Abstract: A vertically extending heat exchanger is provided in which an elongated dasher is rotatably mounted within an upright cylindrical chamber. The exterior surface of the dasher coacts with the interior surface of the chamber to form a product flow passage. The opposite side of the chamber interior surface is in contact with a heat exchange medium. The dasher is selectively movable longitudinally of the chamber between operative and inoperative modes. When in the operative mode, the dasher is fully assembled within the chamber and is supported at opposite ends by upper and lower endwall assemblies, the latter being mounted, respectively, on the upper and lower exterior end portions of the chamber. The dasher is movable to the inoperative mode when the lower endwall assembly is disassembled from the chamber and the dasher is lowered through the lower end portion of the chamber.