Development and validation of a model for mitigating particulate fouling in ultrafiltration using water-hammer

Abstract

Membrane fouling is an endemic problem in ultrafiltration used for many applications. Recently water-hammer pulsing has been shown to reduce membrane fouling. Rapid solenoid-valve closure on the retentate or permeate side of a membrane generates a pressure front that propagates and reflects at the system boundaries at the speed-of-sound. However, the mechanism whereby this mitigation occurs is not well-understood. A predictive model is developed for mitigating fouling using pulsed solenoid-valve closure in the ultrafiltration of particulates. The model assumes the boundary-layer flow that develops after the first pressure-front reflection at the upstream boundary causes an enhanced shear stress on the fouled membrane. This increased shear stress typically occurs for less than 0.01 s during each solenoid-valve closure that occurs once every several seconds. However, it has a significant effect on removing the fouling deposits because it is orders-of-magnitude larger than the shear stress of the steady state crossflow velocity. This model correlates with a Coefficient-of-Determination of 0.997 the fractional flux increase for 44 experiments spanning a range of fluxes, foulant concentrations, pressures, and solenoid-valve-closure frequencies for an aqueous whey-protein feed. The fractional flux increase was 10.7%–124% and averaged 51.2%. However, the model indicates that considerably higher flux increases are possible.