Abstract: The bed includes a deck having a plurality of openings and side walls defining a trough with the deck. A plenum below the deck supplies air through the openings for fluidizing material in the trough, the openings being arranged to direct air in a manner to establish a predetermined flow pattern for circulating and mixing the material. In one form hereof, the flow direction is transversely of the bed to provide a circular mixing action. In another form, the openings are configured to provide both transverse and horizontal components of flow whereby the material is circulated as it moves downstream through the trough.