A distributor tube has tube slots in its shell surface transversely of the inflow direction of a fluid into the distributor tube. A casing tube is enclosed by the distributor tube and is divided into flow chambers, each of which is bounded by two annular plates and connected to an inlet sector. A star-shaped volume flow divider is located on the inlet side of the distributor tube as a tube insert, which divides the introduced mass flow rate into partial flow rates for the flow chambers. In another embodiment, the distributor tube encloses a rotationally symmetric pressure distributor, whereby the fluid within the distributor tube encounters equal pressure in the radial and axial flow directions over the inlet length of the distributor tube.