“…For multi-phase flows, hybrid schemes [13] combining PIV and PTV have been used and appear advantageous, however, these methods often employ different types of optical filtering or image segmentation in order to separate different phases in the flow [14,15]. When the velocity is estimated using cross-correlation based algorithms in the presence of poly-dispersed particles, or in the presence of large droplets or bubbles, the measurement is significantly biased towards the velocities of the large particles [16]. Therefore, it is commonly accepted that particle tracking is preferred when a wide range of sizes is present in the flow.…”