Theory Research And Application Of Ultrasonic Dry Cleaning Technology

Ultrasonic dry cleaning technology is a new type of dry cleaning technology,which clears away fine particles of dust adhering to a surface by the combination of high-speed airflow and ultrasonic wave.This system does not require additional cooling or drying processes.Moreover it does not need high cost consumables such as highly pure gases or chemical solvents.In this paper,the resuspension of particles adhering to the surface in ultrasonic dry cleaning area and the mechanism of flow induced cavity oscillation in the air flow channel with variable cross-section of ultrasonic cleaner were discussed.The research provided a theoretical basis for the prediction and improvement of particle resuspension.The main works and conclusions are listed as follows:1.From the perspective of aeroacoustics,the mechanism of flow induced oscillation in rectangular cavity was analyzed,and the influence of the thickness of laminar boundary layer on the particles adhering to the substrate surface was discussed.Taking the particle adhering to the surface in ultrasonic dry cleaning area as research object,the mechanical model and the resuspension model of the particle were established based on JKR model,the principle of moment balance and the combination of the effect of flow field and acoustic field.2.The factors affecting the particle resuspension such as particle radius,mean airflow velocity,ultrasonic frequency,sound pressure level,ay and θ were analyzed by using MATLAB software.The results indicated that the moment of acoustic radiation force is much smaller than the moment of drag force and lift force so that the effect on particle resuspension can be ignored.The ratio of the resuspension moment to the fall moment Mr/Mf increases with the increases of either particle radius or mean airflow velocity.The smaller the particle size is,the less likely it is to be resuspension.Hence a larger mean airflow velocity is needed to break the static equilibrium of the particle.Aiming at the particle with a radius of 0.1~0.5μm,the mean airflow velocity was given in the critical state when the particle is about to be resuspension.3.Taking the air flow channel with variable cross-section in ultrasonic cleaner as research object,the characteristics of flow field and acoustic field about flow induced cavity oscillation was studied by CFD technology and aeroacoustics theory.The results indicated that the large vortex is formed in the cavity of the air flow channel,and the flow direction in the cavity is approximately parallel to a diagonal surface of the cavity.The flow velocity increases when the air passes from the leading edge to the trailing edge of the cavity.The velocity of outlet center tends to be stable after transient oscillation.The arrangement of the cavity in the air flow channel increases the velocity of the outlet center.The periodic flow-induced oscillation in the cavity been demonstrated to exist,and the oscillation is mainly based on the first and second order modes.The oscillation frequency is 1.01 kHz and 12.83 kHz respectively and the acoustic energy in the cavity is mainly concentrated in the first order mode.When the frequency is about 25.3kHz,the peak value of sound pressure level reaches 95 dB approximately.The main source region is the intersection area between the channel center and the leading edge of the cavity,and the main ultrasonic sound region is closer to the intersection area between the channel center and the middle edge of the cavity.The main direction of acoustic radiation is towards the bottom right.The main cause of the mechanism which the sound generated by flow-induced oscillation is that the vortex generates in the intersection area between the channel center and the leading edge of the cavity with a certain frequency.Acoustic wave generates when the vortex develops downstream and finally collides with the back wall of the cavity.When acoustic waves propagate back to the leading edge of the cavity,a new shedding vortex is generated in the shear layer.4.The factors affecting the velocity of channel outlet and acoustic characteristics such as the velocity of channel inlet,the ratio of length to depth of cavity,the group count of cavities and cavity shapes were analyzed.The results indicated that the higher inlet velocity is beneficial to the increase of outlet velocity.The velocity growth rate is relatively low when the ratio of length to depth of cavity is larger or smaller,and only when the choice of the ratio of length to depth of cavity is appropriate,the outlet velocity increases significantly.The outlet velocity increases effectively by adding the group count of cavities.Trapezoidal and angular cavities have no obvious effect on the growth of outlet velocity,and the outlet velocity of arc cavity is the highest.With the increase of the inlet velocity,the oscillation frequency and the sound pressure level increases.The ratio of length to depth of cavity has a great influence on the characteristics of flow induced oscillation and the appropriate choice of the ratio of length to depth of cavity will make the oscillation easier to happen.With the increase of the group count of cavities,the sound pressure level increases obviously and the oscillation frequency increases.The peak value of angular cavity is not obvious,and the trapezoidal cavity has only one obvious energy peak which the energy is not high.Among the four cavity shapes,the sound pressure level of arc cavity is highest,which the peak value can reach nearly 130 dB.Moreover,in the ultrasonic frequency range,the peak sound pressure level of the arc cavity is more than 100 dB on both fifth and sixth modal.It can be seen that flow induced cavity oscillation is most obvious in arc cavity.