| As the key equipment in industrial production,the stirred tank has a wide range of applications in the petrochemical,food and biological fields.The stirred tank stirs the fluid through the rotation of the stirring blades,so that the materials in the stirred tank are evenly mixed with each other.However,the flow field generated in a stirred tank is generally a complex turbulent flow.Due to the lack of research on the mechanism of multiphase flow and turbulence,it is difficult to accurately describe the multiphase hydrodynamic behavior in the stirred tank,which limits the design and optimization of the stirred tank.Therefore,many difficult issues need to be further explored.In this thesis,the gas-liquid multiphase flow stirred tank in the process of preparing polyvinylidene fluoride by polymerization is taken as the research object,and a combination of numerical simulation and experimental verification is used to systematically study the hydrodynamic behavior in the stirred tank.In order to describe the hydrodynamic behavior of the gas phase and VDF phase in a stirred tank,the diffusion mechanism of the two in the stirred tank was studied.The numerical simulation method was used to measure the multiphase flow in the baffleless and baffled stirred tanks,and the axial velocity distribution,circulation velocity distribution,gas phase volume distribution,and VDF phase volume distribution were obtained under different blade inclination angles and different blade combinations.And other hydrodynamic parameters.Through comparison,it is found that?1?in terms of energy consumption:the power of the stirring tank decreases with the increase of the inclination angle;at the same inclination angle,the energy consumption of the inclined blade to open the turbine blade is lower than that of the inclined blade disc turbine blade;the same Under the conditions,the energy consumption of the stirred tank without baffle is lower than that of the stirred tank with baffle.?2?In terms of speed distribution:when the inclination angle?=45°,the axial component of the speed is the largest;under the same conditions,the“effective axial speed”of the inclined blade opening turbine blade in the monitoring area has a wide distribution range,and there is no obvious near the hub Large area reflow.Due to the different blade structure of the inclined blade disc turbine blades,the"effective axial velocity"distribution in the monitoring area is narrow,and a large area of backflow occurs near the hub.After adding a baffle in the stirred tank,the axial component of the speed is significantly enhanced.?3?In terms of mixed diffusion:the diffusion effect of the gas phase and VDF phase in the stirred tank is closely related to the size and distribution of"effective axial velocity".From the above aspects,it is concluded that the two structures of inclined blade opening turbine blade+propelling blade and double-layer propelling blade with an inclination angle?=45°perform better in various parameters.In order to further obtain the optimal solution,the mixing time T0.95.95 of the two rotor structures with and without baffle was compared.It was found that the mixing time was greatly reduced after the baffle was added.It reached 52.2%and 22.4%.The SST k-?DDES turbulence model was used to numerically simulation the stirred tank with two blades:the inclined blade opening turbine blade+propeller blade and the double-layer propeller blade with a baffle down tilt angle?=45°.After comparing the shearing effects in the flow,it is found that the shear deformation of the former is larger than that of the latter,so the product particle size is smaller.In order to verify the reliability of the numerical simulation,a batch of PVDF was produced experimentally for the two models,and the particle size and sphericity of the resulting products were observed under an electron microscope.By comparison,it is found that the former has a small particle diameter and high sphericity,which is consistent with the numerical simulation results. |
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