High recovery spiral wound membrane element

In a membrane filtration device of the cylindrical spiral wound type and suitable for filtering a fluid feed mixture under elevated pressure wherein sheet membranes and spacer sheets are tightly wound about a central porous core tube providing separate flow channels for a feed-concentrate mixture and a permeate fluid produced therefrom by means of seals to prevent intermixing of the feed-concentrate and permeate fluids, the improvement which comprises means for providing radial flow for the Feed-concentrate mixture to an extent sufficient to achieve a conversion of 30% or greater while maintaining turbulent or chopped laminer flow, said means including, at least one pair of membrane sheets, separated by a porous spacer sheet, attached longitudinally to, and wound to spiral outwardly about a cylindrical porous core tube and sealed at both lateral edges but unsealed at the terminal edge of the spiral winding to define at least one feed concentrate flow channel extending between the membrane sheets from the porous core tube and the terminal edge of the spiraling membrane sheets, said feed-concentrate flow channel connected to separate conduit means for delivering feed mixture to and discharging concentrate from the feed-concentrate flow channel, and, on each permeate side of said membrane sheets, seals on all edges of all permeate sides of the membrane sheets except for at least one lateral edge to define at least one permeate channel for discharge of permeate from the spirally wound membrane sheets and said permeate channel conducted to conduit means for collection of said permeate.