A heat exchanger system (1100) includes a first heat exchanger assembly (200) including a plurality of airfoil members (202) circumferentially spaced in a flow stream (156) of an annular duct (150). Each airfoil member (202) including a radially inner end (204) and a radially outer end (206) and a first internal flowpath (208) configured to channel a flow of cooled fluid therethrough. The heat exchanger assembly includes a second heat exchanger assembly (300) including a plurality of fin members extending proximate the flow stream (156) and a second internal flowpath (306) configured to channel a flow of cooled fluid therethrough. The heat exchanger assembly includes a header system (1108) including a conduit path configured to couple the first heat exchanger assembly (200) and the second heat exchanger assembly (300) in flow communication. The header system (1108) includes an inlet connection configured to receive a flow of hot fluid from thermal loads (1102) and an outlet connection configured to direct cooled fluid to thermal loads (1102).