Experimental investigation of the sedimentation behavior of metal droplets in liquid–liquid systems

The accurate sedimentation of metal droplets is of great importance in metal droplet-based three-dimensional printing. Detailed investigations of the process of metal droplet collision in a liquid–liquid system are still lacking, relative to studies on the atmospheric environment. In this study, the dynamics of the sedimentation behavior of metal droplets in a liquid–liquid system are experimentally investigated using a high-speed imaging system. The experimental results showed that with an increased impact velocity, metal droplets successively appear after the collision as coalescence, coalescence accompanied by rebound, and rebound. There is a critical impact velocity between the rebound and coalescence, which is related to the surface tension and droplet size of the metal droplets. Analysis of the mechanism of coalescence showed that mechanical oscillations occur during coalescence, which leads to a variation in the inherent surface tension. The greater the impact velocity, the greater the variation. In addition, a semi-empirical prediction formula for the Weber number and maximum spreading factor in the coalescence of metal droplets is developed. This work provides an improved theoretical understanding and superior practical printing efficiency and quality.