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 . <EOS>