Abstract: A heat exchanger for transferring heat between an inner and outer medium with a tube bundle for transporting the inner medium. The tube bundle being a plurality of tubes forming concentric rings of tubes. The tubes have angular progressions and are corrugated their entire length; thus adjacent tubes can contact without fatally increasing mechanical tensions. A shell surrounds the tube bundle. An inner medium connector transports the inner medium to and from the tube bundle. An outer medium connector transports the outer medium to and from the shell; the outer medium flowing around the tube bundle inside the shell.