Study On Formation Mechanism Of Main Droplets And Elimination Method Of Satellite Droplets In Liquid Jet

The droplet formation in liquid jet process which is a common phenomenon in nature,which is widely used in the production process of medicine,industry and agriculture.There are often small satellite droplets in the main droplet formation process.In some fields(such as the production of traditional Chinese medicine pills),too many satellite droplets not only waste resources but also affect the normal operation of production system.Therefore,it is necessary to study the formation of main droplets and the elimination of satellite droplets in liquid jet process.In this paper,the formation mechanism of main droplets in liquid jet process is studied by means of numerical simulation and experiment,and the effects of inner diameter of dropper,height of liquid surface,viscosity,surface tension,density,inlet velocity and frequency of external disturbance on the formation of the main droplet is revealed.The satellite droplets are eliminated by longitudinal disturbance.The optimal frequency and regularity of eliminating satellite droplets are explored.The results show that the wall thickness of the dropper has an important effect on the formation of the main droplets,and there is a critical value(0.687 mm)for effect of wall thickness on the main droplets.When the wall thickness of the dropper is less than the critical value,the main droplet volume,fracture time and fracture length of the main droplets increase with the increase of wall thickness.When the wall thickness is greater than this critical value,the wall thickness of the dropper will have no effect on the formation of the droplets.In a certain range,the main droplet volume increases with the increase of inlet velocity,surface tension and inner diameter of dropper.However,the increase of density and viscosity has an opposite effect.The relation of the effect on main droplet volume: density >surface tension > inner diameter of dropper > inlet velocity > viscosity.The fracture length increases with the increase of inlet velocity,density,viscosity and inner diameter of dropper.However,the increase of surface tension has an opposite effect.The relation of the effect on fracture length: inner diameter of dropper > surface tension > inlet velocity > viscosity >density.The generation period increases with the increase of surface tension.However,the increase of inlet velocity,density,viscosity and inner diameter of dropper has an opposite effect.The relation of effect on the generation period: inner diameter of dropper > density >surface tension > inlet velocity > viscosity.The satellite droplet volume increases with the increase of inlet velocity,density,viscosity and inner diameter of dropper.However,the increase of surface tension has an opposite effect.The relation of the effect on the satellite droplet volume: inner diameter of dropper > surface tension > viscosity > density > inlet velocity.By analyzing the flow line,the velocity field and the axial velocity of droplet formation process,it is found that the liquid velocity and pressure are the highest at the fracture of the necking line,and the liquid movement direction is opposite at the primary fracture and the secondary fracture.In the formation process of droplets,there is a vortex.The vortex makes the upper end of satellite droplets move down and the lower end move up,causing satellite droplets to oscillate in air.The longitudinal disturbance of appropriate frequency can eliminate satellite droplets in jet process.The eliminated optimal frequency of the satellite droplets is different in the different working conditions.The optimal frequency increases with the increase of the liquid surface height and the inner diameter of dropper.However,the optimal frequency decreases with the increase of the glycerol mass fraction.The longitudinal disturbance can reduce the main droplet diameters.At the same time,the disturbance basically eliminates the effect of the liquid surface height on the generation period of the main droplet,but the effect trend of other parameters on main droplet is similar to the previous research results.By studying the formation mechanism of the main droplets and the elimination method of the satellite droplets in the jet process,this paper provides a theoretical basis for the precise control of the droplets and the reduction of the satellite droplets in the actual industrial production,which plays a positive role in saving resources,environmental protection,reducing production and operation costs.