A heat exchanger includes a heat exchanger body having a first end and a second end opposed to the first end along a flow axis. A plurality of flow channels is defined in the heat exchanger body extending axially with respect to the flow axis. A first set of the flow channels forms a first flow circuit and a second set of the flow channels forms a second flow circuit that is in fluid isolation from the first flow circuit. Each flow channel is fluidly isolated from the other flow channels. The flow channels all conform to a curvilinear profile.