A field-focusing imaging sensor for fast visualization of multiphase flows

A novel imaging sensor based on multichannel capacitance measurement is introduced in this paper. The field-focusing sensor uses a multitude of strip electrodes located at two opposing and parallel walls of a vessel, whereby the opposing electrodes run perpendicular to each other. By the use of a special multiplexed excitation-sensing scheme a focusing of the electrical field to well-defined regions within the sensor is achieved which allows the sensor to individually interrogate each one of those regions and thus to two dimensionally map the flow constituents contained by the sensor. Associated electronics can generate up to 625 frames per second. The sensor can be considered as a high-speed capacitance 'camera' for a channel flow. Electrical field simulations with finite element method confirm the focusing effect explored by the sensor. The imaging capability is shown by the visualization of a stratified air–water mixture. Furthermore, the sensor was used to monitor the transient behaviour of the mixing of two substances with different densities.