Current Limitations for Predicting Liquid Dispersion in Continuous Flow Bubble Columns Using CFD

Liquid-phase dispersion in a continuous flow bubble column was studied using computational fluid dynamics (CFD) and different combinations of turbulence and biphasic models. The results were compared with the experimental data obtained by the stimulus-response method in an air-water pilot-scale bubble column (2 m tall, 0.234 m internal diameter). Two flow combinations were examined: high flow rates of 3.2 m³ h⁻¹ and 4.5 m³ h⁻¹ and low flow rates of 1.98 m³ h⁻¹ and 0.954 m³ h⁻¹ for water and air, respectively. The objective was to evaluate commercial CFD 16.1 software to predict flow behavior beyond macroscale parameters such as hold-up or mixing time. The turbulence models that best replicated the experimental tracer dispersion were large eddy simulation-type models: scale-adaptive simulation (SAS) and shear stress transport-SAS. The simulations qualitatively predicted the tracer concentration with time but were unable to reveal the small-scale perturbations in the biphasic system. The predicted tracer residence time was double or triple the measured times for low and high flow, respectively.