圆管式压电喷头的液体分配

Liquid distribution of tubular piezoelectric print head

针对用于喷墨打印的圆管式压电喷头建立了计算模型,并且根据它的驱动特点选择了合适的边界条件。介绍了仿真软件针对自由表面流动问题的计算原理。然后,以乙二醇水溶液为例,计算了压电喷头分配该溶液的分配过程;利用液滴成像系统获取了不同时刻的液滴图像,验证了建立的模型和数值算法的正确性。最后,计算了压电喷头在不同输入位移、不同黏度以及不同表面张力下的液体分配过程。仿真结果显示:液体分配性能与激励位移密切相关,在72.5mN/m的表面张力作用下,10nm的输入位移很难分配黏度为4.0mPa·s的液体,而15nm的输入位移在分配黏度为4.0mPa·s液体时却能够产生卫星液滴。因此,对于某种液体寻找一个合适的激励条件非常重要,过小的激励产生不了液滴,过大的激励则会产生较大甚至多个卫星液滴;增大黏度会延缓或阻滞液滴形成过程,增大表面张力却能加快液滴形成过程。本文的计算方法对于研制新式喷头或者研究喷头的喷射能力均具有指导意义。

A calculation model of droplet ejection process for tubular piezoelectric print heads was es- tablished 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 mo- ments 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 dis- tributed 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 excita- tion conditions for liquid distribution. Droplets cannot be produced with too small excitation, whilelarger 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.