Experimental and Machine Learning-Based Investigation of Hydrodynamics in Slurry Bubble Columns

The performance and design of slurry bubble column (SBC) reactors are heavily influenced by key factors such as gas holdup (αG), volumetric mass transfer coefficient (kla), bubble rise velocity (vb), bubble size (db), and mixing behavior. These factors are intricately influenced by possible flow regimes and interactions among liquid-gas and liquid-solid particles. Although numerous experimental studies have investigated the impact of solid particle size, concentration, and flow regime on these parameters, existing models and correlations are often constrained to narrow ranges of conditions. This study bridges the gap by conducting a comprehensive experimental investigation of global αG, vb, kla, and flow regime in SBCs of varying diameters (0.1 and 0.2 m), operated across a varying range of superficial gas velocities (UG). Experiments were performed with different liquid-phase solvents (ethanol and ethylene glycol) and solid particles (glass beads, charcoal, sodium alginate, and CMC) at varying concentrations (1–20%). Experiments revealed that αG reached up to 80% for charcoal and 65% for ethanol-glass bead slurry due to enhanced dispersion and reduced coalescence. In contrast, the CMC showed lower αG due to higher viscosity. kla increased with UG and peaked at low-to-moderate solids, with maximum values observed for 1% charcoal. Transition from homogeneous to heterogeneous flow regimes occurred at 0.12 and 0.05 m/s UG in 0.1 and 0.2 m SBCs, respectively. In addition, this study introduces machine learning (ML) models designed to predict αG, kla, vb, and db with high accuracy across diverse operational conditions. The predicted results closely matched the experimental data with variations of only 5% each for αG, vb, and db and 10% for kla. Additionally, the GUI is developed for the easy prediction of these parameters. The findings offer valuable insights into the relationship between operating conditions and reactor behavior, aiding the design and scale-up of SBC reactors for diverse industrial applications.