US Patent 7998254 Membrane module

A helically wound hollow membrane module having a core with a plurality of helically wound layers of semi-permeable hollow fibers wound on the core. The fiber wind angle with respect to any one layer of fibers may be essentially constant along the axial length of the module, except in one or both end or tubesheet regions, where the wind angle may be increased, in at least some of the layers relative to the essentially constant wind angle, to produce an area of decreasing diameter.