Boiling heat transfer pipes

Abstract

A method for producing a boiling heat transfer pipe having in the circumferential wall thereof one or a number of helical or annular cavities under a ceiling wall containing a row of openings regularly spaced at predetermined intervals along the length of the cavities, such method partly including in an arbitrary order the steps of: (a) pressing a set of groove-rolling discs of gradually increased diameters against the outer surface of a blank pipe to form a fin around the circumference of the pipe; (b) pressing a notching gear against the outer side of the fin to cut notches in upper fin portions at predetermined intervals along the length of the fin; (c) pressing a set of splitting roller discs with splitting edges of gradually increased angles substantially along a center line on the outer side of the fin to split and spread apart the upper fin portions in the axial direction of the pipe; and (d) pressing a press roller centrally against the split upper fin portions to form flat side wings on lateral sides of the fin in flush abutting engagement with side wings of adjacent fin portions, covering grooves on opposite sides of the fin to provide cavities having in the ceiling wall thereof a row of openings regularly at predetermined intervals corresponding to the pitch of the notches.