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

Abstract

The impact of foggy weather on the national economy has become more and more serious with the development of society. Exploring cost-effective artificial fog elimination technology has become a practical need. Acoustic coalescence of droplets is a new atmospheric interference technology, which has the advantages of no chemical pollution, easy operation, and so on. Existing field experiments have successfully observed artificial rainfall or defogging promoted by sound waves. However, there is still a lack of systematic experiments to study the influence of different parameters (frequency, sound power, lasting time of sound waves and initial mass concentration, etc) on the collision-coalescence of droplets under sound waves. In this paper, a series of experimental studies have been carried out in a cloud chamber with 1.7 × 0.52 × 0.52 m. The results show that frequency is an important factor affecting the acoustic coalescence of droplets, and there is an optimal frequency of 300 Hz corresponding to droplets with mode diameters of 2.88 μm in our experiment. Increasing the sound power and lasting time can effectively promote the collision of droplets to form larger droplets. Interestingly, the acoustic coalescence effect of droplets does not increase significantly at the optimal frequency of 300 Hz when the sound power exceeds 75 W and the lasting time exceeds 20 s in our device, which is attributed to the breaking of the larger droplets. The initial mass concentration of the droplet is positively correlated with the droplet growth ratio. In this paper, the frequency of 300 Hz, the sound power of 75 W and the lasting time of 20 s are more reasonable to achieve a cost-effective goal.