Abstract: An apparatus includes an inlet, an outlet, and a sheet disposed proximate a heat transfer surface, wherein the sheet is oriented in a sheet plane that is displaced from a plane of the heat transfer surface by an angle of at least 10 degrees. The apparatus also includes a plurality of tabs attached to the sheet, the tabs lying in respective tab planes, wherein the tab planes and the sheet plane intersect forming respective intersections. The intersections of the tab planes and the sheet plane are substantially parallel. The intersections of the tab planes and the sheet plane are at an angle of less than 88° to the heat transfer surface, and the plurality of tabs collectively form channels directing a fluid passing from the inlet to the outlet to impinge the heat transfer surface.