Electrostatic charging and deflection of nonconventional droplet streams formed from capillary stream breakup

Abstract

Droplet streams generated from capillary stream breakup and forced with amplitude-modulated ͑a-m͒ disturbances will undergo a systematic interdroplet merging process due to their relative velocities that result from the am disturbance. This paper concerns the electrostatic charging of droplets generated with am disturbances, and seeks an understanding between the competitive effects of the electrostatic repulsive force and the momentum associated with relative velocities that are due to the am disturbance. To this end, experimental results and numerical simulations that are in excellent agreement and predict the configuration of the charged droplet stream are presented. In this work, droplets are generated with the aforementioned technique and are electrostatically charged. It has been found that for droplets generated with a disturbance with a high degree of modulation, m, the momentum of the droplets dominates over the electrostatic force causing the droplet merging process to be similar to the uncharged case as attested by both experimental results and numerical simulations. Here, m is the ratio of modulation to original carrier amplitudes. For droplets with lower values of m, the electrostatic forces dominate and it is found that the relative positions of the droplets will oscillate along the direction of their flight path with maximum excursions not exceeding one wavelength of the carrier disturbance ͑i.e., the separation of the unmerged droplets͒.

Periodic emission of droplets from an oscillating electrified meniscus of a low-viscosity, highly conductive liquid

“…The same requirements apply in drug discovery experiments for medical applications [9,10], without forgetting the direct delivery through lung deposition via monodisperse aerosols of droplets with diameters between 3 and 5 μm. Other applications include optics [18,19], where the microdrops are used as lenses themselves, manufacturing of complex composite solids, such as directional asymmetric metal-ceramic matrices [20,21], direct soldering [22][23][24][25], thin-film coatings, and many more.…”

Droplet charging regimes for ultrasonic atomization of a liquid electrolyte in an external electric field

“…One such technique exploits the piezoelectrically induced instabilities of a pressure-driven jet, resulting in Rayleigh breakup. 7,8,19,22,23,31,32 Methods of incorporating pulsedelectric-field-induced instabilities for jet breakup have also been introduced. 31 The latter family of techniques, irrespective of the application, incorporates a charging electrode in the region of capillary jet breakup to induce preferential charge transport into the forming droplet.…”

“…31 The latter family of techniques, irrespective of the application, incorporates a charging electrode in the region of capillary jet breakup to induce preferential charge transport into the forming droplet. In the cases of ink jet printing 7,8,13,31 and drop-on-demand manufacturing, 22,23 the flight path of these charged droplets is appropriately controlled as they traverse through an in-flight electric field to achieve a desired deposition ͑printing͒ pattern. In a similar manner, Grimm and Beauchamp 19 charged droplets emitted from a vibrating orifice aerosol generator, followed by an induced droplet fission as the droplets fly through an elevated electric field region for mass spectrometry applications.…”

“…Another common technique, electrohydrodynamic atomization and tip streaming, relies on the application of a high electric field for fluid dispersion. [10][11][12][13][14] Still, there is a wide range of techniques for production of discretely charged droplets for applications including mass spectrometry, [15][16][17][18][19][20][21] drop-on-demand manufacturing of multilayer parts and circuits, 22,23 spray coatings, 24,25 biosensing and other lab-on-a-chip applications, [26][27][28][29] and wet scrubber systems for pollution control, 30 among others. The focus of this work is on mechanically driven atomization, which is coupled to an external electric field for droplet charging.…”

“…Drop-ondemand manufacturing applications utilize charged droplets in a similar manner to ink jet printing. 22,23 In high-resolution printing and/or manufacturing, the droplet charging and electric fields must be accurately controlled to achieve a desired printing quality. For example, Orme et al 22 demonstrated the use of a pulsed charging signal for generating precisely charged droplets of a eutectic solder.…”