Study on the deformation and departure of a bubble attached to a wall in DC/AC electric fields

Abstract

In order to investigate the effects of electric fields on the behavior of a bubble attached to a wall, basic experiments on the deformation and departure of a bubble are carried out under d.c./a.c. applied voltages. In the present study, three types of electrodes are used, to examine the bubble behavior by the nonuniformity of the electric field. For a d.c. electric field, as the applied voltage increases the bubble attached to a wall is more extended in the direction parallel to the imposed electric field, thus the aspect ratio and the contact angle also increase. The bubble departure volume in a nonuniform electric field decreases continuously, while that in a uniform electric field is nearly constant. The present results by the d.c. electric field show that the bubble behavior is significantly affected by the degree of the inhomogeneity of the electrode configuration. For an a.c. electric field, as a preliminary analysis, a general theory on an equivalent dynamic system is extended to derive the bubble oscillation frequency. The analysis predicts that the bubble departure occurs near a resonant frequency. It is observed that the departure process of a bubble in the a.c. electric field is associated with the bubble oscillation which is composed of three different regions. Near the critical voltage, the bubble departure volume drops suddenly. It is also found that the reduction of the bubble departure volume by the a.c. electric field is more effective than in the d.c. electric field case. (C) 1997 Elsevier Science Ltd.