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A machine may produce a tube having textured internal and external surfaces in a single operation. Inner and outer knurling tools may form the textured surfaces. The texturing of the internal and external surfaces may be helical patterns of ribs and grooves. The height of the ribs formed in the inte

A machine may produce a tube having textured internal and external surfaces in a single operation. Inner and outer knurling tools may form the textured surfaces. The texturing of the internal and external surfaces may be helical patterns of ribs and grooves. The height of the ribs formed in the internal and external surfaces may be less than about 35 mils. The angles of the patterns relative to a longitudinal axis of the tube may be less than about 45°. The angle of the helical pattern allows textured tubes to be used as heat exchanger elements wherein flow is directed substantially coaxial to the longitudinal axes of the tubes. The helical pattern formed in the external surface may be oriented in a right hand or left hand helical orientation. Similarly, the helical pattern formed in the internal surface may be oriented in a right hand or left hand orientation.

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1. A method of producing an extended surface area heat exchanger element with a texturing machine, comprising:forming a helical pattern of grooves in an outer surface of a tube with two or more outer knurling tools radially displaced about the tube;forming a helical pattern of grooves in an inner su

1. A method of producing an extended surface area heat exchanger element with a texturing machine, comprising:forming a helical pattern of grooves in an outer surface of a tube with two or more outer knurling tools radially displaced about the tube;forming a helical pattern of grooves in an inner surface of the tube with an inner knurling tool simultaneously with the formation of the helical pattern in the outer surface of the tube; andwherein the texturing machine leaves an un-textured surface near a first end of the tube. 2. The method of claim 1, wherein a depth of the grooves formed in the outer surface is less than about 0.035 inches and greater than about 0.004 inches. 3. The method of claim 1, wherein a depth of the grooves formed in the outer surface is less than about 0.025 inches and greater than about 0.004 inches. 4. The method of claim 1, wherein a depth of the grooves formed in the inner surface is less than about 0.035 inches and greater than about 0.004 inches. 5. The method of claim 1, wherein a depth of the grooves formed in the inner surface is less than about 0.025 inches and greater than about 0.004 inches. 6. The method of claim 1, wherein a depth of the grooves formed in the inner surface is less than about 0.020 inches and greater than about 0.004 inches. 7. The method of claim 1, further comprising pointing a first section of the tube near a first end to produce a cylindrical end portion and a reducing taper that transitions a diameter of the tube from a large diameter to a smaller diameter of the cylindrical end portion. 8. The method of claim 7, wherein pointing the first section of the tube comprises forcing the first end of the tube into a tube-pointing die, the tube-pointing die comprising a frustro-conical surface and an end having a cylindrical section configured to form the cylindrical end portion. 9. The method of claim 7, further comprising pointing a second section of the tube near a second end. 10. The method of claim 1, wherein an orientation of the helical pattern in the outer surface is in a right-hand helical orientation. 11. The method of claim 10, wherein an orientation of the helical pattern in the inner surface is in a right-hand helical orientation. 12. The method of claim 10, wherein an orientation of the helical pattern in the inner surface is in a left-hand helical orientation. 13. The method of claim 1, wherein an orientation of the helical pattern in the outer surface is in a left-hand helical orientation. 14. The method of claim 13, wherein an orientation of the helical pattern in the inner surface is in a right-hand helical orientation. 15. The method of claim 13, wherein an orientation of the helical pattern in the inner surface is in a left-hand helical orientation. 16. The method of claim 1, wherein the texturing machine leaves an un-textured surface near a second end of the tube. 17. The method of claim 1, wherein the angle of the pattern in the outer surface is greater than about 2° relative to the longitudinal axis of the tube. 18. The method of claim 1, wherein the angle of the pattern in the inner surface is greater than about 10° relative to the longitudinal axis of the tube. 19. The method of claim 1, wherein the angle of the pattern in the inner surface is about 30° relative to the longitudinal axis of the tube. 20. The method of claim 1, wherein forming the grooves in the inner surface and forming the grooves in the outer surface produces crosshatched texturing in the inner surface and in the outer surface of the tube. 21. The method of claim 1, wherein at least one of the outer knurling tools is configured to be canted at an angle from about 1.5° to about 5° relative to the tube. 22. A method of forming a tube having a textured inner surface and a textured outer surface, comprising:placing the tube in a texturing machine so that a portion of the inner surface contacts an inner knurling tool;placing two or more outer knurling tools again st an outer surface of the tube to press the inner surface of the tube against the inner knurling tool, wherein the outer knurling tools are radially displaced about the tube;forming a helical pattern of grooves in the inner surface of the tube, the pattern of grooves corresponding to a pattern of ribs in the inner knurling tool;forming a helical pattern of grooves in the outer surface of the tube, the pattern of grooves corresponding to a pattern of ribs in the outer knurling tools; andstopping formation of grooves in the outer surface before reaching an end of the tube. 23. The method of claim 22, further comprising canting the outer knurling tools relative to a longitudinal axis of the tube before placing the outer knurling tools against the outer surface of the tube. 24. The method of claim 23, wherein at least one of the outer knurling tools is adjustable relative to the longitudinal axis of the tube in a range from about 1.5° to about 5°. 