Session: 7.4.2 - Fluid-Solid Flows II

Paper Number: 158554

158554 - Morphology and Impact Forces of a Droplet Impacting on a Droplet-Carrying Solid Surface 

Abstract: 

The phenomenon of liquid droplets colliding with solid surfaces are widely found in nature and in industrial applications. During the collision process, the droplet deforms and spreads out on the solid surface, resulting in impact forces or erosion on the surfaces. Many studies have been conducted on single droplet collisions with dry surfaces.The process of single droplet collision is found to be mainly affected by the impact velocity, droplet diameter, droplet density, viscosity and surface tension. However, more droplet impact phenomena occur with not dry surfaces. In contrast, research on droplet collisions with droplet-carrying surfaces is relatively scarce.

In this study, we experimentally investigated the phenomenon of a droplet colliding with a droplet-carrying solid surface. The impact force on the solid surface was measured with a high-precision piezoelectric sensor and the morphological changes during droplet collisions were captured with a high-speed camera. First, a deposited stationary droplet was placed on an aluminium plate. Then, a falling droplet was generated above the plate. The falling droplet underwent a free fall and collided with the deposited droplet. The collision was observed to generate an merged large droplet, and the merged droplet then deform and spread out on the solid surface.  

According to the morphological results, it was found that the deformation process of the droplets was significantly affected by the droplet Re number, which was based on the droplet diameter and collision speed. If the Re number was large, the droplet spreaded fast, and an annular jet might generate between the falling droplet and the deposited droplet. If the Re number was small, the annular jet did not appear. In addition, the spreading velocity of the merged droplet was low at the beginning of the collision, and then increased. This is an obvious difference between the collision of a single droplet with dry surface and with a droplet carrying surface. The impact force finally decreased to 0 as we expected.

According to the measurements of the impact forces, at a high Re number, the impact force increases linearly with time at the beginning of the collision, which corresponds to the time when the droplet spreading rate is low. When the spreading speed of the droplet increases, the rise of the impact force becomes steep. We suspected that the delay of the rapid rise in impact force is related to the process of pressure energy transfer when a droplet collides with the droplet-carrying surface. It is found that the peak impact force of a droplet colliding with the droplet-carrying surface is lower than that of a droplet colliding with the dry surface. However, the mass ratio of deposited droplets to falling droplets (varying from 1 to 2) does not significantly affect the peak and duration of the impact force.

Presenting Author: Jingyin Li Xi'an Jiaotong University

Presenting Author Biography: