Experimental And Numerical Study Of The Collision Characteristics Between Single Droplet And Spherical Particle

The collision process between droplet and solid spherical particles exists widely in daily life,agricultural production and industry fields,which includs spray drying,fluid catalytic cracking,the interaction between the syrup sprayed by the coating device and drug particles.A detailed study of the dynamic behavior of the collision between droplet and particles has played a crucial role in the study of some natural phenomena and the development of industrial and agricultural technology.Under the experimental conditions,the dynamic process of a single droplet impacting a static spherical particle was recorded by a high-speed camera.The results show that when the size ratio of droplet to particles and impact velocity keep constant,the maximum spread radius coefficient(D^*_max)decreases and the minimum liquid film center height coefficient(H^*_min)increases with the increase of wetting angle.When the wetting angle increases to 138°,the droplet rebounds completely.When the wetting angle and the size ratio of droplet to particles keep constant,the maximum spread radius coefficient(D^*_max)increases and the minimum liquid membrane center height coefficient(H^*_min)decreases with the increase of impact velocity.When the velocity increases to 0.68 m·s^-1,the droplet begins to coat the particle.When the impact velocity and wetting angle keep constant,the larger the size ratio of droplet to particles is,the easier it is for droplet to coat the particles.In this paper,the CLSVOF method was used to simulate the behavior of the droplet colliding with moving spherical particles.The effects of impact velocity,the size ratio of droplet to particles and wetting angle on the collision results were analyzed.The effects of We,surface tension coefficient and viscosity coefficient on the dynamic characteristics of the collision between droplet and superhydrophobic spherical surfaces were also analyzed.In addition,the mechanism of the collision process was studied by velocity field and pressure nephogram.Under the simulation parameters,the results are achieved as follows.When the wetting angle is 140°and the size ratio of droplet to particles is 0.6 with the relative velocity is 0.4 m·s^-1,the droplet rebound completely.When the velocity increases to 1.4 m·s^-1,the droplet break up.When the size ratio of droplet to particles is larger than 1,if the particle surface is a wettable surface,the probability of the droplet coating particles is higher.When the value of We is less than 40,the droplet will bounce off the particle surface as a whole.When the value of We is between 40 and60,the droplet will break up.Part of the droplet will form satellite droplet and fly away from the particle surface,but the others will still contact with the particle surface.When the value of We is larger than 60,the fragmentation degree of droplet increases and the number of satellite droplet increases significantly.The larger the surface tension coefficient is,the faster the droplet rebounds on the particle surface,and the maximum spreading radius coefficient decreases with the increase of the surface tension coefficient.The smaller the viscosity coefficient is,the faster the droplet spreads on the particle surface,and the maximum spreading radius coefficient increases with the decrease of the viscosity coefficient.In the process of the recoil of the droplet colliding with the superhydrophobic spherical particles,the pressure difference inside the droplet,the velocity direction inside the droplet and the moving direction of the air flow around the droplet become the driving force for the droplet to rebound from the sphere.The confusion and uneven size of the velocity direction will make the surface tension of the droplet unstable and cause the droplet fracture.