Liquid distribution of tubular piezoelectric print head

A calculation model of droplet ejection process for tubular piezoelectric print heads was established according to its structural parameters. Appropriate boundary conditions were chosen based on driving characteristics of the print head. Then, the calculation principles of simulation software on free surface flow problem were introduced. By taking the mixed solution of ethylene glycol and water as an example, the droplet formation processes were simulated. Pictures of droplets at different moments were obtained by a droplet imaging system and the correctness of the modeling and numerical algorithm was verified. Finally, the droplet formation processes of the print head for different input displacements, different viscosities and different surface tensions were simulated. The simulation shows that the liquid distribution performance is closely related to excitation displacement. With the surface tension fixed at 72.5 mN/m, the liquid with the viscosity of 4.0 mPa·s is difficult to be distributed by a 10 nm input displacement; however, that can be distributed into satellite droplets by a 15 nm input displacement. The results demonstrate that it is very important to find appropriate excitation conditions for liquid distribution. Droplets cannot be produced with too small excitation, while larger or many satellite droplets will be produced with bigger excitation. Increasing viscosity will postpone or restrain droplet formation while increasing surface tension can fasten droplet formation. The proposed calculating method in the paper has guiding significance on developing new print heads or studying the ejection capacities of print heads.