An experimental aerodynamic study was carried out in order to obtain a better understanding of the heterogeneous treatment observed during the forced convection cooling of products conditioned in bins. Velocity and turbulence intensity were measured at different depths inside a bin of spherical products. Airflow was far from being a plug flow: the air was introduced at the centre of the inlet wall and progressively redistributed over the width of the bin, generating two lateral back-mixings. From the fourth row of spheres onwards, the air flowed preferentially in the empty space between the bin in question and the one above, i.e. above the products, and between the products and the bin walls. The turbulence generated behind the products increased turbulence intensity by up to 60%, The study gives a clearer explanation (detailed in Part II) of the heat transfer phenomena observed experimentally. Changes in bin geometry are recommended to improve airflow around the products.