Pulsating electrohydrodynamic cone-jets: from choked jet to oscillating cone

Pulsating cone-jets occur in a variety of electrostatic spraying and printing systems. This paper reports an experimental study of the pulsation frequency to reconcile two models based on a choked jet and an oscillating cone, respectively. The two regimes are demarcated by the ratio of the supplied flow rate (Q(s)) to the minimum flow rate (Q(m)) required for a steady Taylor cone-jet. When Q(s) less than or similar to Q(m), the electrohydrodynamic flow is choked at the nozzle because the intermittent jet, when on, emits mass at the minimum flow rate; the pulsation frequency in the choked jet regime is proportional to Q(s)/Q(m). When Q(s) greater than or similar to Q(m), the Taylor cone anchored at the nozzle experiences a capillary oscillation analogous to the Rayleigh mode of a free drop; the pulsation frequency in the oscillating cone regime plateaus to the capillary oscillation frequency, which is independent of Q(s)/Q(m).