Measurement of reference velocity vector for four-sensor conductance probes using orthogonal, high speed cameras

This paper describes a new miniaturised 4-sensor probe which minimises the bubble probe interaction. It goes on to introduce a camera based reference measurement system
which will be used to quantify the accuracy with which a 4-sensor probe can measure the velocity vector of air bubbles in water. Results are presented for a series of experiments in which measurements from a 4-sensor conductance probe of the polar angle, the
azimuthal angle and the magnitude of the bubble velocity vector are compared with reference values of these quantities. The mean error in the polar angle measured by the probe was 1.32º, the mean error in the azimuthal angle measured by the probe was -0.1º and the mean percentage error in the measured velocity magnitude measured by the probe was 0.8%. These are believed to be best results yet obtained when using a 4-sensor probe to measure the velocity vectors of relatively small bubbles (with a major axis of less than 10mm and a minor axis of about 5mm).