Flow and fouling in a pleated membrane filter

Abstract

Pleated membrane filters are widely used in many applications, and offer significantly better surface area to volume ratios than equal-area unpleated membrane filters. However, their filtration characteristics are markedly inferior to those of equivalent unpleated membrane filters in dead-end filtration. While several hypotheses have been advanced for this, one possibility is that the flow field induced by the pleating leads to spatially non-uniform fouling of the filter, which in turn degrades performance. In this paper we investigate this hypothesis by developing a simplified model for the flow and fouling within a pleated membrane filter. Our model accounts for the pleated membrane geometry (which affects the flow), for porous support layers surrounding the membrane, and for two membrane fouling mechanisms: (i) adsorption of very small particles within membrane pores; and (ii) blocking of entire pores by large particles. We use asymptotic techniques based on the small pleat aspect ratio to solve the model, and we compare solutions to those for the closest-equivalent unpleated filter.

Optimizing the operation of a direct-flow filtration device

“…The main focus of this work was to inves-tigate the influence of the proximity of neighbouring fibres on the flow behaviour and the filtration efficiency. This generalizes the models developed for a single hollow fibre with a blocked end [14] and models where neighbouring fibres are adjacent to one another [15]. The model is able to predict the operating regimes that optimize the uniformity of fluid transport across the whole membrane area, thus maximizing the efficiency of operation.…”

“…The flow was solved for in the asymptotic limits of low permeability and low Reynolds number. Sanaei et al [15] derive a theoretical model for the flow behaviour in a pleated filter, composed of a series of permeable pleated 'fingers'. The impact of pore constriction on filter blocking as a result of this configuration was also explored.…”

“…The impact of pore constriction on filter blocking as a result of this configuration was also explored. In both Hurwitz [14] and Sanaei et al [15], the coupling that results from the flow on the permeate side was not considered. Griffiths et al [16] address the question of how to choose the spatial dependence of the wall permeability to allow for the uniform delivery of solute (nutrient) across the permeable wall in a crossflow device.…”

Modeling and design optimization for pleated membrane filters

“…Second, in this work we only consider one fouling mechanism, while in practice there could be multiple simultaneous mechanisms. It would not be difficult to include multiple fouling mechanisms in our model; for example following the approach of [21]. We note, however, that the more mechanisms we include in our model, the more unknown parameters the model will have and the larger the parameter space to explore.…”

“…[20]), and several authors have proposed models to account for multiple fouling modes. For example, [11], [13], and [21] each proposed different models to account for two distinct fouling mechanisms; and [12] published a model to account for three sequential fouling mechanisms. In this last work, the pore is first constricted by small particles (standard blocking dominates); then, once the pore is sufficiently small, further particles are sieved out (complete blocking dominates); and finally a cake layer is formed that dominates the end stage of the filtration process.…”