Session: 10.2.2 - Interfacial Phenomena and Flows II

Paper Number: 158229

158229 - Study of the Droplets Collision Process and the Influence on Velocity and Pressure Fields 

Abstract: 

The phenomena of gas-liquid phase transition, atomization, and gas-liquid separation are ubiquitous both in nature and industry, and their essences are all related to the size of the dispersed liquid droplets. The primary factors affecting the droplet size are the collision process between droplets and the interactions between the gas and liquid phases. The aim of this article is to reveal the intrinsic relevance between the unsteady evolution process of droplets after collision and the velocity and pressure fields inside and around the droplets, and thereby interpreting the mechanism of droplets coalescence and breakup process clearly. In this work, the droplets collision process was studied through numerical simulation methods, and the force applying to the droplets and deformation resulting from the collisions were analyzed. The influences of factors such as droplet size, collision velocity, and eccentricity on the velocity and pressure fields inside and around the droplets were investigated. The results show that the influence of small droplets collision on the surrounding flow field is minor, while the influence of large droplets collision on the flow field is more prominent. In a head-on collision, the velocity field is almost symmetry for the small droplets colliding with a small relative velocity. However, if the collision velocity is higher, vortices are appeared, and the number of the vortices increase with the increase in the collision velocity. Regardless of head-on collision or eccentric collision, the pressure field is almost symmetry in all cases of droplet sizes and collision velocities. However, if the droplets collide at a higher velocity, the contact between droplets may cause a sharp increase in regional pressure due to some gas may failure to be discharged quickly. With regards to the velocity field distribution of eccentric collision, the outcome is complex and unpredictable. Because the vortex intensity produced by the collision is very strong when the eccentricity is small, it is difficult to reach a dynamic stability. With the increase in the eccentricity, the droplets are more likely to rotate, which drives the flow of surrounding gas, and thereby consuming the energy. As a result, the velocity can rapidly reach a dynamic stability state. The research results suggest that the evolution process of droplets after collision is a consequence of the combined effects of the collision force and the change of velocity and pressure fields inside and around the droplets. To study the change in the velocity and pressure fields during the droplet collision process is beneficial to optimize and control industrial processes such as atomization and gas-liquid separation.

Presenting Author: Shuxia Yuan Xi'an Shiyou University

Presenting Author Biography: Dr. Shuxia Yuan, is a professor in the School of Mechanical Engineering at Xi’an Shiyou University, Xi’an, China. She was graduated from Xi’an Jiaotong University, and be awarded a PhD degree in 2012. She was worked as a visit scholar in the University of Tulsa, OK, US, from March 2017 to March 2018. Her current research field include Separation, Fluid Mechanics, Multiphase Flow, and safety of pressure vessel & pipeline.