Flow characteristics and regime transitions in fluidization systems of Group C ⁺ particles

Abstract Fine and ultrafine particles are attractive for fluidized bed reactors because their high surface area benefits catalytic processes, but their cohesive nature complicates regime characterization. Nanoparticle modulation improves the flowability of Group C powders, yet their bubbling to turbulent transition remains unclear. This work systematically characterizes regime transitions of multiple Group C + samples in two‐dimensional and cylindrical beds using high‐frequency pressure‐drop measurements and cross‐sectional solids holdup mapping. Key transition velocities, including turbulent onset ( U c ), characteristic velocity ( U k ), and entrainment velocity ( U se ), are extracted from pressure standard deviations and solids holdup profiles. Group C + particles are shown to form a distinct turbulent regime with lower pressure fluctuations and more uniform solids holdup than Group A beds, consistent with smaller bubbles and a more homogeneous dense phase. Increasing nanoparticle concentration promotes an earlier transition, and the co‐location of transitions from pressure and holdup confirms a framework for regime definition in cohesive systems.