Non-invasive observation of flow profiles and polarisation layers in hollow fibre membrane filtration modules using NMR micro-imaging

Abstract Nuclear magnetic resonance (NMR) micro-imaging techniques have been applied to the non-invasive study of flow and polarisation effects in hollow fibre membrane filtration modules. Flow distributions for both feedstock (shell side) and permeate (in the inner lumens of the hollow fibre membranes) have been mapped and the corresponding flow rates measured under different operating conditions. Measured flow velocities, when integrated over the cross section of the modules, yielded volume flow rates in good agreement with directly measured values, confirming the accuracy and reliability of the flow imaging methods employed. The results show evidence for ‘channelling’ of flow in regions of low membrane fibre packing density. Chemical shift selective imaging techniques have been used to visualise the development of oil polarisation layers in the outer surfaces of the fibres during filtration of an oil/water emulsion. Preliminary results are consistent with previous, more invasive, studies of gel polarisation phenomena in membrane filtration modules. They confirm that the hydraulic resistance of the oil layer is a major factor in controlling permeate flux. Attempts to detect flow of the oil layers themselves were unsuccessful, giving an upper limit to the flow rate of the polarisation layers of less than 2 mm/min.