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5.5. The custom made vibrating orifice drop generator. The main body
had a hydraulic plug-connector (RiB 01 04 10 CV, Landefeld, Germany)
for the liquid feed, a BNC connector for the excitation signal,
and a thin slot for the piezoceramics buzzer. The cap contained the
pinhole and sealing ring out of rubber. The CAD image shows the
interior liquid passage for water jet and purging. The buzzer accepts
5 V TTL signal, and thus can be directly controlled by the NI 6602
module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
5.6. The monodisperse drop train was created with a 100 µm pinhole and
a 20 kHz excitation signal. The drop had an equivalent diameter of
199 µm and a downward velocity of 10.4m/s. The four images were
taken at 6 mm, 9 mm, 10.5 mm and 18 mm downstream from the
outlet of the drop generator. The disturbance wave had a roughly sinusoidal
shape at early stages. Approaching the disintegration point,
the perturbation wave became composed of a thin strip and a plump
bulge, which resulted in periodical generation of a major drop and a
satellite drop one after another. Both the major drop and the satellite
oscillated along the vertical path, and generally merged with
each other regularly, forming a stable drop train. . . . . . . . . . . . . 133
5.7. The monodisperse drop train was created with a 25 µm pinhole and
a 30 kHz excitation signal. The drop had an average diameter of
87 µm and a downward velocity of 9.3m/s. The five images were
taken at 1 mm, 1.5 mm, 4 mm, 9 mm and 11.4 mm downstream
from the outlet of the drop generator. The deformation of the liquid
jet, the formation of two drops by one perturbation wave, and
the first merging of the drops was the same as with 100 µm pinhole.
The peculiarity with 25 µm pinhole was the secondary merging: the
major drops collided with each other regularly, and formed a stable
drop train of larger drops. . . . . . . . . . . . . . . . . . . . . . . . . . . 134
5.8. Frequencies of the perturbation wave, the jet breakup and stable
drops of the drop train generated with the 50 µm and 100 µm pinholes.
The liquid jet speeds were between 7.3m/s and 8.3m/s. The
speed of stable drop was approximately 1m/s slower than the jet
speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
250 List of Figures