Abstract: Heat exchanging apparatus for handling solids, slurries, gels, filter cakes, powders, and the like, for continuous indirect heating, drying, cooling or reaction of materials passed through the apparatus. The dryer/heater/cooler apparatus is characterized by a stationary horizontal vessel with a rotary heat exchanger including a tubular shaft on which are mounted a plurality of hollow vertical discs through which a heat exchanging fluid is passed. Material to be treated is admitted to one end of the apparatus housing, transported in an axial direction through the annular space between the rotor discs and the vessel toward the discharge end and discharged through an overflow weir after the desired residence time. Several rotor disc designs are shown and described.