An apparatus providing enhanced heat transfer, the apparatus comprising: an inlet; an outlet; a heat transfer surface; a sheet disposed proximate said heat transfer surface, the sheet (1; 15) being oriented in a sheet (1; 15) plane that is displaced from a plane of the heat transfer surface by an angle of at least 10 degrees; and a plurality of tabs attached to the sheet (1; 15), the tabs lying in respective tab planes, wherein: the tab planes and the sheet (1; 15) plane intersect forming respective intersections; the intersections of the tab planes and the sheet (1; 15) plane are substantially parallel; the intersections of the tab planes and the sheet (1; 15) plane are at an angle of less than 88° to the heat transfer surface; and the plurality of tabs collectively forms channels directing a fluid passing from the inlet to the outlet to impinge the heat transfer surface, characterized in that the sheet (1; 15) provides wall sections that are folded by 180° around a back of the sheet with forming new edges and that the tabs are formed by cutting or blanking the sheet (1; 15) having edges along lines and by folding portions of the sheets at least 10° upward, the intersections between the respective tab plane and the sheet (1; 15) plane are the lines where the sheet (1; 15) is folded to form the tabs with the edge of the formed sheet abuts said heat transfer surface and gaps lie intermittently between the formed sheet (1; 15) and the heat transfer surface. an inlet; an outlet; a heat transfer surface; a sheet disposed proximate said heat transfer surface, the sheet (1; 15) being oriented in a sheet (1; 15) plane that is displaced from a plane of the heat transfer surface by an angle of at least 10 degrees; and a plurality of tabs attached to the sheet (1; 15), the tabs lying in respective tab planes, wherein: the tab planes and the sheet (1; 15) plane intersect forming respective intersections; the intersections of the tab planes and the sheet (1; 15) plane are substantially parallel; the intersections of the tab planes and the sheet (1; 15) plane are at an angle of less than 88° to the heat transfer surface; and the plurality of tabs collectively forms channels directing a fluid passing from the inlet to the outlet to impinge the heat transfer surface, characterized in that the sheet (1; 15) provides wall sections that are folded by 180° around a back of the sheet with forming new edges and that the tabs are formed by cutting or blanking the sheet (1; 15) having edges along lines and by folding portions of the sheets at least 10° upward, the intersections between the respective tab plane and the sheet (1; 15) plane are the lines where the sheet (1; 15) is folded to form the tabs with the edge of the formed sheet abuts said heat transfer surface and gaps lie intermittently between the formed sheet (1; 15) and the heat transfer surface. the tab planes and the sheet (1; 15) plane intersect forming respective intersections; the intersections of the tab planes and the sheet (1; 15) plane are substantially parallel; the intersections of the tab planes and the sheet (1; 15) plane are at an angle of less than 88° to the heat transfer surface; and the plurality of tabs collectively forms channels directing a fluid passing from the inlet to the outlet to impinge the heat transfer surface, characterized in that the sheet (1; 15) provides wall sections that are folded by 180° around a back of the sheet with forming new edges and that the tabs are formed by cutting or blanking the sheet (1; 15) having edges along lines and by folding portions of the sheets at least 10° upward, the intersections between the respective tab plane and the sheet (1; 15) plane are the lines where the sheet (1; 15) is folded to form the tabs with the edge of the formed sheet abuts said heat transfer surface and gaps lie intermittently between the formed sheet (1; 15) and the heat transfer surface.