In small, dryers the material is placed on trays, which slide into the drying cabinet, while in large installations the interior may be designed for the wheeling in of trolleys containing the trays.
The simplest form of heating places the sources of heat (e. g. a steam coil or electrical coil) at floor level and relies on natural convection. Fans provide a forced circulation of air across the trays. Air flows in axle direction over each shelf in turn.
The wet material spread directly on the shallow trays resting on the shelves. Electrical elements (heater) or steam heated pipes are positioned so that air is periodically reheated after it has cooled by passage over the wet material on one shelf before it passes over the material on the next shelf. Tray dryer is a type of Fixed Bed Dryers i.e., the bed of the material to be dried is stationary.