Quantitative Prediction of a Moving Axisymmetric Void Using Parallel Wire-Type Capacitive Sensor

A unique measurement scheme for determining the shape of an axisymmetric bubble propagating through a nonconductive liquid is proposed. The method uses a set of parallel wire capacitive probes capable of measuring the thickness of the dielectric layers between the electrodes. First, the probe capacitance has been determined in terms of void fraction and electrode geometry through a theoretical calculation. A 3-D numerical simulation has also been performed to estimate the probe capacitance with varying liquid film thickness. The time-varying probe response and the propagation velocity of the void are obtained experimentally. Then the developed electrodynamic models, with the help of the above two information, estimate the film thickness profile and reconstruct the void geometry. A comparison with the photographic image of the bubble reveals that the numerical method yields a better match than the theoretical model.