The hydrodynamic characterisation of an axial-flow membrane module

[摘要] ENGLISH ABSTRACT:The hydrodynamics of a hollow fibre membrane module for the ultrafiltration ofpotable water were investigated. The purpose was to use a hydrodynamic model topredict the permeate flux for modules of various dimensions. Various models wereconsidered, but most of them could not account for important effects such asmacroscopic radial gradients and wet fibre expansion, found in hollow-fibremembrane modules. The Porous Medium Model was found to be a suitable modeland it was used together with a finite element software package, Fastflo, to solve forthe pressure distributions inside the membrane modules and predict permeate flux.The permeability of the membranes was obtained using a combination of numericaland experimental procedures and was found to be 2.3 x 10-13m. A cost analysis wasperformed to find the most economical module dimensions (outer diameter andlength) for any required product flow rate. It was assumed that the cost of the fibresand module housing comprised the capital cost, while the operating cost consisted ofthe pumping energy. A capital recovery factor of 0.3 was used to convert capitalcosts to a yearly cost. It was found that the optimum module dimensions are anouter diameter of between 90mm and 160mm and a length of 0.6m. Finally thepressure distributions on the lumen and shell sides during both cross-flow filtrationand backwash were examined. Shade plots proved useful for identifying possibleareas of stagnant flow, as well as indicating where backwash is the most effective.

[发布机构] Stellenbosch University