Inside a two-dimensional model of the louvered Dorfan Impingo panel with transparent front and rear walls the flow regions of filter granules without gas the cross-flow were observed. The white PE beads were used as filter granules. Colored PE beads served as tracers. Filter granules were discharged and circulated to the bed. The flow rate of filter medium was controlled by the belt conveyor. The image processing system was used to record the granular flow. The flow patterns and the quasi-stagnant zones history in the moving granular bed were evaluated. The experiment showed that there exists a fast central moving region (flowing core) of filter granules and two quasi-stagnant zones along the louver walls. The velocity fields in the moving bed in the Dorfan Impingo filter systems were also measured and analyzed. The results indicate that the velocity profiles of filter granules are influenced by the louver geometry. (C) 2000 Elsevier Science Ltd. All rights reserved.