Abstract: A cylindrical drum exchanges heat between a process fluid sprayed against its inner surface, and a raw product applied to its outer surface. The drum is formed by a thin cylindrical strip which is mounted on two disks. The strip is stiff enough to resist sagging under its own weight. The disks are of smaller diameter than an inner surface of the drum, and a hollow inflatable ring is interposed between each disk and the drum to frictionally connect the drum to the disks for common rotation and form a fluid seal for the ends of the drum. The drum can be removed longitudinally from the disks.