Depending on application and the morphology of membrane cross section, hollow fiber membranes can be used in two different modes: inside-out and outside-in. The former mode means that the feed solution is supplied inside the hollow fiber and the permeate is collected on the outside. While the latter mode implies that feed stream is sent on the outside of the fibers and the filtrate (permeate) is collected inside the fiber.
Fabrication of hollow fibers is a challenging process which requires careful optimization of multiple process parameters and precise manufacturing equipment. One of key elements in hollow fiber spinning process are spinnerets, where coagulation of polymer solution starts upon its contact with bore solution supplied through the central needle to form a hollow part of the fiber.