High-speed micro-focusing shadowgraphy measuring particle velocities in densely-seeded particle-laden flows

Abstract: High-speed micro-focusing shadowgraph velocimetry (µ-PSV) has been developed to measure particle velocity and concentration under high-loading conditions, with a particle volume fraction, Φv,p, of O(10−1) in the four-way coupling regime. A high-speed camera operating at 10 kHz, coupled with the earlier developed µ-PSV setup, is used to study the particle dynamics at the jet exit for an impulsively-seeded, particle-laden flow into an otherwise continuous jet in an isothermal lab-scale model of a drop-tube reactor. A spatial resolution of 3 µm/pixel and a narrow depth of field of approximately ± 0.3 mm can be achieved with the current configuration, resulting in 15 pairs of particle tracks for a single particle and up to around 35 particles identified in a single image view (2.9 mm × 3.8 mm). This benefits studies of detailed particle phenomena, such as inter-particle collision, particle clustering, and pairing, with high temporal and spatial resolution, as demonstrated. Both particle counting and image intensity have been found to be sensitive to Φv,p, which gives confidence to use this technique, despite further work being needed to resolve cluster motion and calibrate measurements of Φv,p for providing absolute values. The complex flow dynamics of this system, including an initial rapid rise, a plateau, and a zone of high variability in the velocity profile, have also been revealed. Keywords: Particle-laden jet, two-phase flow, shadowgraph, particle image/tracking velocimetry