Numerical Simulation And Physics Of Two-Phase Flow Behavior In Gas-Liquid Stirred Tank

The stirred tank metallurgical engineering,petrochemical,water treatment,biopharmaceutical and food processing as key equipment in industrial production.The stirred tank mainly through the mechanical movement of the fluid to stir,so that the contents of the kettle mix well with each other.However,the flow field generated by the stirred tank is generally a turbulent form of random turbulence.Due to the lack of the mechanism of multiphase turbulence,the thermodynamic behavior of multiphase fluid in the stirred tank is difficult to describe accurately,thus limiting the design and optimization of stirred tank.Numerous challenging fields of the problem still need further exploration.In this paper,the hydrodynamic behavior in stirred tank which uses to treat cyanide-containing wastewater was investigated in experimental measurement and numerical simulation.In order to describe the behavior of the gas phase in the turbulent flow field,the mechanism of the breakup and coalescence of the fluid particle is studied,and the fluid particle behavior models are further incorporated into the coupling model to calculate the bubble size distribution.The two-phase flow of eccentric and non-eccentric stirred tank was measured by probing and dynamic photographic methods.The hydrodynamic parameters such as gas holdup,bubble size and bubble velocity were obtained by different eccentricity.The above data cannot only describe the basic distribution of the gas phase in the stirred tank,but also can be utilized as an important basis for the comparison of the simulation results and the CFD-PBM coupling calibration.The flow field of the stirred tank was systematically studied by numerical simulation.Through the calculation of the flow field,the double-layer impeller can overcome the inhomogeneity of the liquid velocity distribution and the "dead zone"phenomenon in single-layer stirred tank.For mitigating surface fluctuation,adding baffle effect is preferable to change eccentricity.The calculation results also show that When the medicine feeding port is set at a distance of 8 cm from the center of the stirred tank,the number of feed ports is more than four annular distributions,and at the critical speed of about 30 rad/s?40 rad/s.the mixing efficiency of the medicament can be optimized.Based on the study of the two-phase distribution in the stirred tank,it is proposed to adjust the operation of the two-phase distribution of the stirred tank,and obtain the virtual mass force which is difficult to be measured by the experiment to obtain the motion between the two phases.Based on the theory of eddy current and turbulence,the mechanism of the breaking process of the flowmeter under turbulence is studied.In order to reasonably describe the bubble crushing process,not only the flow rate of the granule collision is corrected,but also the influence of the energy constraint condition and the pressure constraint condition on the bubble breaking criterion are considered.The range of turbulent vorticity is 21.4?????5d0,and the critical particle size is obtained by the model calculation.Due to the different physical properties,the particle size distribution of the air-water system is "M" shape,and the particle size distribution of the oil-water system is "?" shape.In the study of the droplet coalescence process,the relevant drainage model and the flow contact model were established respectively.In the establishment of the drainage model,the outer membrane and liquid membrane internal two parts were discussed,respectively.And then employ the energy conservation principle,force analysis,access to contact model.The influence of turbulence and two-phase physical properties on the rate of coalescence is analyzed from the mechanism.Using the Population Balance Model,the breakup and coalescence models were incorporated into the framework of the multiphase flow calculation,and then the CFD-PBM coupling model was established.The bubble size distribution of the stirred tank was systematically predicted and analyzed.The numerical simulation results demonstrate that the bubble behavior in the effluent zone is mainly broken,and the bubble behavior in the upper circulation zone is mainly dominated by aggregation,while the gas phase is mainly transported in the lower circulation zone.In addition,in view of the large specific surface area required for the gas phase of the aeration process,this paper proposes increasing the rotational speed and reduce the ventilation,and utilized the annular distributor to reduce the bubble size.Moreover,considering the effects of power,service life and mixing capacity a better aeration effect is obtained at a critical speed of 35 rad/s.