Characterization of phase detection optical probes for the measurement of the dispersed phase parameters in sprays

In order to be able to investigate the characteristics and the spatial evolution of dense sprays produced by coaxial injectors for instance, a measuring technique based on a phase detection optical probe has been developed. Conical optical probes have previously been successfully used in bubbly flows. Aside local concentration, the velocity of gas inclusions was deduced from the analysis of the dewetting time, and, combined with the gas residence time, the bubble size was obtained. Here, it is shown that this technique can also be helpful for the measurements of drop characteristics in dense sprays. Using controlled conditions in terms of drop size, velocity and trajectory, it is demonstrated that for drops above 30 μm in diameter, the velocity and size are evaluated with an uncertainty less than about 15% including variations in the impact conditions. An adapted signal processing has been developed which is shown to be weakly sensitive to the various criteria introduced. When applied to sprays generated by a two-dimensional gas–liquid mixing layer, volumetric fluxes measured by the probe are shown to agree within 15% with a sampling technique. To illustrate the capability of this fairly objective tool, some results are provided and analyzed for the drop velocities and chords as well as for the concentration and the interfacial area density in the near field of dense sprays with a wide size distribution.