Abstract: A rotary heat exchanger characterized in that a spherically coiled heat transfer bypass tube is provided concentrically about a reflux type heat transfer double-tube at a part thereof, the outer tube of the double tube being rotatable, wherein a suction tube is provided around the outer tube within the spherical space defined by the bypass tube, said suction tube incasing screw vanes secured to the outer periphery of the outer tube, whereby convection is induced within the spherical space by the rotation of the outer tube. With the exchanger, good heat exchange efficiency is attainable without scaling.