Abstract: A heat exchanger is disclosed having a tube bundle, intended to internally receive a first fluid, and a shell with an inlet opening at a first end. The shell allows an internal circulation of a second fluid and is arranged to surround the tube bundle. An inner casing to the shell circumscribes the bundle within a heat exchange chamber so that between the casing and the shell an annular region extending in a continuous way along the length of the bundle is defined. The annular region is in fluid communication with the exchange chamber through an outflow opening obtained at a second end of the inner casing where the latter has a rear wall facing an opening of the shell to outlet the second fluid from the heat exchanger. The inlet and outlet openings are in fluid communication by means of the annular region.