A method of making a heat exchanger with a heat exchanger core, the method comprising: defining a space into which the heat exchanger will fit; providing boundary conditions to a topology optimization tool, wherein the boundary conditions comprise at least one of a pressure drop condition, a mass condition, and a thermal energy transfer condition; creating, with the topology optimization tool, a three dimensional design of a heat exchanger core of the heat exchanger based on the boundary conditions, wherein the heat exchanger core comprises: an inlet header; an outlet header; an array of branched channels comprising: a first split at the inlet header; a first juncture at the outlet header, wherein the first split and first juncture are common to an entirety of the array of branched channels; and a plurality of secondary splits and secondary junctures, wherein each secondary split and secondary juncture is situated between the inlet header and the outlet header, wherein a subset of the secondary splits and junctures route fluid through interconnections between fluidly parallel branched channels; determining a tooling pathway of a layer-by-layer additive manufacturing device based on the three dimensional design of the heat exchanger core; and building, with the layer-by-layer additive manufacturing device, the heat exchanger core based on the determined tooling pathway. defining a space into which the heat exchanger will fit; providing boundary conditions to a topology optimization tool, wherein the boundary conditions comprise at least one of a pressure drop condition, a mass condition, and a thermal energy transfer condition; creating, with the topology optimization tool, a three dimensional design of a heat exchanger core of the heat exchanger based on the boundary conditions, wherein the heat exchanger core comprises: an inlet header; an outlet header; an array of branched channels comprising: a first split at the inlet header; a first juncture at the outlet header, wherein the first split and first juncture are common to an entirety of the array of branched channels; and a plurality of secondary splits and secondary junctures, wherein each secondary split and secondary juncture is situated between the inlet header and the outlet header, wherein a subset of the secondary splits and junctures route fluid through interconnections between fluidly parallel branched channels; an inlet header; an outlet header; an array of branched channels comprising: a first split at the inlet header; a first juncture at the outlet header, wherein the first split and first juncture are common to an entirety of the array of branched channels; and a plurality of secondary splits and secondary junctures, wherein each secondary split and secondary juncture is situated between the inlet header and the outlet header, wherein a subset of the secondary splits and junctures route fluid through interconnections between fluidly parallel branched channels; a first split at the inlet header; a first juncture at the outlet header, wherein the first split and first juncture are common to an entirety of the array of branched channels; and a plurality of secondary splits and secondary junctures, wherein each secondary split and secondary juncture is situated between the inlet header and the outlet header, wherein a subset of the secondary splits and junctures route fluid through interconnections between fluidly parallel branched channels; determining a tooling pathway of a layer-by-layer additive manufacturing device based on the three dimensional design of the heat exchanger core; and building, with the layer-by-layer additive manufacturing device, the heat exchanger core based on the determined tooling pathway. <EOS>