Experimental study on the action of electric field on growing gas bubbles by measuring the variation of their curvature

The study of bubble dynamics is precursory to the understanding of the more complex heat and mass transfer technical issues involving them, like phase separation and boiling. In particular, it is well known that the application of an electric field affects bubble growth and detachment in a fluid and may improve boiling heat transfer performance. An extremely simple experiment was operated to achieve a better comprehension of EHD phenomena on gas bubbles: a single gas bubble was injected into a still dielectric fluid through an orifice in a flat plate; the injection device allowed very slow growth, or even the creation of a fully static bubble. A d.c. electric field could be imposed in the system by means of an electrode laid parallel to the plate. The image of the bubble was acquired and processed via a dedicated software, to obtain its geometrical parameters and the forces acting on it. The overall vertical force balance on the bubble was experimentally verified in the absence of electric field to qualify the method. The resulting electric force in the presence of EF is then determined and compared successfully with a numerical evaluation by COMSOL code. Finally, the local curvature of the bubble profile was obtained from image processing, and its value was compared with the trend predicted by the capillary equation, extended to include EHD phenomena. The last comparison evidenced the need of further clarification of the mechanisms governing electrical interfacial stress