INTERFERENCE PATTERNS FOR SPIRAL-WOUND ELEMENTS
Embodiments of the present invention provide for the deposition of spacing elements on both opposing surfaces of either an entire folded membrane sheet or portions thereof in combination with features deposited on portions of the same sheet to create spacing geometries not otherwise achievable.
1 . A membrane for use in a spiral wound filtration element, comprising a first leaf and a second leaf, where each leaf has an active surface with a plurality of protrusions disposed on the active surface, the first leaf and second leaf disposed with the active surfaces facing each other, the protrusions shaped and disposed on the active surfaces such that the protrusions on the first leaf are in contact with the protrusions on the second leaf, with the protrusions on the first leaf separated from the active surface of the second leaf by the protrusions on the second leaf.
2 . A membrane as in claim 3 , comprising a sheet of membrane material folded along a fold line, wherein the first leaf comprises a first portion of the sheet; and the second leaf comprises a second portion of the sheet, separated from the first portion by a fold line.
3 . A membrane as in claim 1 , wherein the protrusions comprise a plurality of line-shaped protrusions, where the line-shaped protrusions are disposed parallel to each other and separated from each other in all planar directions on the surface of the corresponding leaf; and wherein the line-shaped protrusions are disposed on the surface at an angle other than 90 degrees from the feed edge of the corresponding leaf such that the line-shaped protrusions on the first leaf contact the line-shaped protrusions on the second leaf at their intersections.
4 . A membrane as in claim 3 , wherein the angle is between 40 and 85 degrees, or between 100 and 135 degrees.
5 . A membrane as in claim 3 , wherein the protrusions protrude from the surface of each leaf by at least 0.065 mm but not more than 0.4 mm.
6 . A membrane as in claim 1 , wherein the protrusions comprise a plurality of curved features, configured such that the curved feature on the first leaf will intersect the curved features on the second leaf at an angle other than 0 degrees when the membrane is spirally wound.
7 . A membrane as in claim 3 , wherein the line-shaped protrusions extend across the entire width of the corresponding leaf.
8 . A membrane as in claim 3 , wherein the line-shaped protrusions extend across less than the entire width of the corresponding leaf.
9 . A membrane as in claim 8 wherein the line-shaped protrusions are at least 20 mm long in the axial dimension and the spacing between line segments is less than the length of the line segments.
10 . A membrane as in claim 1 , wherein the protrusions are disposed in a first region of the first leaf, and in a first region of the second leaf, and further comprising a plurality of flow protrusions disposed (a) on the active surface of the first leaf other than in the first region of the first leaf, (b) on the active surface of the second leaf other than in the first region of the second leaf, or (c) both, wherein the flow protrusions have a height about equal to the sum of the height of the protrusions in the first region of the first leaf and the height of the protrusions in the first region of the second leaf, and wherein flow protrusions on one leaf are not in contact with those on the other leaf.
11 . A membrane as in claim 10 , wherein the flow protrusions are disposed on the first leaf and not on the second leaf.
12 . A membrane as in claim 8 , wherein the line-shaped protrusions are disposed in regions proximal the feed and reject edges of the corresponding leaf, and further comprising a plurality of flow protrusions disposed (a) on the active surface of the first leaf in regions other than those occupied by the line-shaped protrusions, (b) on the active surface of the second leaf in regions other than those occupied by the line-shaped protrusions, or (c) both, wherein the flow protrusions have a height about equal to the sum of the height of the line-shaped protrusions on the first leaf and the height of the line-shaped protrusions on the second leaf; and wherein the flow protrusions on one leaf do not contact those on the other leaf when the element is spiral wound.
13 . A membrane as in claim 12 , wherein the flow protrusions are disposed on the first leaf and not on the second leaf.
14 . A method of making a membrane as in claim 3 , comprising providing a first leaf and a second leaf, each having an active surface;
placing a plurality of protrusions on the active surface of each leaf;
placing the active surface of the first leaf adjacent to the active surface of the second leaf, separated by the protrusions;
wherein the protrusions are shaped and disposed on the active surfaces such that the protrusions on the first leaf are in contact with the protrusions on the second leaf, with the protrusions on the first leaf separated from the active surface of the second leaf by the protrusions on the second leaf.
15 . A method as in claim 14 , wherein providing a first leaf and a second leaf comprises providing a sheet separated into a first leaf and a second leaf by a fold line; and wherein placing the active surface of the first leaf adjacent to the active surface of the second leaf comprises folding the sheet along the fold line.
16 . A filtration element comprising a membrane as in claim 3 , spirally wound around a center tube.