Effects of capillary spacing on EHD spraying from an array of cone jets

Electrohydrodynamic (EHD) sprays are fundamentally characterized by low liquid flows that are atomized into relatively small, monodisperse droplets. Since previous studies have shown that droplet size increases with increasing flow rate, the current work employs an array of capillaries intending to increase fluid throughput without increasing the size of the droplets produced. To do this, an array of four-capillary nozzles is examined by measuring the required potential needed for stable EHD spraying in the cone-jet mode as a function of capillary separation. In addition, a simple electrostatic model is used to support the experimental results, and to predict the behavior of a larger, 5 x 5 square array. Results show that the potential required for cone-jet spraying in a two-dimensional array of capillaries generally increases as the capillary spacing decreases (due to electrical shielding), but at very close spacing the potential can decrease if the neighboring capillaries are dry. This result suggests that EHD arrays can benefit from fine wire electrodes interspersed among the capillaries. (C) 2002 Elsevier Science Ltd. All rights reserved.