A fluid separation assembly (100a, 100b, 100c) comprising: a hollow fiber bundle comprising a plurality of hollow fiber membranes; a first tubesheet and a second tubesheet encapsulating respective ends (136, 138) of the hollow fiber bundle, wherein the first tubesheet includes a first end, a second end, a body portion between the first end and the second end and a plurality of radial through openings formed in the first tubesheet such that the radial through openings of the first tubesheet intersect each of the hollow fiber membranes encapsulated in said first tubesheet; and a housing surrounding the hollow fiber bundle and the first and second tubesheets (154a, 154b), the housing having a feed inlet port for introduction of feed gas, a permeate outlet port for removal of permeate gas, and a non-permeate outlet port for removal of non-permeate gas; wherein the radial through openings are formed around a circumference of the first tubesheet and into the body portion of said first tubesheet and wherein the radial through openings are formed in either: (a) a two opening pattern of rows of two openings that repeat around the circumference of the first tubesheet and radially through the first tubesheet, wherein the two opening pattern is spaced evenly around the circumference of said tubesheet; or (b) a repeating four opening pattern comprising four openings in a substantially square configuration; and wherein the feed inlet port is in flow communication with the radial through openings on the first tubesheet, so that the feed gas can flow into the intersected hollow fiber membranes. a hollow fiber bundle comprising a plurality of hollow fiber membranes; a first tubesheet and a second tubesheet encapsulating respective ends (136, 138) of the hollow fiber bundle, wherein the first tubesheet includes a first end, a second end, a body portion between the first end and the second end and a plurality of radial through openings formed in the first tubesheet such that the radial through openings of the first tubesheet intersect each of the hollow fiber membranes encapsulated in said first tubesheet; and a housing surrounding the hollow fiber bundle and the first and second tubesheets (154a, 154b), the housing having a feed inlet port for introduction of feed gas, a permeate outlet port for removal of permeate gas, and a non-permeate outlet port for removal of non-permeate gas; wherein the radial through openings are formed around a circumference of the first tubesheet and into the body portion of said first tubesheet and wherein the radial through openings are formed in either: (a) a two opening pattern of rows of two openings that repeat around the circumference of the first tubesheet and radially through the first tubesheet, wherein the two opening pattern is spaced evenly around the circumference of said tubesheet; or (b) a repeating four opening pattern comprising four openings in a substantially square configuration; and (a) a two opening pattern of rows of two openings that repeat around the circumference of the first tubesheet and radially through the first tubesheet, wherein the two opening pattern is spaced evenly around the circumference of said tubesheet; or (b) a repeating four opening pattern comprising four openings in a substantially square configuration; and wherein the feed inlet port is in flow communication with the radial through openings on the first tubesheet, so that the feed gas can flow into the intersected hollow fiber membranes.