Generation of multi-stream uniform droplets based on piezoelectric excitation
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摘要:
针对基于压电激励的大质量流量多股射流均匀液滴生成问题，研究了压电激励频率和波形对液滴生成特性的影响规律，基于图像捕捉技术对射流图像进行处理，获得了液滴粒径大小、均匀性和射流断裂距离等统计数据。实验结果表明：在射流喷射速度一定时，激励频率增加引起射流破碎的特征波长减小，生成的液滴直径减小。除了基于射流不稳定理论预测的射流破碎最优激励频率之外，集液腔内液体共振也会影响射流破碎距离和液滴生成效果。在激励频率和电压幅值一定时，消耗能量最低的三角波激励获得的射流破碎距离最短、液滴生成效果最好，正弦波次之，而消耗能量最高的方波激励获得的效果最差，因此适用于单股射流的激励波形选择标准并不适用于多股射流的激励波形选择。
Abstract:For solving the uniform droplets generation problem of multi-stream jets based on piezoelectric excitation, the influences of piezoelectric excitation frequency and waveform on droplet generation characteristics were studied. The droplet diameter, uniformity and jet fragmentation distance were obtained by processing jet images based on image capture technology. The experiment results showed that when the jet velocity was fixed, the characteristic wavelength of the jet fragmentation and the droplet diameter decreased with the increment of excitation frequency. Apart from the optimal excitation frequency of jet fragmentation predicted by the jet instability theory, the liquid resonance in the cavity also affected the jet fragmentation distance and the droplet generation characteristic. With the same excitation frequency and voltage amplitude, the triangular wave with the lowest energy consumption had the shortest jet fragmentation distance and the most excellent droplet generation characteristics, followed by the sine wave. The square wave with the highest energy consumption had the worst droplet generation characteristics. Therefore, the criterion for selecting the exciting waveform of single-strand jet is not suitable for multi-stream jets.
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图 5 激励频率对无量纲射流直径的影响
Figure 5. Influence of excitation frequency on the dimensionless jet diameter
图 6 相机视场出口处液滴生成图像
Figure 6. Generation of droplets at the exit of camera field of view
表 1 实验工况
Table 1. Experimental conditions
工况 激励波形 激励区间/kHz 喷射速度/（m/s） GK-01～GK-11 方波 1.0～3.0 10.6 GK-12～GK-22 正弦波 1.0～3.0 10.6 GK-23～GK-33 三角波 1.0～3.0 10.2 
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表 2 射流断裂数量统计结果
Table 2. Statistical result of the number of fragmental jets
波形 频率/kHz 射流断裂数量 <30 cm 30～42 cm >42 cm 方波 1.2 0 0 16 2.2 0 0 16 正弦波 1.2 4 11 1 2.2 4 10 2 三角波 1.2 4 10 2 2.2 10 6 0
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表 3 射流断裂距离统计结果
Table 3. Statistical result of the length of fragmental jets
波形 频率/kHz 射流断裂距离/cm 平均值 标准差 正弦波 1.2 36.81 2.94 2.2 36.11 2.82 三角波 1.2 35.93 3.31 2.2 36.24 2.85
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