Hydrodynamic analysis and residence time distribution modeling of a micro liquid–solid fluidized bed

Micro-fluidized beds (MFBs) are increasingly studied for process intensification due to their compact geometry and high surface-to-volume ratio, which enhance mixing and improve mass and heat transfer. This study examines the hydrodynamic behavior of a liquid–solid MFB through an experimental analysis of bed expansion and residence time distribution (RTD). Experiments were conducted in a miniaturized fluidized bed reactor (0.14 m in height, 0.018 m in internal diameter), using 0.002 m diameter glass beads fluidized with water at 20 ± 2 °C. The minimum fluidization velocity, Umf, was determined by analyzing the bed expansion ratio (H−H0H0) as a function of superficial fluid velocity, U. Bed expansion results indicate that the miniaturized system maintains hydrodynamic consistency with larger scales, as the measured Umf differed by less than 3% from values obtained for conventional-scale systems at equivalent column-to-bed height ratios. The Umf predicted by the Coltters and Rivas correlation showed an average relative deviation of 26%, whereas the Ergun equation provided more accurate predictions, with deviations not exceeding 7%. RTD measurements reveal non-ideal flow behavior, well captured by the plug flow–dispersion model for porosities ε=0.43−0.74. At higher porosity (ε=0.84), enhanced dispersion and possible structural heterogeneities reduce model accuracy, indicating a transition toward a more heterogeneous hydrodynamic regime.