Stability and atomization characteristics of electrohydrodynamic jets in the cone-jet and multi-jet modes

The stability and atomization characteristics of electrohydrodynamic (EHD) jets have been investigated experimentally. EHD jets were formed by forcing propylene glycol at a steady flow rate through a charged capillary tube. The capillary tube had an outer diameter of 890 mu m, the electric potential applied to the tube ranged from 0 to 20 kV, the liquid how rate ranged from 100 to 500 mu l min(-1), and the gap between the tube and ground ranged from 2.5 to 5.0 cm. Observations of the fluid discharge from the capillary were made with a CCD system with a microscopic lens attachment and a synchronized strobe lamp. In general, a single jet emanating from a conical meniscus (cone-jet) was observed to be stable at applied voltages on the order of 5-10 kV. The stable configuration at higher applied voltages was a ring of smaller jets emanating from the periphery of the capillary (multi-jet). Some hysteresis was observed in the stability of each configuration. The resulting droplets in the cone-jet configuration tend to be roughly 10 times smaller than the capillary, while the droplets that break off in the multi-jet mode are roughly 30 times smaller than the capillary. The implications of the stable multi-jet mode are that for a given flow rate, smaller droplets can be produced in the multi-jet mode than in the cone-jet mode. (C) 2000 Elsevier Science Ltd. All rights reserved