The study of parameter diagram for stable drop-on-demand droplet formation

This study investigates the impact of liquid physical parameters and inlet pressure-driven waveforms on droplet velocities and ligament lengths in drop-on-demand droplet formation. The study employs an incompressible two-phase flow model and the volume of fluid (VOF) method to track the liquid-gas interface. Numerical results reveal that increases in ink density and viscosity are associated with decreased droplet velocity and ligament length. Contrastingly, higher driving pressure amplitudes or periods result in increased droplet velocity. Interestingly, changes in the ink's surface tension coefficient initially raise and then diminish droplet velocity. This notable observation is explained by the conservation of energy during droplet formation. Additionally, a new dimensionless parameter (A(j)), representing the ratio between the pressure gradient and the unsteady inertial force, is introduced to consider the effect of inlet driving-pressure waveform. By integrating the Ohnesorge number (Oh), which combines liquid viscosity and surface tension effects, a phase diagram with coordinates (Oh similar to A(j)) is developed. This diagram identifies five distinct droplet formation modes in the extrusion process based on simulations. The new phase diagram (Oh similar to A(j)) is anticipated to provide significant value for the advancement of drop-on-demand droplet generation technology.