A heat exchanger comprising (a) a hollow, cylindrical roller mounted on its longitudinal axis for rotation about said axis; (b) a manifold positioned in the hollow interior of said roller, said manifold comprising (b1) a central pipe which extends axially along the longitudinal axis of said roller, (b2) a plurality of spoke pipes, wherein said spoke pipes are in communication with said central pipe and with the hollow interior of said roller; (c) a supply means for introducing a heat exchange fluid into said central pipe; and (d) a discharge means for removing said heat exchange fluid from the hollow interior of said roller, so that said heat exchange fluid is sequentially introduced to said central pipe, transferred through said central pipe and then through said spoke pipes, so as to exit said spoke pipes and collide against the inside surface of said roller, thereafter turbulently mixing with the entire mass of said heat exchange fluid contained within the substantially full roller, and thereafter withdrawn from the hollow interior of said roller.
