Hybrid flow heat exchangers

A method comprising:

• providing a heat exchanger including:
• a shell surrounding a first fluid plenum, a plurality of flow chamber walls positioned inside the shell, the plurality of flow chamber walls at least partially defining a plurality of first fluid radial flow channels in flow communication with a first fluid inlet and the first fluid plenum, at least partially defining a plurality of second fluid axial flow channels in flow communication with a second fluid inlet, being in thermal communication with and structured to exchange heat between the plurality of first fluid radial flow channels and the plurality of second fluid axial flow channels, and arranged in an array to at least partially define the plurality of first fluid radial flow channels and the plurality of second fluid axial flow channels, and a diffuser positioned inside the shell and including a diffuser surface at least partially defining a diffusion flow path from the first fluid inlet and the plurality of first fluid radial flow channels;
• flowing a first fluid from the first fluid inlet to the diffuser, through the diffuser, from the diffuser to the plurality of first fluid radial flow channels, through the plurality of first fluid radial flow channels, and from the plurality of first fluid radial flow channels to the first fluid plenum;
• and
• flowing a second fluid from the second fluid inlet to the plurality of second fluid axial flow channels and through the plurality of second fluid axial flow channels effective to exchange heat between the plurality of first fluid radial flow channels and the plurality of second fluid axial flow channels.