Extended Phase‐Doppler System for Characterization of Multiphase Flows

An extended phase‐Doppler anemometry (PDA) system is described, which allows the user to measure the refractive index of spherical particles, in addition to their velocity, diameter and concentration. The extended PDA system incorporates two additional detectors on the receiving side. Each particle generates four Doppler signals. Phase shifts between two pairs of signals are recorded. The ratio between two measured values of phase shifts is a function of the particle refractive index. The phase ratio is shown to be fairly independent of particle velocity or diameter. Calculations based on Mie scattering theory demonstrated the feasibility of the concept. Measurements with monosize droplets of glycerine‐water mixture, covering the refractive index range 1.33–1.44, were used to verify the theoretical predictions. The instrument was also tested with spray flows. It is also shown how the phase‐Doppler technique may be used to distinguish between reflecting and refracting particles. This means that the extended phase‐Doppler system may be employed to recognize particle material, and also to measure locally particle velocities, sizes and concentrations, in a multiphase flow with several transparent dispersed phases and one dispersed phase consisting of reflecting particles.