Tube bundle heat exchanger

A tube bundle heat exchanger, comprising:

• an enveloping outer shell;
• at least one tubesheet, the outer shell and the at least one tubesheet together defining an interior of the tube bundle heat exchanger;
• a tube bundle having a plurality of heat exchanger tubes arranged in the interior and through which a first fluid can flow, the heat exchanger tubes having helically circumferential integral fins formed on an outside of the heat exchanger tube and having a fin foot, fin flanks, a fin tip and a channel having a channel bottom formed between the fins;
• at least one inlet at the outer shell for introducing a second fluid into the interior, and at least one outlet at the outer shell for discharging the second fluid from the interior;
• wherein:
• the at least one tubesheet has openings as passage points, each opening having an inner surface,
• the heat exchanger tubes project at least with their outer fins into the openings of the at least one tubesheet, and a joint gap is formed in each case between the inner surface of an opening and the outer fins of a heat exchanger tube located inside the opening,
• the heat exchanger tubes, via joining material and the outer fins, have a material-bonded connection to the at least one tubesheet, the material-bonded connection being formed only in a first portion of the opening extending in an axial direction from an end face of a heat exchanger tube and, in the first portion, the joint gap is filled with joining material so that a second portion of the opening remains, the joint gap not being filled with joining material in the second portion, the heat exchanger tube continuing to have outer fins on the outside of the heat exchanger tube in a region of the second portion.