Abstract Summary (Max 250 words)
Understanding solid suspension mechanisms in oscillatory baffled reactors (COBRs) has not been extensively explored in the literature; however, it is crucial for transitioning from empirical operation to predictive design. This study addresses the mechanisms of solid suspensions in a NiTech® glass COBR using phase-resolved Particle Image Velocimetry. Experiments used glass beads (dp= 150 and 500 µm) at concentrations of 0.2 % and 1.0 % v/v suspended in calcium chloride solution. The flow conditions were investigated over net Reynolds numbers of 0-20 and oscillatory Reynolds number of 415-1583, achieving different solid-liquid flow regimes (settled bed, moving bed and full suspension). Results show the dispersed phase predominantly attenuates velocity fluctuations relative to single-phase flow. Under identical oscillatory conditions resulting in a settled bed, increased solids concentration enhances turbulence kinetic energy (TKE) via boundary roughening and particle collisions. However, in the fully suspended regime, inertial damping dominates with increased solids concentration, reducing TKE. Larger particle diameters amplify turbulence in settled beds but decrease TKE when fully suspended. To better understand the mechanism governing particle suspension in the COBR, a modified Strouhal number, which compares local and convective acceleration, is proposed to assess the role of local acceleration on solid suspension. The analysis reveals transitions at a critical St of 830–1200 for the settled to moving bed and 2247–4015 for full suspension. A dimensionless parameter (Shields criterion) relating the instantaneous axial and radial velocities to the particle terminal velocity is employed to further elucidate the mechanisms governing solid suspension.
