Patent ID: 8267163

Claim:
A tube comprising: an outer surface and a spaced apart inner surface coextensive along a longitudinal axis to form a hydraulic area therein; and a plurality of protuberances formed on the inner surface and arranged in a plurality of longitudinal rows, the protuberances including a first radius and a second radius with a planar section disposed therebetween to form a peripheral side of the protuberance, wherein the first radius extends from a peripheral edge of the protuberance, and the second radius terminates at an edge of a substantially planar web integrally formed therewith, wherein the protuberances in one row are longitudinally offset from the protuberances in another row to maintain a substantially constant hydraulic area of the tube along the longitudinal axis, wherein the longitudinal offset of the rows of protuberances positions the peripheral edge of the protuberances in one row in substantial alignment across a width of the tube with the edge of the substantially planar web of the protuberances in another row.