Experiments characterizing the interaction between two sprays of electrically charged liquid droplets

Abstract

Experiments were conducted to characterize the interaction between two sprays of electrically charged ethanol droplets. The micrometer-size droplet sprays were generated electrohydrodynamically by applying a high positive voltage to two adjacent parallel needles that were located above a distant, electrically grounded funnel. The resultant droplet axial and lateral velocity components and diameter were measured as a function of needle spacing and applied voltage using a Phase Doppler Particle Analyzer. Data were acquired at two axial positions below the needles' tips, for two needle spacings, four applied voltages and at a single flow rate.

The results revealed that an increase in applied voltage yielded an increase in the spray charge density. This produced an increase in both the axial and lateral droplet velocity components and a decrease in the droplet Sauter mean diameter and in its variation across the spray. An increase in needle spacing yielded a decrease in the axial velocity component. The lateral velocity component and the Sauter mean diameter, however, were not noticeably affected by this increase. Photographic data established a relationship between the lateral half-width of the spray and axial distance. This was used to identify a nondimensional similarity between the axial mean velocity component and lateral position. The results collectively support that appropriate variations in the applied voltage and needle spacing can yield more spatially uniform mean velocity component and Sauter mean diameter profiles. These variations bring about increased mixing between the two needles' sprays and, thus, an enhanced development of the combined droplet spray.