A heat exchanger comprising: an external casing comprising: a first inlet; a first outlet in fluid communication with the first inlet; a second inlet; and a second outlet in fluid communication with the second inlet; and a core disposed within the external casing, the core comprising: an inlet header integrally formed with and fluidly connected to the first inlet; an outlet header integrally formed with and fluidly connected to the first outlet; and an array of branched channels connecting the first inlet and to the first outlet, wherein the external casing and an exterior surface of the array of branched channels define a fluidic passage between the second inlet and the second outlet, wherein the array of branched channels comprises: 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; characterized by a secondary branching structure including one or more secondary splits and one or more secondary junctures, wherein the secondary split and secondary juncture are situated between the inlet header and the outlet header, and wherein a subset of the secondary splits and secondary junctures route fluid through interconnections between fluidly parallel branched channels; wherein the array of branched channels is pattern-less, such that there are no repeating patterns of branched channels, splits, and junctures within the core and the branched channels have varying shapes, sizes, diameters, and outer boundary lengths throughout the array. a first inlet; a first outlet in fluid communication with the first inlet; a second inlet; and a second outlet in fluid communication with the second inlet; and a core disposed within the external casing, the core comprising: an inlet header integrally formed with and fluidly connected to the first inlet; an outlet header integrally formed with and fluidly connected to the first outlet; and an array of branched channels connecting the first inlet and to the first outlet, wherein the external casing and an exterior surface of the array of branched channels define a fluidic passage between the second inlet and the second outlet, wherein the array of branched channels comprises: 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; characterized by a secondary branching structure including one or more secondary splits and one or more secondary junctures, wherein the secondary split and secondary juncture are situated between the inlet header and the outlet header, and wherein a subset of the secondary splits and secondary junctures route fluid through interconnections between fluidly parallel branched channels; wherein the array of branched channels is pattern-less, such that there are no repeating patterns of branched channels, splits, and junctures within the core and the branched channels have varying shapes, sizes, diameters, and outer boundary lengths throughout the array. an inlet header integrally formed with and fluidly connected to the first inlet; an outlet header integrally formed with and fluidly connected to the first outlet; and an array of branched channels connecting the first inlet and to the first outlet, wherein the external casing and an exterior surface of the array of branched channels define a fluidic passage between the second inlet and the second outlet, wherein the array of branched channels comprises: 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; characterized by a secondary branching structure including one or more secondary splits and one or more secondary junctures, wherein the secondary split and secondary juncture are situated between the inlet header and the outlet header, and wherein a subset of the secondary splits and secondary junctures route fluid through interconnections between fluidly parallel branched channels; wherein the array of branched channels is pattern-less, such that there are no repeating patterns of branched channels, splits, and junctures within the core and the branched channels have varying shapes, sizes, diameters, and outer boundary lengths throughout the array. 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; characterized by a secondary branching structure including one or more secondary splits and one or more secondary junctures, wherein the secondary split and secondary juncture are situated between the inlet header and the outlet header, and wherein a subset of the secondary splits and secondary junctures route fluid through interconnections between fluidly parallel branched channels; wherein the array of branched channels is pattern-less, such that there are no repeating patterns of branched channels, splits, and junctures within the core and the branched channels have varying shapes, sizes, diameters, and outer boundary lengths throughout the array.