Research On The Mechanical Mixing Of Floating Particles With High Concentration In Viscous System

Mixing operation is widely used in many process industries such as oil, chemical engineering, food, medicine, metallurgy, dyestuff, papermaking and sewage treatment. It also plays an important role in homogenization, emulsification and fermentation. The solid-liquid mixing of floating particles, which is different from the solid-liquid mixing of sediment particles, aims to draw down the floating particles and then disperse the particles into stirred vessel. Much effort has been spent on the research of solid-liquid mixing of sediment particles, while only a little effort on the research of mixing of floating particles. There are few research results that can be used for the design of solid-liquid stirred vessel of floating particles. It had been proven infeasible to copy the solid-liquid stirred vessel design of sediment particles in the design of solid-liquid stirred vessel of floating particles. In this paper, the influences of the structure of solid-liquid stirred vessel and properties of the mixture on drawing down the floating particles were discussed based on the research of experiments and numerical simulation. Some relevant parameters, such as the just drawn down speed, power, flow field and concentration field, were obtained, which laid a good foundation for industrial application.hi order to obtain the optimum structure of solid-liquid stirred vessel of floating particles, the influences of impeller, submergence, ratio of diameter of impeller to diameter of the vessel and the baffle on the just drawn down speed and power were investigated in 75.3mPa-s viscous system. The results show that the just drawn down speed and power of upward-pumping impellers are larger than those of downward-pumping impellers. The optimum structure of solid-liquid stirred vessel of floating particles should be the vessel combined with downward-pumping marine propeller (S=0.25T) and one full baffle.With the optimum structure of solid-liquid stirred vessel, the influences of viscosity, solid concentration and size of floating particles were investigated. The results show that the just drawn down speed and power would increase with the increase of liquid viscosity, as well as the increase of solid concentration and particles size.Finally, the flow fields, concentration fields and distributions of turbulence intensity of three different impellers were investigated by the method of numerical simulation. The results of simulation using the Gidaspow drag model agree well with the experiment, which shows the drag model is suitable for the simulation of solid-liquid mixing of floating particles. The positions with the largest turbulence intensity in the surface of three different impellers are close to each other, which are also close to the position of the formation of eccentric vortex. The optimum ratio of diameter of impeller to diameter of the vessel of the downward-pumping marine propeller is 0.5. The mixing time differs at different monitoring positions, which is related to the speed of the flow.