Reactor and reactor unit with hollow fibers

A reactor comprising:

• a rotatably mounted reactor unit having a first chamber and a second chamber, with the first chamber being formed by an interior of a housing and the second chamber being formed by an interior of a plurality of hollow fibers arranged in the housing, and with an axis of rotation of the reactor unit being parallel to an axial direction of the hollow fibers,
• the reactor unit including
• (i) at least two opposed casting compounds in which opposite terminal regions of the hollow fibers are embedded and between which another portion of the hollow fibers extends, with a length of the portion of the hollow fibers extending between the casting compounds being at least 1% greater than a distance between surfaces of the opposed casting compounds so as to provide a bulged or spindle-shaped bundle of the hollow fibers between the casting compounds, and
• (ii) an element that constricts the bulged or spindle-shaped bundle of hollow fibers such that a density of the hollow fibers based on a cross-sectional area of the first chamber is increased in a vicinity of the constriction relative to the density of the hollow fibers without using the element, the element that constricts being located along the bulged or spindle-shaped bundle of hollow fibers between the opposed casting compounds.