A feature of this type of apparatuses is that the tubes are rigidly connected to the tube sheets and welded to the shell. Therefore the possibility of mutual displacement in the tube and shell and tube is excluded. Tubes must be placed so that the gap between the inner wall of the shell and the surface of the envelope tube bundle is minimized; otherwise significant portion of the coolant can bypass the main heat exchanger surface. To reduce the amount of coolant passing between the tube bundle and the housing, this space is set with special fillers, for example welded to the shell longitudinal strips or blind pipes which do not pass through the tube sheets and can be arranged directly at the inner surface of the shell. If the sectional area of the tube space (number and diameter of the pipes) is selected, the result of calculation determined the heat transfer coefficient and a heat transfer surface on which the calculated length of the tube bundle. The latter can be greater than the length of commercially available tubes. Therefore multiport (in tube space) devices with longitudinal bulkheads in the distribution chamber are used. Industry produces two-, four- and six-way heat exchangers of longitudinal baffle rigid structure.