Heat transfer tube and method of manufacture

Abstract

An evaporator heat transfer tube (10) for use in a heat exchanger where heat is transferred between a fluid flowing through the tube and a fluid flowing around the exterior of the tube and where the fluid external to the tube boils during the heat exchange process. The tube has a plurality of helical fins (20) extending around its external surface (13). A pattern of notches (30) extends at an oblique angle (.alpha.) across the fins at intervals about the circumference of the tube. A spike (22) having a flattened distal tip (23) is formed between each pair of adjacent notches. The maximum width (W.sub.t) of the spike at its tip is greater than the width (W.sub.r) of the base portion of the fin and is of a width sufficient to overlap with and contact the distal tips of spikes in adjacent fins on both sides thereof, thus forming reentrant cavities between the adjacent fins and under the overlapping tips. The fins, notches and spikes are formed in the tube by rolling the wall of the tube between a mandrel and, first, a gang of finning disks (63), then, second, a notching wheel (66) and, third, a smooth wheel (67) to flatten the spikes and create the overlapping of spike tips.

Dependencies are inferred from the claim text.