CFD Research On Solid-liquid Suspension In Non-baffle Stirred Tank With Multi-layer Pitched-blade Turbine

Solid-liquid suspension stirring is widely used in chemical production.The stirring speed,impeller diameter,impeller spacing,and impeller discharge flow direction have a great influence on the solid phase suspension quality.Therefore,in the case of considering power consumption,it is very important to select the appropriate operating parameters and structural parameters of the stirred tank.In this paper,the numerical simulation method was used to study the fluid flow in the no-baffled multilayer pitched blade turbine stirred tank.The influences of stirring speed,impeller diameter,impeller spacing,and impeller discharge direction on the free surface vortex height,turbulent kinetic energy distribution,power consumption,and solid suspension uniformity were investigated.The VOF method was used to study the gas-liquid two-phase motion in the stirred tank without baffle,and it was revealed that the flow field in the tank was closer to solid body rotation,and the fluid tangential velocity was an order of magnitude larger than the axial and radial velocity.The vortex depth increases with the increase in speed and impeller diameter.By changing the direction of the discharge flow of each layer of the blades,the tangential movement of the fluid in the tank can be broken and the vortex generation can be suppressed.When the discharge direction of the impellers is combined as U-U-D,the vortex depth value is the smallest.The relationship of the power consumption with the stirring speed and the diameter of the impeller is:P∝N2.74D3.89 in three downward Pitched-blade turbine(PBT)agitation system;and the power number of single PBT in non-baffle stirred tank is 0.174.Using the Euler-Euler model to study the gas-liquid-solid three-phase in the stirred tank,it is uncovered that the solid phase is subjected to centrifugal force and accumulates at the bottom of the tank and near the wall of the tank,and the solid volume fraction in the area near the stirring shaft is low.By increasing stirring speed,impeller diameter,and impeller spacing,the deposition area at the bottom of the tank can be reduced to a certain extent and the suspension quality can be improved.The mass of solid suspension decreases with the increase of impeller spacing.Combined with power consumption,it is determined that when the diameter of the stirred tank is 384mm,the optimum speed was determined to be 244rpm with impeller diameter 0.5T and impeller spacing 0.55T.Under the condition of D-U-D discharge direction combination,the solid deposition in the bottom of the tank is less,and the solid phase distribution near the stirring shaft,the middle and lower blades is good,and the overall solid suspension quality is the best.