A heat exchange device, comprising: a plurality of flow passages, each flow passage having an inlet and an outlet configured for hot fluid flow in a direction from the inlet to the outlet; and secondary heat transfer elements (132, 134) within and adjacent each flow passage having heat transfer characteristics varying in the direction of the hot fluid flow such that peak metal temperatures, associated creep, and transient thermal stresses are limited to values producing acceptable life of the device; and wherein the heat transfer elements are positioned proximate the inlet and the outlet and gradually transition from straight heat transfer elements at the inlet to shaped heat transfer elements proximate the outlet; wherein proximate the inlet of each flow passage includes a first predetermined number of straight heat transfer elements; characterised in that an intermediate section between the inlet and outlet of the flow passage includes a second predetermined number of straight heat transfer elements and a third predetermined number of shaped heat transfer elements, wherein the second predetermined number is greater than the first predetermined number; and wherein proximate the outlet of the flow passage includes a fourth predetermined number of shaped heat transfer elements greater than the third predetermined number of shaped heat transfer elements; a first section and a second section, each of the first and second sections including flow passages of said plurality of flow passages, and a center manifold disposed between the first and second sections, wherein hot fluid enters the manifold at a first plenum, passes through the first and second sections and exits the center manifold at a second plenum. a plurality of flow passages, each flow passage having an inlet and an outlet configured for hot fluid flow in a direction from the inlet to the outlet; and secondary heat transfer elements (132, 134) within and adjacent each flow passage having heat transfer characteristics varying in the direction of the hot fluid flow such that peak metal temperatures, associated creep, and transient thermal stresses are limited to values producing acceptable life of the device; and wherein the heat transfer elements are positioned proximate the inlet and the outlet and gradually transition from straight heat transfer elements at the inlet to shaped heat transfer elements proximate the outlet; wherein proximate the inlet of each flow passage includes a first predetermined number of straight heat transfer elements; characterised in that an intermediate section between the inlet and outlet of the flow passage includes a second predetermined number of straight heat transfer elements and a third predetermined number of shaped heat transfer elements, wherein the second predetermined number is greater than the first predetermined number; and wherein proximate the inlet of each flow passage includes a first predetermined number of straight heat transfer elements; characterised in that an intermediate section between the inlet and outlet of the flow passage includes a second predetermined number of straight heat transfer elements and a third predetermined number of shaped heat transfer elements, wherein the second predetermined number is greater than the first predetermined number; and wherein proximate the outlet of the flow passage includes a fourth predetermined number of shaped heat transfer elements greater than the third predetermined number of shaped heat transfer elements; a first section and a second section, each of the first and second sections including flow passages of said plurality of flow passages, and