Most industrial maize driers are equipped with a multitude of air inlet and outlet ducts located across the drying column. This system enables a good distribution of the drying air flow through the column, but it also creates an obstruction to the grain flow. In order to achieve a better homogeneity of the dried grains, the grain flow around the ducts and the effect of the duct shape on the residence time distribution were studied. Two approaches are used to describe the grain trajectory. Experiments used a transparent device representing a section of an industrial maize drier without air circulation. The first approach involved introducing a layer of artificially coloured particles at the top and measuring the concentration of coloured particles at the outlet, versus time. The second approach was mechanical ; the granular material was considered to be a two dimensional continuous medium. The grain trajectories were recorded using a high speed cine camera (250 pictures/second). It was found that the kinematic two dimensional model gave good prediction of the deformation of a coloured grain layer, and consequently of the residence time dispersion, even though some difference were observed between the experimental and the numerical trajectories.