Modeling and characterization of metal droplets generation by using a pneumatic drop-on-demand generator

A 2D axisymmetric model has been proposed to study the mechanism of the droplet generation by using a pneumatic drop-on-demand (DOD) generator. A proprietary pneumatic DOD generator was also applied to conduct droplet generation experiments. The validity of the proposed model was verified through the simulation results of droplet pattern, breakup length distance and droplet diameter, which were in good agreement with the experimental ones. Theoretical studies were conducted to characterize the metal droplet generation using pneumatic DOD technique. Theoretical analyses show that metal droplets break away from jets in front of the sphere ends due to the increase of the capillary disturbance at a very small Ohnesorge number (Oh < 0.01). This capillary disturbance is caused by the action of surface tension. Shapes of droplets do not significantly change because of the relatively low pressure inside droplets. The droplet diameter decreases when the nozzle diameter decreases to 100 μm, while the ratio of droplet diameter to nozzle diameter increases rapidly. An external disturbance with high frequency should be introduced to accelerate the metal jet breakup for further decreasing the droplet size. This work offers a useful guide for choosing appropriate parameters to generate metal droplets using pneumatic DOD technique.