The material to be dried is placed in shelves of trays which are stacked on trolleys and slowly moved through a drying tunnel. Heaters are placed in the air space above the train of trolleys, and internal fans circulate the air around or over the drying material. Some heat is received by radiation from the heating coils and by gas radiation, as well as by conduction through the contact of the goods with the supporting base. These additional heat transfer mechanisms can significantly boost convection in cases where the solids are supported on trays or bands. Likewise in rotary cascading dryers, heat transfer to the raining curtain of particles is not solely by convection with the crossflowing air stream; gas radiation is important, and some heat can be transferred from the hot cylindrical wall as the particles rest in the lower quadrants of the revolving drum.