Numerical study on the effects of non-dimensional parameters on drop-on-demand droplet formation dynamics and printability range in the up-scaled model

The droplet formation dynamics from a drop-on-demand printhead is numerically investigated with regard to the printability range. The numerical simulation is carried out using a volume-of-fluid model, and the qualitative effects of non-dimensional parameters on the droplet formation dynamics are evaluated. To determine the printability range, within which the droplet is ejected in a stable manner without satellite droplets, extensive numerical simulations are carried out by varying the viscosity and surface tension. Generally, the printability range is determined by a Z number, which is the inverse of the Ohnesorge number (Oh). However, it is found that the Z number alone is insufficient for describing the droplet formation dynamics. Other important non-dimensional parameters such as the Reynolds number (Re), Weber number (We), and capillary number (Ca) should also be taken into consideration. For studying the printability, the droplet formation dynamics are divided into five different regimes, and a regime map based on the Z, We, and Ca is proposed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742913]