Abstract: A method of making an improved heat transfer tube. The inner surface of the tube has a primary set of fins and an intermediate sets of fins positioned in the areas between the primary fins and at an angle relative to the primary fins. While intermediate fins may be used with primary fins arranged in any pattern, in a preferred embodiment of the inner surface tube design, the intermediate fins are positioned relative to the primary fins to result in a grid-like appearance. Tests show that the performance of tubes having the intermediate fin designs of the present invention is significantly enhanced. A first set of rollers creates the primary and intermediate fin designs on at least one side of a board. A second set of rollers may be used to further enhance the performance.

Abstract: Heat transfer tubes have an exterior surface in contact with a refrigerant and an interior surface defining a path through which a liquid is conveyed in an axial direction of the tube. The exterior surface of the tube has a plurality of fins formed thereon; the interior surface of the tube has a plurality of ridges formed thereon. The fins have an average width v with respect to the axial direction of the tube and a pitch Q with respect to the axial direction of the tube. A channel is provided between adjacent fins, the channels having a channel bottom of length L with respect to the axial direction of the tube. The ridges have a ridge height (e) and a ridge base width (b). The tubes have a ratio of L/v in a range of from 1.22 to 3.40. L is greater than 45% of fin pitch Q, and is preferably between 45% and 75% of fin pitch Q. A ratio of (e.times.L)/b is in a range of from 0.0062 to 0.0165; a ratio of e/b is in a range of from 0.565 to 0.973.

Abstract: Metallic tubes (10,10') for boiling have an outer surface (12) for contacting a refrigerant and an inner surface (14) for contacting a liquid heat transfer medium to be chilled. The outer surface (12) has a plurality of radially outwardly extending helical fins (18); the tube inner surface (14) has a plurality of helical ridges (16). The fins (18) of the outer surface are notched to provide nucleate boiling cavities having pores (30). The fins (18) and notches (N) are so spaced that the pores (30) have an average area less than 0.00009 square inches and a pore density of at least 2000 per square inch on the tube outer surface. The helical ridges (16) on the inner surface have a predetermined ridge height and pitch and are positioned at a predetermined helix angle, the inner surface having a severity factor .PHI. in the range of 0.006 to 0.008.