25. The method of claim 22, wherein a depth of the grooves formed in the inner surface is less than about 0.035 inches. 26. The method of claim 22, wherein a depth of the grooves formed in the inner surface is less than about 0.025 inches. 27. The method of claim 22, wherein a depth of the grooves formed in the inner surface is less than about 0.020 inches. 28. The method of claim 22, wherein an angle of the pattern of grooves formed in the inner surface is less than about 45° with respect to a longitudinal axis of the tube. 29. The method of claim 22, wherein the angle of the pattern of grooves formed in the inner surface is greater than about 10° relative to a longitudinal axis of the tube. 30. The method of claim 22, wherein an angle of the pattern of grooves formed in the inner surface is about 30° with respect to a longitudinal axis of the tube. 31. The method of claim 22, wherein an angle of the pattern of grooves formed in the outer surface is less than about 45° with respect to a longitudinal axis of the tube. 32. The method of claim 22, wherein the angle of the pattern in the outer surface is greater than about 2° relative to the longitudinal axis of the tube. 33. The method of claim 22, wherein placing the outer knurling tools against the outer surface comprises leaving an end portion of the tube beyond a knurling surface of the outer knurling tools so that the end portion will not be textured by the outer knurling tools. 34. The method of claim 22, wherein an orientation of the helical pattern in the outer surface is in a right-hand helical orientation. 35. The method of claim 34, wherein an orientation of the helical pattern in the inner surface is in a right-hand helical orientation. 36. The method of claim 34, wherein an orientation of the helical pattern in the inner surface is in a left-hand helical orientation. 37. The method of claim 22, wherein an orientation of the helical pattern in the outer surface is in a left-hand helical orientation. 38. The method of claim 37, wherein an orientation of the helical pattern in the inner surface is in a right-hand helical orientation. 39. The method of claim 37, wherein an orientation of the helical pattern in the inner surface is in a left-hand helical orientation. 40. The method of claim 22, wherein forming grooves in the inner surface and forming grooves in the outer surface produces a crosshatched texturing pattern in the inner and outer surfaces. 41. The method of claim 22, further comprising forming a reduced diameter cylindrical section at each end of the tube. 42. A method of forming a tube having a textured inner surface and a textured outer surface, comprising:placing a tube in a texturing machine, so that a portion of the inner surface contacts an inner knurling tool, and wherein the inner knurling tool is rotatively mounted to a mandrel;placing two or more outer knurling tools against an outer surface of the tube to press the inner surface of the tube against the inner knurling tool, wherein the outer knurling tools are radially displaced about the tube;forming a helical pattern of grooves in the inner surface of the tube, the pattern of grooves corresponding to a pattern of ribs in the inner knurling tool;forming a helical pattern of grooves in the outer surface of the tube, the pattern of grooves corresponding to a pattern of ribs in the outer knurling tools; andwherein the texturing machine leaves an un-textured surface near a first end of the tube. 43. The method of claim 42, wherein the mandrel supports a portion of the tube. 44. The method of claim 42, wherein the mandrel is a rod. 45. The method of claim 42, wherein the inner knurling tool is mounted proximate a first end of the mandrel. 46. The method of claim 42, wherein the texturing machine further comprises a drive configured to rotate the outer knurling tool. 47. The method of claim 42, wherein the texturing machine further comprises positioners, and wherein each positioner is configured to adjust the position of one of the outer knurling tools relative to the tube. 48. The method of claim 42, further comprising pointing a first section of the tube near a first end to produce a cylindrical end portion and a reducing taper that transitions a diameter of the tube from a large diameter to a smaller diameter of the cylindrical end portion. 49. The method of claim 42, wherein the texturing machine leaves an un-textured surface near a second end of the tube. 50. The method of claim 42, wherein forming the grooves in the inner surface and forming the grooves in the outer surface produces crosshatched texturing in the inner surface and in the outer surface of the tube. 51. The method of claim 42, further comprising driving the tube through the texturing machine by rotation of the outer knurling tools against the tube. 52. The method of claim 51, wherein at least one of the outer knurling tools is canted at an angle that is greater than about 0.5° and less than about 4.5° relative to a longitudinal axis of the tube. 53. The method of claim 9, wherein pointing the second section of the tube comprises forcing the second end of the tube into a tube-pointing die, the tube-pointing die comprising a frustro-conical surface and an end having a cylindrical section configured to form the cylindrical end portion. 54. The method of claim 22, further comprising pointing a first section of the tube near a first end to produce a cylindrical end portion and a reducing taper that transitions a diameter of the tube from a large diameter to a smaller diameter of the cylindrical end portion. 55. The method of claim 48, further comprising pointing a second section of the tube near a second end to produce a cylindrical end portion and a reducing taper that transitions a diameter of the tube from a large diameter to a smaller diameter of the cylindrical end portion.