Investigation on collision-coalescence of droplets under the synergistic effect of charge and sound waves: orthogonal design optimization

Abstract

As an efficient approach to improve visibility, defogging technology is essential for the operation of ports and airports. This paper proposes a new and hybrid defogging technology, i.e. an electric–acoustic defogging method. Specifically, the droplets are charged by corona discharge, which is beneficial to overcome the hydrodynamic interaction force to improve the droplet collision efficiency. Meanwhile, sound waves (especially acoustic turbulence) promote the relative movement of droplets to increase the collision probability. In this study, the effects of acoustic frequency (f), sound pressure level (SPL), and voltage (V) on the droplet growth ratio were studied by orthogonal design analysis. The results of difference analysis and multi-factor variance analysis show that frequency and SPL are the dominant factors that affect the collision of droplets, and the effect of voltage is relatively weak. And f= 400 Hz, SPL = 132 dB, and V = −7.2 kV are the optimal parameters in our experiment. In addition, we further studied the impact of single factor on droplet growth ratio. The results show that there exists an experimental optimal frequency of 400 Hz. The droplet growth ratio increases with SPL and voltage level. The new technology proposed in this paper can provide a new approach for defogging in open space.

Numerical simulation of the enhancing effect of micro–nano protrusions on electrostatic fog harvesting

“…To further enhance the discharge current by increasing the number of micro-nano protrusions is a spontaneous idea. However, the results in table 3 show that the discharge current under the barbed wire with two protrusions is only slightly higher (less than 9%) than that with only one protrusion (type [5][6][7][8][9][10][11]. To further study the underlying mechanism, the electric field intensity and local charge density at 2.5 mm above the ground electrode are extracted and plotted in figures 8(b) and (c), respectively.…”

“…Several field trials carried out in Oman [2], the Philippines [3], California [4] and others have confirmed the feasibility of fog harvesting. To enhance fog collection, researchers have proposed a variety of multi-functional methods, such as biomimetic surfaces from plants and animals [5,6], multi-layer harvesters [7,8], acoustic-induced droplet collision-coalescence [9,10], surface chemistry wettability [11][12][13] and electrostatic fog harvesting [14,15].…”

Investigation of critical response characteristics of micro-droplets under the action of low-frequency acoustic waves

“…For 40-100 Hz acoustic intervention on microdroplets, Bai et al (2020); Bai et al (2021a); Bai et al (2021b) found that the particle size increment was significantly affected by the sound frequency, and the droplets isotope values increased after interference of acoustics. He et al (2021) conducted experiments on droplets by combined sound waves of 200-600 Hz and electric field. The effects of sound wave and electricity on droplet agglomeration have been proved, and the optimal sound frequency was 400 Hz.…”