A metallic heat transfer tube, in particular for the evaporation of liquids from
pure substances or mixtures on the outside of the tube. Fins are integrally formed
on the outside of the tube. Recesses are arranged in the area of the base of the
primary grooves and extend between the fins. The recesses are in the form of re-entrant
secondary grooves. The mechanical stability of the tube is not negatively influenced
because material is primarily removed from the fin flanks toward the base of the
groove so that the re-entrant secondary grooves are radially open.
