Pulsating emission of droplets from an electrified meniscus

Abstract

A numerical description is given for the pulsating emission of droplets from an electrified meniscus of an inviscid liquid of infinite electrical conductivity which is injected at a constant flow rate into a region of uniform, continuous or time periodic, electric field. Under a continuous field, the meniscus attains a periodic regime in which bursts of tiny droplets are emitted from its tip. At low electric fields this regime consists of sequences of emission bursts interspersed with sequences of meniscus oscillations without droplet emission, while at higher fields the bursts occur periodically. These results are in qualitative agreement with experimental results in the literature. Under a time periodic electric field with square waveform, the electric stress that acts on the surface of the liquid while the field is on may generate a tip that emits tiny droplets or may accelerate part of the meniscus and lead to a second emission mode in which a few large droplets are emitted after the electric field is turned off. Conditions under which each emission mode or a combination of the two are realized are discussed for low frequency oscillatory fields. A simplified model is proposed for high electric field frequencies, of the order of the capillary frequency of the meniscus. This model allows computing the average emission rate as a function of the amplitude, duration and bias of the electric field square wave, and shows that droplet emission fails to follow the applied field above a certain frequency.

Periodic emission of droplets from an oscillating electrified meniscus of a low-viscosity, highly conductive liquid

“…Kim et al [34], Kang et al [35], and Lee et al [36] achieved improved control of the size and emission frequency of the droplets by using pulsed electric fields and partially classified the new dripping modes that appear in these conditions. Higuera et al [37] numerically analyzed the pulsating emission from a meniscus of an inviscid liquid of infinite electrical conductivity in a simplified configuration, qualitatively reproducing experimental results for constant and pulsed voltages. Further steps toward the practical implementation of these techniques for high-speed and drop-on-demand EHD printing have been taken by Mishra et al [38] and Sutanto et al [39].…”

“…[37] for an inviscid liquid of infinite electrical conductivity that is injected at a constant flow rate through an orifice in a metallic plate into a region of uniform electric field. The numerical results reproduce the main features of the periodic dynamics, including the stretching of the meniscus, the formation of a ligament whose tip emits a spray of tiny droplets and eventually detaches, and the subsequent recoil of the meniscus.…”

Mechanisms, Capabilities, and Applications of High‐Resolution Electrohydrodynamic Jet Printing

“…An important aspect of such modeling studies is their ability to reveal details that are difficult or impossible to measure using experimental approaches. Higuera et al used numerical calculations to reveal the distribution of the electrical stress on the meniscus that forms at the tip of the nozzle and different modes of pulsation as a function of time. A numerical study performed by Kim et al explored the impact of wetting behavior of the nozzle.…”

Controlled cavity collapse: scaling laws of drop formation

“…In fact, in other phenomena, this energy surplus may come from several sources, e.g. the film's surface energy in bubble bursting, 24 the surface electrical charge in the onset of electrospray, [31][32][33][34][35] or the kinetic energy in drops impacting a liquid pool. 28 In our system, this energy is introduced by the piston.…”