Simulation Of Liquid-solid Two-phase Flow In A Stirred Tank

Stirred vessels and reactors have many advantages such as higher mass/heat transfer,higher liquid/solid throughput.Stirred vessels have wide applications in the chemical,biological,food and pharmaceutical industries.Reasonable understanding the hydrodynamic behavior is the key to design,operate and control over this equipment.For the liquid-solid stirred tank,the flow behavior of the particles in the tank can well reflect the mixing degree of the mixing process.In this paper,the numerical simulation method is used to study the particle flow behavior of three-dimensional liquid-solid stirred tank with baffles.It is a reference for future theoretical research and optimization design.Flow behavior of particles is simulated by means of two-fluid model combining with kinetic theory of granular flow in a liquid-solid stirred vessel with baffles.The Huilin-Gidaspow drag model is used to obtain interphase interaction of liquid and solids phases.The virtual mass force is considered in simulations.The moving reference frame is applied to the rotation of numerical domain.First the liquid-solid stirred tank with Newtonian fluid is stimulated.Simulations indicate the stirred vessel consists of three regions,they are blade circulation region,conical induced region and near-wall region.As an increasing of the impeller speed,the turbulence kinetic and solids phase velocity rise,and the particles fluctuation is intensified.Particle density has little effect on granular flow,but liquid viscosity has a great influence on particle movement.With the increase of liquid viscosity,turbulent kinetic energy and granular temperature increase,and the mixing degree of each part in the tank is close.Predictions are compared with experimental data measured by Pianko-Oprych et al.in a liquid-solid stirred vessel.This comparison shows that the present model can capture the liquid-solid flow in a liquid-solid stirred vessel.In this paper,the mixing process of shear thinning fluid and solid phase in a stirred tank was simulated.The consistency coefficient and flow index are changed.The simulation results show that symmetric lower concentration of cave area exist around the impeller in the stirred tank,while the outer region having lower fluid velocity become the stagnation zone.As the flow index increases,the axial velocity and turbulent kinetic energy of the particles increase,and the flow index has the opposite effect on the granular temperature above and below the impeller.As the consistency coefficient increases,the diameter of the cave area in the tank decreases.The particle velocity and turbulent kinetic energy of the particles increase.Also,the granular temperature increases and the mixing degree increases in the circulation and near-wall regions.Compared with the influence of flow index,the consistency coefficient has little effect on the turbulent kinetic energy.