Dynamics Of Drop Formation And Transition From Dripping To Jetting In The Presence Of An Electric Field

An investigation on geometric and dynamic characteristics of droplet in stagnant air was carried out.Based on the study of the droplet formation process,this article measures the shape,size,and movement trajectory of the droplets by experimental methods.The growth,stretching and separation of droplets are also explored.Meanwhile,three different regimes including periodic dripping,dripping faucet(chaotic dripping)and jetting are explained in detail,as well as the effect of electric field on the transition from dropping to jetting.In the process of research,the liquid was ejected from the orifice of the vertical capillary tube at a certain flow rate through the syringe pump.By establishing a visual experimental platform,the formation process and dynamic characteristics of droplets are observed,recorded and analyzed.The main work and conclusions are as follows:1.In the absence of an external electric field,an experimental research was conducted on the morphology and dynamics of dripping or jetting.Using high-speed digital cameras,the time evolution of the three regimes was recorded.With the flow rate(We)increases,the periodic dripping,dripping faucet and jetting of the Deionized water(DI)and Anhydrous ethanol can be clearly observed.In the periodic dripping,the dimensionless length of the Deionized water gradually increases with oscillation,while the dimensionless length of Anhydrous ethanol shows slightly oscillation during the continuous increase.In the dripping faucet,the size of the primary droplet is no longer constant,and the Deionized water has an irregular oscillation frequency.The variation of the dimensionless limit length and width of the main droplet with the flow rate and the capillary tubes diameter is discussed.A qualitative prediction of the diameter of the droplet is made by formula.2.In the presence of an external electric field,the dynamics of the droplet and the oscillation of the charged meniscus at low flow rates are studied.At the moment of droplet separation,the critical size of the main droplet and the liquid filament is used to characterize the dynamics of droplet formation and meniscus oscillation.The results show that the diameter of the main droplet decreases with the increase of the voltage(Bo _E)and is related to the diameter of the capillary tubes.Meanwhile,the limiting length of the droplet decreases,while the diameter and length of the liquid filament increase with the increase of Bo _E.When the primary droplet separates,the meniscus usually oscillates.The oscillation frequency increases with the increase of Bo _E and is greatly affected by the flow rate.At the same time,a formula for predicting the oscillation frequency of a charged meniscus is proposed.By the qualitative analysis of the change of the oscillation frequency,it is in good agreement with the experimental value.Its amplitude(or displacement)is greatly affected by the voltage(Bo _E)and increases with the increase of the voltage(Bo _E).3.In this paper,the transition of liquid from dripping to jetting in the presence of an electric field,and the necking process of drop formation in the dripping regime are explored.It is clearly indicated that the voltage(Bo _E)has little effect on the necking process in the dripping regime.Due to the stabilizing effect of the increase of the electrical shear stress on the gas-liquid interface,the critical values(We_c)of transition from dripping to jetting is advanced,that is,the flow rate(or We_c)corresponding to the second critical velocity V_J decreases.By establishing the necking model and the transition model of the droplet,the criterion is got for the transition from dripping to jetting in the presence of an electric field.When the drop formation in the form of dripping faucet,the transition from dripping faucet to jetting regime occurs as the electric potential(Bo _E)increases,where a sudden transition could be observed in a certain range of liquid flow rate.