Development of a high-speed capacitive surface sensor for fluid distribution imaging

Experimental investigation of multiphase flows plays an important role in many research and industrial application areas. We introduce a novel surface sensor based on electrical capacitance (permittivity) measurements to imaging near-wall fluid distributions of multiphase flows. The sensor is formed by 32 x 32 interdigitated sensing structures and can be mounted on the edges of a pipe or vessel and thus has a minimal influence on the flow. An associated electronics measures the capacitance of the fluid overlaying each sensing structure in a multiplexed manner. This way, images of the fluid distribution can be achieved directly without the need for any reconstruction procedure. Images at up to 10,000 frames per second can be obtained. The system was evaluated showing good reproducibility and adequate accuracy. The system is able to well distinguish permittivity differences of up to one, which corresponds, for instance, to a two-phase flow of air and oil (rel. permittivity about 2).