Study on the flux distribution in a dead-end outside-in hollow fiber membrane module

•Both analytical and computational approaches were used to assess the geometric effects on the flux distribution.•An original dimensionless number able to determine where the maximum local flux is located.•The connection between the flux distribution and energy utilization was found.•Reducing the permeability and pressure drop in the shell and lumen sides improves the uniformity of the flux distribution.•Fibers with the parabolic-shaped resistance distribution theoretically achieve a completely uniform flux distribution.

In this study, model-based prediction and CFD simulation were performed to systematically study the flux distribution in a dead-end outside-in hollow fiber membrane module. A dimensionless number was proposed to determine where the maximum local flux was located. This number can serve as a guide to avoid deterioration of the flux distribution and enable the key point for cleaning to be determined. The number also indicated that fibers with a specific dimension must be packed with a packing density within the proper corresponding range to avoid poor hydrodynamic conditions in the module. A non-uniformity coefficient N was developed to characterize the flux distribution. The conceptual energy utilization η was suggested as the complement to N. A decrease in N caused by a change in one of the geometric parameters will always accompany an increase in η. Reducing the permeability of the membrane and the pressure drop in both the shell and lumen sides will improve the uniformity of the flux distribution. For the specific hollow fiber membrane module, to ensure better flux distribution and high energy utilization, the following parameters are recommended for the fiber: a length shorter than 2000 mm, a shell void fraction larger than 0.4 and an internal diameter wider than 0.4 mm. Fibers that have the parabolic-shaped membrane resistance distribution will theoretically achieve a completely uniform flux distribution.