Permselective hollow fiber bundle

Claim 1

In a bundle of permselective hollow fibers to be used in pressure driven separations wherein fiber length is controlled to avoid adverse permeability and selection capabilities the improvement consisting of a plurality of radially displaced annular lamellae of said bundle, each lamella comprising a plurality of wraps of helical segments of fiber in which adjacent helical fiber segments are positioned in helices of opposite hand, each said helical segment of fiber within a respective lamella lying at a radial position R f substantially constant over a length of said bundle and with all wraps which comprise any given lamella incorporating helical segments each of whose radial position R f may differ incrementally from one to another segment but with each segment having the same number of turns N per length D; N in each lamella being such that helix paths within each respective lamella are displaced circumferentially and successive traverses of common hand do not overlie one another and thereby substantially avoid helical ridges and each such value of N varies between successive lamellae of increasing median radius.