Evaluation of using a porous medium approach to simulate flat-sheet membrane bioreactors

Abstract

The porous medium approach has been applied by others to study the global hydrodynamics in hollow-fiber (HF) membrane bioreactors (MBR). This study explores the usability of the porous medium approach for flat-sheet (FS) MBR and introduces a CFD-based numerical calibration of the porous parameters. Two key modeling strategies are suggested to ensure the pressure prediction accuracy: (1) use SST turbulence model incorporated with an intermittency transition model (SSIT); (2) considerate two-phase flow during the calibration. The results showed that SSIT significantly improved the pressure prediction of the flow between two sheets. Also, unlike HF MBR, the gas phase was observed to be non-negligible during the calibration for FS MBR. The numerically calibrated porous parameters were then applied in a three-dimensional simplified model (SPM), where multiple membrane sheets were treated as one porous zone. The SPM was compared with a realistic model (RM), where all membrane sheets were simulated directly. A similar pressure distribution was observed in both models; however, local flow characteristics (i.e., the acceleration of the flow entering the module zone) were not reflected in the SPM. Hence, it is recommended to use the porous medium approach for global hydrodynamics investigation when the local flow characteristics are not of interest. HIGHLIGHTS This study introduces a CFD-based numerical calibration method of the porous parameters.; Unlike the standard calibration method of the porous parameters for HF MBR, this study suggests using two-phase (air-water) flow during the calibration, and the viscous loss term should not be omitted.; This study discusses the capabilities and limitations of the current porous medium approach.;

Keywords

• computational fluid dynamics
• flat-sheet
• hydrodynamics
• mbr
• porous medium