Drops ejection from a capillary nozzle by Drop-On-Demand technology
Abstract
Drop-on-Demand (DOD) technology enables to control the ejection of drops, from a vertically capillary nozzle, by piezoelectric stimulation. DOD applies in microfluidics, from the ink-jet printers to Bio-MEMS. This study emphasizes on the numerical simulation of the drop evolution during its formation and ejection by DOD technology. The highly distorted interface evolution represents an axisymmetric transient free-boundary problem, which is modelled here through a Boundary Element Method. An irrotational flow model can reproduce most observed experimental data on drop size, velocity, frequency, and conditions for non-satellite formation. Viscous effects are included to some extent, as it is allowed for potential flows of fluids with constant viscosity, the normal viscous stress at the interface being expressed in terms of the velocity potential. The time progression is made with a 4th order Runge-Kutta explicit numerical scheme. The time step is varied upon a stability criterion. The interface evolution is determined through a Lagrangian description of a variable number of nodes, unevenly redistributed on the boundary at each time step. The numerical code accuracy is evaluated through the global mechanical energy balance, expressed only in surface integrals terms. Our computed results fit well the available DOD data for ejected drops with volume of picolitres order.
Origin : Files produced by the author(s)
Loading...