Linear dynamics modelling of droplet deformation in a pulsatile electric field

Abstract

Resonance is possible only when the droplets are sufficiently large (i.e. for Ohnesorge number less than 1). The oscillation amplitude decreases rapidly with the electric field frequency. A qualitative comparison with some experiments of droplet-interface coalescence available in the literature has also been addressed, suggesting a correlation between the formation of secondary droplets and the amplitude of oscillation of the mother droplet. The outcomes of this analysis can be useful for the selection of the best operating conditions to improve the electrocoalescence process efficiency, as they can provide guidelines to the choice of the most suitable electric field parameters.

Droplet deformation under pulsatile electric fields

“…7 also shows that the oscillation amplitudes are negligible at high frequencies (f >500 Hz). Low oscillation amplitudes are likely to suppress the occurrence of secondary droplets [18]. In addition, it is seen in Fig.…”

“…In Fig. 7, the linear model predictions of Vivacqua et al [18] are compared with the simulation results for identical conditions in terms of amplitude of the oscillatory response. The results of simulation and linear model have similar trends, especially at high frequencies (f 100Hz).…”

“…Droplet deformation in the presence of an externally applied electric field is very common in many industries, including electrospining [15], electrospraying [16] and electrowetting [17], etc. A good number of experimental and numerical works have been conducted on droplet deformation under an electric field [18][19][20][21][22][23][24]. Taylor [25] proposed an electrohydrodynamic model, generally referred as the "leaky dielectric model", for droplet deformation, with the assumptions of neutral droplets, quasi-static electric field, small deformation, and free convection charge.…”

“…Moreover, a number of new models have been proposed over the past decades [26,28,29]. Most recently, Vivacqua et al [18] proposed a linear dynamics model under pulsatile fields with various waveforms as forcing terms, namely half-sinusoidal, square and sawtooth waves. They reported that the droplet deformation was affected by the electric field type stimulus.…”

Non‐coalescence behavior of neutral droplets suspended in oil under a direct current electric field

“…Basically, the oil–water separation efficiency at the macro level depends on dynamic behaviors of droplets in the emulsion under the action of electric field. To understanding droplet motion, deformation, breakup, coalescence, and their dynamics in the electric field, a large number of theoretical, experimental, and numerical studies have been carried out . The coalescence of two droplets caused by electric field usually involves three major stages: (1) the mutual attraction and approach of two droplets; (2) the drainage of liquid film; (3) the merging of two droplets.…”