Investigation of Droplet-Ejection Characteristics for a Piezoelectric Inkjet Printhead

Numerical simulations are performed to explore the droplet-ejection process for a piezoelectric inkjet printhead. In the analysis, the theoretical model takes account of a set of three-dimensional, time-dependent conservation equations of mass and momentum, with the incorporation of the continuous surface force model for treating the interfacial surface tension effect. The resultant governing equations are solved using an iterative semi-implicit method for pressure-linked equations consistent algorithm for resolving flow properties. The volume-of-fluid method along with the piecewise linear-interface construction technique is implemented to characterize the behaviour of liquid surface movement. With a typical piezodiaphragm printhead as an illustration case, the time evolution of the gas-liquid interface is calculated for an entire ejection cycle of 164 μs. The predicted droplet shapes throughout the ejection process are compared with microphotographed images for the verification of the present theoretical formulation. The flow and transport phenomena in the stages of the ink ejection and the droplet formation are further examined in detail. In response to design needs, the study is extended to determine the variations of ejection characteristics at different settings of nozzle exit diameter, ejection time interval, surface tension, and viscosity of fluid.