HYDRODYNAMIC STUDY OF A HOLLOW FIBER MEMBRANE SYSTEM USING EXPERIMENTALLY AND NUMERICALLY DERIVED SURFACE SHEAR STRESSES

Abstract

Computational fluid dynamics (CFD) models can be used to gain insight into the shear stresses induced by air sparging on submerged hollow fiber membrane bioreactor (MBR) systems. It was found that the average range of shear stresses obtained by the CFD model (0.30-0.60 Pa) and experimentally (0.39-0.69 Pa) were in good agreement, with an error less that 15%. Based on comparison of the cumulative frequency distribution of shear stresses from experiments and simulation, (i) moderate shear stresses (i.e., 50th percentile) were found to be accurately predicted (model: 0.24-0.45 Pa; experimental: 0.25-0.49 Pa) with an error of less than 5%; (ii) high shear stress (i.e., 90th percentile) predictions were much less accurate (model: 0.60-1.23 Pa; experimental: 1.04-1.90 Pa) with an error up to 38%. This was attributed to the fact that the CFD model only considers the two-phase flow (50th percentile) and not the movement of fibers. The latter is likely due to shielding effects or fiber sway, significantly affecting shear stresses at the high end of the distribution. However, this was not accounted for in the model in this study. Despite these deviations, the CFD model in its current state can be used to gain insight into the order of magnitude and shear stress distribution. Inclusion of fiber movement is recommended.