| Electrohydrodynamic Drop-on-demand Printing is a micro-nano droplet jet forming technology which is progressed constantly within the decades,considered as an important development direction for micro-nano 3D printing.Due to the extremely high requirements for droplet precision and generation frequency in micro-nano structure manufacturing process,how to jet high-resolution droplets stably at high frequency has always been a research focus in on-demand printing technology.However,the experimental research is affected by the short time(millisecond level)of the entire process of printing,the micro-nano scale,the difficulty in capturing the liquid level and other problems.The mechanism of various parameters on jet injection,fracture and meniscus oscillation behavior in the process of printing are still not clear.Therefore,this paper simulates the printing process on the strength of experimental results.The main work is as follows:(1)The numerical model of the printing process is set up by the open source program OpenFOAM.The finite volume method is used to discretize the N-S equation.The meniscus movement is captured by the VOF method.The surface tension treated as a kind of body force is calculated by the CSF method.The leakage dielectric model is chosed to calculated the electric field force.The whole printing process is simplified into a two-dimensional axisymmetric problem,which reduces the amount of calculation.(2)The printing process with a DC constant voltage is simulated.The effects of voltage,viscosity and conductivity on the various stages of the printing process and the shape of the Taylor cone are studied.Get the relationship between deformation time t_f,jet time t_j,rebound time t_r,Taylor cone angle and length and voltage,viscosity and conductivity.Deformation time t_f varies inversely with voltage and conductivity and depends linearly on viscosity.Jet time t_j is mainly affected by viscosity.Rebound time t_r goes up in proportion to viscosity and goes down with incremental conductivity and voltage.Taylor cone angle varies inversely with viscosity and is in proportion to conductivity and voltage.The length of Taylor cone alters in the contrary way to the angle.(3)The printing process with a DC pulse voltage is simulated.The relationship between deformation time t_f,jet time t_j,rebound time t_r,Taylor cone angle and length and voltage,viscosity and conductivity are derived when the pulse voltage frequency is 1000Hz,800Hz and 625Hz and the duty cycle is 50%.Under the action of pulse voltage,the printing process tends to be more sensitive to the frequency than other parameters.The deformation time t_f and jet time t_j decreases in inverse proportion to the voltage.The rebound time t_r has a proportionality with the voltage.The Taylor cone shape change is consistent with the change rule under a constant DC voltage.(4)The location and size change of the vortex during the jet process are simulated under the action of DC constant voltage and DC pulse voltage.In each printing process stage,the variation of the vortex's position and intensity can be got.It is found that the position and size of the vortex produce extreme values when the liquid line is generated and broken.Through numerical simulation,the effects of solution properties and voltage on the Taylor cone shape and characteristic time of each stage during the formation and injection of printing under constant DC voltage and pulse DC voltage are obtained and analyzed,which provided an effective way to analyze and reveal the mechanism of the injection and oscillation behavior of charged solution under electric field.The position and size of the internal vortex during the jet printing process were thoroughly investigated.And the action rules of various parameters on the flow field inside the meniscus are clarified,which is of great significance to further improve the stability of Drop-on-demand Printing. |
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