Dynamics of bubble formation on submerged capillaries in a non-uniform direct current electric field

Abstract

In this paper, the dynamic behaviors of bubbles in ethanol were investigated with a needle-ring electrode rig in the presence of a direct current (DC) electric field. High-speed photography was used to capture the bubble dynamic characteristics under various electric field strengths. The obtained results show that the applied electric field accelerates the bubble formation speed and release frequency, but restricts the bubble release diameter. Meanwhile, high electric field strength causes the bubble shape being squeezed in horizontal direction and stretched in vertical direction, respectively. Quantitatively, the evolutions of the bubble non-dimensional size parameter δ reflect that producing the bubbles whose width are smaller than those of orifice is to judiciously control the electric field strength, which is not closely related to the capillary model. The bubble aspect ratio χ and the non-dimensional contact angle θb/θs depend primarily on electric field strength and show a desirable corresponding relationship with the bubble deformation and the triple-phase contact line, respectively. Furthermore, by combining the bubble evolution with the dimensionless Eötvös number (Eo), Weber number (We) and electrical Bond number (BoE), the main forces work on the bubble and surrounding liquid are evaluated and elaborated.