Liquid and liquid/gas flows through spacer filled channels were studied using Particle Imaging Velocimetry (PIV) to pi vide experimental support for velocity distributions obtained from Computational Fluid Dynamics studies available in the literature It is shown that Ply is a suitable technique for measuring velocity profiles in spacer filled channels, although care has to be taken when interpreting the results. PIV measurements were carried out for an entire flow cell (5 cm x 15 cm), a smaller area of roughly 7 mm x 8 mm and for a single spacer cell (2.5 mm x 3 mm) The experimental results show that fluid flow is well distributed across the entire flow cell in the case of single-phase flow The recordings of the single spacer cell showed that liquid flow is mainly parallel to the spacer filaments and therefore the direction of flow changes 90 over the height of the channel Introduction of air bubbles introduced strong local velocity gradients The liquid velocity in two-phase flows is shown to be more unsteady than in the case of single-phase flow, which is advantageous when trying to prevent fouling or concentration polarization. (C) 2010 Elsevier B V. All rights reserved.