Patent ID: 8281850

Claim:
A metallic heat exchanger tube ( 1 ) comprising fins ( 2 ) which run in a helical direction around the outside of the tube, are molded integrally from the tube, and are of continuous design; a fin base ( 3 ) which protrudes substantially radially from a tube wall ( 5 ); and a primary groove ( 6 ) located between respectively adjacent fins ( 2 ), wherein an undercut secondary groove ( 8 ) extends in said helical direction and is arranged in the region of a groove base ( 7 ) of the primary groove ( 6 ), said secondary groove ( 8 ) is delimited toward the primary groove ( 6 ) by a pair of mutually opposite material projections ( 9 ) formed from a material of respectively adjacent fin bases ( 3 ), said material projections ( 9 ) extend continuously along the primary groove ( 6 ), the cross-section of the secondary groove ( 8 ) is varied at regular intervals along said helical direction without having an influence on the shape of the fins ( 2 ), and there is a spacing (S) between opposite material projections ( 9 ), characterized in that said spacing (S) is varied at regular intervals, as a result of which local cavities ( 10 ) are formed.