Tube bundle heat exchanger

A tube bundle heat exchanger having an enveloping outer shell and at least one tubesheet which together define an interior of the tube bundle heat exchanger, comprising

• a tube bundle having a plurality of heat exchanger tubes which are arranged in the interior and through which a first fluid can flow, and which are optionally supported by additional support plates, wherein the heat exchanger tubes have helically circumferential integral fins which are formed on the outside of the tube and have a fin foot, fin flanks and a fin tip, and a channel having a channel bottom is formed between the fins,
• at least one inlet at the outer shell, by way of which a second fluid can be introduced into the interior, and at least one outlet, by way of which the second fluid can be discharged from the interior,
• wherein the at least one tubesheet has openings as passage points, wherein each opening has an inner surface,
• the heat exchanger tubes project at least with their outer fins into the openings of the tubesheet, whereby a joint gap is formed in each case between the inner surface of an opening and the outer fins, located inside the opening, of a heat exchanger tube,
• the heat exchanger tubes, by means of joining material and with the involvement of the outer fins, have a material-bonded connection to the tubesheet, which connection is formed only in a first portion of the opening extending in an axial direction from the end face of a heat exchanger tube, wherein, in this first portion, the joint gap is filled with joining material, so that a second portion of the opening remains, in which the joint gap is not filled with joining material, wherein the heat exchanger tube continues to have outer fins on the outside of the tube in the region of the second portion.