Spark-induced drops and jets

When a high-voltage capacitor is discharged between two electrodes in a conducting liquid, the resulting spark can create a rapidly expanding cavitation bubble that sends out a shock wave. We exploit this phenomenon in fine capillary tubes to create high-speed liquid jets that could be used for intradermal drug delivery. Depending on the voltage discharge, we can observe either a drop or a focused jet with speed in the range O(10¹-10²) m/s. We conducted a systematic study to understand the role of various parameters such as fluid viscosity, capillary geometry, and voltage on the speed and shape of the jet or drop. The transition between the droplet and jet regimes is primarily governed by the location of the spark relative to the open end of the capillary, as well as liquid viscosity, and discharge voltage. In the jet regime, the speed is dictated by the discharge voltage. We propose a robust system to generate drop/jet-on-demand using low voltage discharge techniques. This system is useful in various applications such as inkjet printing, coating techniques, and needle-free jet injections.