Different from the general ultrasonic atomizer
operating at high frequency, the proposed one is driven at much lower
frequency but with larger amplitude. For this application purpose, a
simple structure constructed with a hollow tube encircled with
piezoelectric actuators is considered to use. Instead of using a
ring type of ceramics, three pieces of same size sectional-type of
d33 ceramic actuators are employed around the hollow tube with
equal distance to generate higher radial vibration. While the tube
fixed at both ends is vibrated with assigned vibration mode shape, a
suitable wave is formed to produce larger amplitude in need. The fluid
inside the tube will flow out smoothly from a very small hole
implemented on the largest amplitude of the waveform. Thereafter,
atomization occurs on the tube surface around the hole immediately
while enough oscillation frequency and amplitude is provided. With
such design structure, several cases with different tube length,
resonance frequency, vibration amplitude are investigated for
comparison. Particle size of 5~30μm and uniform spray distribution is
the target for an example of industry-used spray fluid with viscosity of
about 8~12cp. A measurement system is set up including high speed
camera, laser as a light source, and software Image J for estimation of
particle size and particle distribution. Water is used for experimental
testing in this study. While drives the hollow tube with operating
frequency of 45.3 kHz and the maximum amplitude is great than
6.8μm, atomization occurs with average particle diameter of 28.3μm
and good uniformity and distribution. However, increasing vibration
amplitude, on the contrary, the diameter of the particle becomes larger.
For example, while increases amplitude up to 9μm, atomization occurs
with average particle diameter of 34μm, and the uniformity and
distribution becomes worse. This interesting phenomenon may result
from large amplitude at enough vibration frequency easily makes
atomization occur but large amplitude engenders with large particle
diameter.
