Mechanism of Cloud Droplet Motion under Sound Wave Actions

Abstract

Sound waves have proven to be effective in promoting the interaction and aggregation of droplets. It is necessary to theoretically study the motion of particles in sound field to develop new acoustic technology for precipitation enhancement. In this paper, the motion of cloud droplets due to a traveling sound wave field emitted from the ground to the air is simulated using the motion equation of point particles. The force condition of the particles in the oscillating flow field is analysed. Meanwhile, the effects of droplet size, sound frequency, and Sound Pressure Level (SPL) on the velocity and displacement of the droplets are also investigated. The results show that Stokes force and gravity play a dominant role in the falling process of cloud droplets, and the effect of sound wave is mainly reflected in the fluctuation of velocity and displacement, which also promotes the displacement of cloud droplets to a certain extent. The maximum displacement increments of cloud droplets of 10 µm can reach 9,200 µm due to the action of sound waves of 50 Hz and 143.4 dB. The SPL required for a noticeable velocity fluctuation for droplets of 10 µm with frequency of 50 Hz is 88.2 dB. When SPL < 100 dB and frequency > 500 Hz, the effect is negligible. The cloud droplet size plays a significant role in the motion, and the sound action is weaker for larger particles. For a smaller sound frequency and higher SPL, the effect of the sound wave is more prominent.

Tuning Electrospray Ionization with Low-Frequency Sound

“…It was previously reported thatin the presence of a strong sound fieldmicroparticles undergo so-called acoustic agglomeration; i.e., their movements are affected in such a way that the microparticles approach one another. − In fact, acoustic agglomeration is an effective way to remove dust, particles, and droplets by using generated sound waves. − Both theoretical and experimental studies indicate that the sound waves with high sound pressure level (∼100 dB) and low frequency (<500 Hz) have a carrying effect on microparticles. ,,, In the present study involving ESI microdroplets, the effect was noticeable when the sound pressure level was above 100 dB and the frequency was below 400 Hz (cf. Figure S18).…”

“…38−41 Both theoretical and experimental studies indicate that the sound waves with high sound pressure level (∼100 dB) and low frequency (<500 Hz) have a carrying effect on microparticles. 35,37,38,42 In the present study involving ESI microdroplets, the effect was noticeable when the sound pressure level was above 100 dB and the frequency was below 400 Hz (cf. Figure S18).…”

Experimental study on coalescence of fog droplets in cloud chamber under low-frequency sound waves

“…However, the droplet growth ratio is 3.60 at a frequency of 400 Hz, and the droplet growth ratio is only 1.49 at a frequency of 200 Hz. Moreover, the experimental results also show that the effect of the sound waves on the droplet growth ratio gradually decreases for higher frequencies than 500 Hz [25]. That is, high-frequency sound waves are not conducive to the applications of fog elimination or rainfall.…”

Review of Acoustic Agglomeration Technology Research

“…Tulaikova T V et al 71 further explored the theoretical underpinnings and practicability of acoustic methods in enhancing rainfall. Li 72 et al utilized the point particle motion equation to simulate cloud droplets' movement induced by ground-emitted traveling acoustic waves, examining the influence of droplet size, acoustic frequency, and sound pressure level on droplet velocity and displacement. For droplets measuring 50 μm, the conditions for significant displacement fluctuations were identified as 10 Hz and 88.2 dB.…”