Polarization motion of bubbles in a non-uniform electric field

Abstract

In this study, the polarization motion of bubbles in a determined dielectric liquid medium (n-heptane) under a direct current (DC) non-uniform electric field were experimentally studied, using high-speed photography and with a focus on the effect of applied voltage and gas flow rate on bubble dispersion characteristics. The results show that increasing the electric field strength leads to a shortening of the bubble growth period, a significant reduction in bubble size and a rapid generation frequency. At low electric field strength, the bubble motion mainly exhibits hydrodynamic characteristics, and the height of the bubble chain shortens with the increase of BoE as a result of wake effect. In contrast, at high electric field strength, the bubble motion is first governed by polarization force and manifests electrohydrodynamic (EHD) characteristics, and the height of the bubble chain extends upward with increasing electrical Bond number (BoE). Nevertheless, once the bubbles leave the region dominated by the polarization force, their motion again displays hydrodynamic characteristics, and then the bubbles spread out the liquid phase, subject to bubble wakes and bubble-to-bubble interaction behaviors. In addition, two typical regimes of bubble coalescence are divided depending on the coalescence positions, including the coalescence near the tube orifice and the coalescence at the end of the bubble chain. The bubble size distribution at different heights corresponds to the bubble coalescence regimes.