Optical development and application of a two colour LDA system for the simultaneous measurement of particle size and particle velocity

A non-invasive optical technique has been developed which can simultaneously measure drop size and velocity. The instrument is suitable for application to enclosed two phase flows with limited optical access. The dynamic size range is extended over that obtainable using visibility alone, without reducing the spatial resolution, and the method is capable of self calibration. The technique employs a pair of two-color coincident beams to create a two fringe sytem. The scattered light signals are processed digitally which permits vigorous validation procedures to be employed. Preliminary results are presented from the application of the technique to vertical annular flow.