Scattering imaging to measure size and velocity of small particles in dense particle systems

A new scheme for GSI out-of-focus technique able to simultaneously measure size and velocity of droplets is presented and the basic principles discussed. The new approach, GSI-V, is based on a single CCD and a double laser pulse with crossed polarization. In the proposed system a slit is used in front of the detection optics to reduce large circular out-offocus images to thin strings. This, together with the crossed polarizations of the laser pulses, permit the application of GSI-V to moderately dense droplets systems. Measurements of size and velocity of droplets in a calibrate spray of water are reported. A theoretical analysis concerning the application of the out-of-focus method to small droplets is also outlined. In dedicated experiments GSI approach was applied successfully to binary evaporating droplets as small as 7 µm.