A gas turbine engine comprising: a compressor section; a combustor section; a turbine section; and a heat exchanger, the heat exchanger comprising: a first additively manufactured manifold that includes a first inlet feed manifold and a first outlet feed manifold; a second additively manufactured manifold that includes a second inlet feed manifold and a second outlet feed manifold; and a plurality of tubes fluidly connecting the first inlet feed manifold to the first outlet feed manifold, wherein the tubes are round and/or circular in cross-section, wherein each of the tubes has a diameter that has a first value between 0.03 inches and 0.3 inches (762 micrometers and 7,620 micrometers), wherein each of the tubes has a wall thickness that has a second value between 0.001 inches and 0.015 inches (25 micrometers and 381 micrometers), wherein the plurality of tubes each include a wall, wherein a first fluid is conveyed from the first inlet feed manifold to the first outlet feed manifold within an interior of the tubes, the interior defined relative to the wall of each of the tubes, and wherein a second fluid is conveyed from the second inlet feed manifold to the second outlet feed manifold around an exterior of the tubes, the exterior defined relative to the wall of each of the tubes. a compressor section; a combustor section; a turbine section; and a heat exchanger, the heat exchanger comprising: a first additively manufactured manifold that includes a first inlet feed manifold and a first outlet feed manifold; a second additively manufactured manifold that includes a second inlet feed manifold and a second outlet feed manifold; and a plurality of tubes fluidly connecting the first inlet feed manifold to the first outlet feed manifold, wherein the tubes are round and/or circular in cross-section, wherein each of the tubes has a diameter that has a first value between 0.03 inches and 0.3 inches (762 micrometers and 7,620 micrometers), wherein each of the tubes has a wall thickness that has a second value between 0.001 inches and 0.015 inches (25 micrometers and 381 micrometers), wherein the plurality of tubes each include a wall, wherein a first fluid is conveyed from the first inlet feed manifold to the first outlet feed manifold within an interior of the tubes, the interior defined relative to the wall of each of the tubes, and wherein a second fluid is conveyed from the second inlet feed manifold to the second outlet feed manifold around an exterior of the tubes, the exterior defined relative to the wall of each of the tubes. a first additively manufactured manifold that includes a first inlet feed manifold and a first outlet feed manifold; a second additively manufactured manifold that includes a second inlet feed manifold and a second outlet feed manifold; and a plurality of tubes fluidly connecting the first inlet feed manifold to the first outlet feed manifold, wherein the tubes are round and/or circular in cross-section, wherein each of the tubes has a diameter that has a first value between 0.03 inches and 0.3 inches (762 micrometers and 7,620 micrometers), wherein each of the tubes has a wall thickness that has a second value between 0.001 inches and 0.015 inches (25 micrometers and 381 micrometers), wherein the plurality of tubes each include a wall, wherein a first fluid is conveyed from the first inlet feed manifold to the first outlet feed manifold within an interior of the tubes, the interior defined relative to the wall of each of the tubes, and wherein a second fluid is conveyed from the second inlet feed manifold to the second outlet feed manifold around an exterior of the tubes, the exterior defined relative to the wall of each of the tubes.