A heat exchanger includes a header and an annular core fluidly connected to the header. The annular core includes an inner diameter, an outer diameter, first flow channels arranged in a first set of layers, and second flow channels arranged in a second set of layers and interleaved with the first flow channels. Each of the first flow channels includes a first inlet, a first outlet, and a first axial region extending between the first inlet and the first outlet. Each of the second flow channels includes a second inlet, a second outlet, and a second axial region extending between the second inlet and the second outlet.