Feed spacer for spiral-wound membrane module

A feed spacer for spiral-wound membrane module, comprising:

• a first layer, consisting of a plurality of first filaments with first diameter D1, wherein said plurality of first filaments are substantially in parallel to one another, and are arranged along a first direction;
• and
• a second layer, consisting of a plurality of second filaments with second diameter D2, wherein said plurality of second filaments are substantially in parallel to one another, and are arranged along a second direction;
• said first layer is attached to said second layer, and both said first layer and said second layer bend to the center of the spiral-wound membrane module;
• R is defined as the diameter of the spiral-wound membrane module, R1 is defined as the distance from the inside of said first layer to the center of the spiral-wound membrane module, R2 is defined as the distance from the inside of said second layer to the center of the spiral-wound membrane module, RR is defined as a ratio of R2 to R, 0 <RR <1, R1 is bigger than R2, such that said first layer is an outer layer and said second layer is an inner layer, wherein said first layer is in planar contact with an outer filtration membrane and said second layer is in planar contact with an inner filtration membrane;
• when RR is equal to or bigger than a specific value, D1 is equal to D2 when RR is smaller than said specific value, D1 is smaller than D2, the preferred-ratio of D1 to D2 ranges from 0.79 to 0.85 , so as to balance the shear rate on said inner and outer filtration membranes, and Then to prolong the service life of the spiral-wound membrane module.