为探究同轴气流对压电式微滴喷射过程的影响，自行设计并制造了设有同轴气流喷射槽的压电式微滴喷头，构建了微滴喷射与观测系统.采用双极性梯形波作为压电驱动波形，利用微滴喷射过程的可重复性，应用电荷耦合器件相机获取不同时刻的微滴图像；在此基础上，对同轴气流作用下压电驱动式微滴喷射行为进行了研究.结果发现：随着同轴气流强度的增大，微滴的延伸长度增加，其在喷嘴出口处的断裂时刻不受影响，在飞行过程中头部与尾部发生断裂的时刻延后；飞行微滴总体积略有减小，主液滴体积减小，而卫星液滴体积增大；主液滴与卫星液滴的前端速度和末端速度均有增大趋势，主液滴和卫星液滴末端速度的波动幅度与频率均有所下降；主液滴与卫星液滴形状都更趋于扁平，主液滴当量直径减小，而卫星液滴的当量直径则增大.研究阐明了压力波与同轴气流共同作用下微滴的喷射行为，揭示了同轴气流在微滴延伸、断裂和飞行过程中的作用规律，为同轴气流辅助式压电微滴喷头的设计提供了基础.
The aim of this study is to investigate the effects of coaxial airflow on micro-droplet ejection process. A coaxial airflow assisted piezoelectric printhead is designed and fabricated, and a micro-droplet ejection and observation system is constructed. A bipolar trapezoidal wave is adopted as the waveform of driving signal, and droplet images at different time are obtained by a CCD camera. Then the behavior of piezoelectric micro-droplet ejection based on the reproducibility of the droplet ejection process is studied. The results have shown that with the increase of coaxial airflow intensity, the liquid ligament length increases without the change of time for its breakup at the nozzle exit, while the breakup time of its head and tail is delayed. Meanwhile, the volume of a liquid drop ejected decreases slightly followed by a decreased primary droplet and an increased satellite droplet. Velocities of the leading and trailing ends of both the primary and satellite droplets tend to increase. The velocity fluctuations of the trailing ends of both the primary and satellite droplets are both decreased in amplitude and frequency. And a higher airflow pressure also leads to flattened shapes of the primary and satellite droplets, decreased equivalent diameters of the former, and increased ones of the latter. The study elucidates the behavior of micro-droplet ejection driven by a combination of the pressure wave and the coaxial airflow, reveals the mechanism of coaxial airflow in the process of extension, breakup and flight of micro-droplets, and provides the basis for design of coaxial airflow assisted piezoelectric printhead.
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