An inverted heat exchanger device includes an exterior conduit elongated and extending around a center axis between a first end and second end. The exterior conduit including a body having an exterior surface, an interior surface, a center core elongated along the center axis, and plural walls extending between the center core and the interior surface. A first conduit is disposed inside the exterior conduit that includes an inlet, plural core passages, an outlet, and internal manifolds. A first fluid is configured to flow along the first conduit. A second conduit is also disposed inside the exterior conduit. The second conduit includes an inlet, plural core passages, an outlet, and internal manifolds. A second fluid is configured to flow along the second conduit. The plural walls are configured to define the first conduit and the second conduit within the body of the exterior conduit.