worse hydraulic model, lower efficiency and higher consumption of energy. With the development of the Computational Fluid Dynamics (CFD) and the measurement technologies, many researchers pay more attentions on the design and analysis of the new impellers. In this thesis, by analyzing the design of the impeller and the characteristics of the agitated flow field, a new type of the logarithmic helicoidal impeller was designed, and the study of the solid-liquid agitated flow field were also carried out by PIV. The main work and the achievements are as follows:1. The flow phenomena in the agitated tank were thoroughly analyzed based on the analysis of the design and the study on the development of the agitated flow field, and also combined with the theories of solid-liquid interaction flows, properties of agitated mixing and solids suspension, the main flow phenomena in the agitated tank were thoroughly analyzed. The numerical simulation models and computational methods for3D viscous turbulent flow in the tank were discussed.2. With the guidance of the theories of solid-liquid interaction flows, the design of the logarithmic helicodal impeller was firstly put forward in this thesis. This structure of the logarithmic hedicodal is good at reducing the hydraulic losses and resolving those problems, such as higher consumption of energy and lower efficiency. There are two parts in this impeller, one is the axial diversion and the other is the radial mixing. Both the axial and radial flow can be obtained without the reflection of tank wall. The impeller has higher efficiency and better mixing effect. According to the design experience of the solid-liquid centrifugal pump, the logarithmic spiral was taken to design the impellers.3. Based on the kinetic theory of granular flow, the basic control equations of the E-E model were established. As there were some different opinions about the particle viscous force, solid pressure force and fluid-patricle and particle-particle interactions, a new interaction force, which is an additional force, was leaded into the E-E model. And the Eulerian two-phase model was simplified by the above consideration. Based on the solid-liquid two phase model, the user-defined function was written, and the numerical simulation was carried out by FLUENT. The calculation results were compared with the experimental data or the other numerical results available in literature, which was found to have good agreements between each other. So, the hydrodynamics model established was good enough to predict the features of the solid-liquid flow. The concentration of solid particles, flow field distribution, and suspension effect were simulated accurately.4. The moments of the logarithmic helicoidal impeller under the different Re number were monitored during the numerical simulation by FLUENT. Then, the Power number and the Power were calculated, and the Np-Re curve was drawn. By comparing the result of different impellers under the same working conditions, the MK was lower in consumption of energy than that of PY, and the logarithmic helicoidal impeller was the lowest.5. The solid-liquid suspension flow generated by logarithmic helicoidal impeller in the square sewage tank was simulated and measured. The velocity, concentration, suspension, critical speed, consumption of energy and the mixing time of this kind impeller was compared with which in PY and MK impellers. The results indicated that:(1) The water was jetted in radial with the help of the logarithmic helicoidal impeller impeller. And the axial circulation flow was formed by guid of cyclic pats.(2) For a wide range of mixing speeds, the concentration of sludge particles is always lower in the upper location to impeller than in the lower position. As the rotation speed of the impeller increases, the sludge particles distribution in the flow field becomes uniform.(3) With the increase of rotation speed, the consumption of the power raises gradually, the uniformity of solid particle distribution decreases and the mixing time reduces. By means of the degree of uniformity in the suspension, the critical speed can be determined for those impellers.(4) For the mixing impellers (MK, logarithmic helicodal and PY) with same diameters under various rotation speeds, the PY impeller gives the best mixing result and MK impeller is the poorest. In addition, the PY impeller requires the highest power consumption, while the logarithmic helicodal impeller saves the most.6. The PIV measurement and the solid-liquid suspension experiments on the square sink were first performed in several methods. The experimental results show that the logarithmic helicoidal impeller and the MK generated axial single circulation flow, and the PY generated the double circulation flow. With the same diameter and speed, the PY was the fastest on the concentration distribution. But the deposition and the energy consumption were biggest. As the increasing of rotation speed, the uniformity of suspended solid was improved, but the energy loss was too big. So the logarithmic helicoidal impeller was better on effect and energy consumption.