Similarities and differences in electrocoalescence processes of conducting uncharged droplets at the DC and pulsed voltage

This article investigates the electrical coalescence processes under pulsed DC voltage. The study aims to provide a physical explanation for the effect of voltage frequency on electrocoalescence and to compare it with constant DC voltage to identify differences and assess the potential advantages of pulsed DC voltage in electrostatic dehydration. A numerical model based on the arbitrary Lagrangian–Eulerian method is employed to simulate the electrocoalescence process. The model accounts for the behavior of a two-phase system consisting of a dielectric dispersion medium (oil) and a conductive dispersed phase (water). The results indicate that, in both the high-frequency range above the characteristic frequency of droplet oscillations and the extremely low-frequency range, the electrocoalescence process behaves similarly to the case with constant DC voltage. However, in the frequency range near the characteristic frequency, a slight increase in the threshold for the transition from coalescence to non-coalescence is observed, due to the temporary absence of voltage following the formation of a bridge between droplets. Nevertheless, this threshold increase is limited to approximately 5 % and remains probabilistic, as it depends on the phase of the voltage signal at the moment of contact. Additionally, at the characteristic frequency, coalescence results in the formation of smaller droplets rather than larger ones, negatively impacting the overall efficiency of the cleaning process.