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.

Experimental and theoretical study of a cone-jet for an electrospray microthruster considering the interference effect in an array of nozzles

“…Snarski and Dunn (1991) studied the interaction between two sprays of electrically charged liquid droplets. Almekinders and Jones (1999) reported an injector with 24 electrospray emitters equidistantly arranged for atomizing oil with very low conductivity.…”

Design, Fabrication, and Characterization of Linear Multiplexed Electrospray Atomizers Micro-Machined from Metal and Polymers

“…Equation (3) suggests that the projection of spray on x-z plane resemble an isosceles triangle. The y-expansion is primarily determined by the spray axis bending, caused by the repelling force exerted by other sprays (Snarski and Dunn 1991). By approximating the spray as a lineof-charge (Deng and Gomez 2007), we can treat axis bending of the spray at the edge as the result of E y , which is the radial component of the electric field introduced by all other line-ofcharge:…”

“…The three electrode configuration is crucial to enable operation of high nozzle packing densities in the cone-jet mode, effectively dividing the device into two electric field regions so that space charge can be mitigated to provide equal electric fields at each cone-jet site . To date, at least four various fabrication routes to MES have been attempted: (1) "brute force," where multiple individual stainless steel (Snarski and Dunn 1991;Rulison and Flagan 1993;Regele et al 2002;Hubacz and Marijnissen 2003;Jaworek et al 2006;Si et al 2007) or fused silica (Kelly et al 2008) capillaries are integrated together into a single device; (2) silicon microfabrication (Xue et al 1997;Tai et al 2002;Xiong et al 2002;Velazquez-Garcia et al 2006;Kim et al 2007;Mao et al 2011); (3) soft lithography Wang et al 2004;Choi et al 2011); and (4) conventional machining (Almekinders and Jones 1999;Tang et al 2001;Bocanegra et al 2006;Duby et al 2006;Si et al 2010;Arnanthigo et al 2011;Lhernould and Lambert 2011).…”

Producing Pharmaceutical Particles via Electrospraying with an Emphasis on Nano and Nano Structured Particles - A Review

“…Studies of Snarski andDunn 1991, andRulison andFlagan 1994 show that the voltage required for the steady cone-jet mode increases with a decrease in distance between the capillary nozzles. As the distance decreases in order to increase the nozzle packing density further issues will arise.…”