Abstract: A heat exchanger has an outer pressure jacket, which is provided with an entry connection for the supply of and an exit connection for the removal of a first heat exchange medium, the jacket surrounding U-shaped, bent pipes through which a second heat exchange medium flows. The pipes are mounted in a pipe supporting floor that is connected with the pressure jacket. The U-shaped pipes are surrounded by a guide jacket which is inwardly radially spaced from the inside wall of the pressure jacket and defines an intermediate annular space therewith. Inner and outer legs of the U-shaped pipes are respectively positioned on one of two concentrical partial circles. The inner pipe legs surround a central pipe which is oriented along the longitudinal axis of the heat exchanger, is connected with the entry connection, is open towards the interior of the heat exchanger, and extends from one end of the heat exchanger to the vicinity of the pipe supporting floor which is located at the other end of the heat exchanger.