Method of manufacturing a high performance heat transfer tube

A method of making an internally ribbed and externally finned heat transfer tube from an unformed tube which comprises the steps of:

• positioning the unformed tube on a mandrel, said mandrel having at least one helically extending depression on its surface;
• displacing the tube wall of the unformed tube by rolling discs over the exterior surface of the tube above the mandrel to press the tube against the mandrel to form at least one helically extending rib on the interior surface of the tubing and to form simultaneously at least one helically extending fin convolution extending around the exterior of the tubing, said external fin convolution having depressed sections located above the internal rib;
• and
• rolling a smooth roller-like disc over the exterior surface of the tube after the external fin convolution and internal rib are formed to bend over the tip portion of the external fin convolution to touch the adjacent convolution at the non-depressed sections of the fin convolution to form subsurface passages which communicate with the surroundings of the tube through openings located at the depressed sections of the fin convolution which are not bent over enough by the smooth disc to touch the adjacent convolution.