<p>The current invention includes a tube with a helical fin extending from the tube's outer surface The fins and tube are monolithic, or formed of one part, with a channel defined between adjacent fins. The fin has a crest with peaks and depressions formed in the crest. The fin peak includes an indent formed in a side surface, and the indent includes a flank and a base surface. The indent flank intersects the fin peak top, and the indent base surface intersects the fin side wall</p>
