A device for transferring heat between a first fluid and a second fluid, the device comprising: a set of nested tubular walls (238a-f); a plurality of helical walls intersecting each of the nested tubular walls to form one or more first channel layers nested with one or more second channel layers, each first channel layer and each second channel layer including a plurality of helical fluid channels; a first intake and a first outtake in fluid communication with one another via the plurality of helical fluid channels of each first channel layer, for flow of the first fluid through the device from the first intake to the first outtake; a second intake and a second outtake in fluid communication with one another via the plurality of helical fluid channels of each second channel layer, for flow of the second fluid through the device from the second intake to the second outtake; a first inflow manifold providing fluid communication between the first intake and each helical fluid channel of the plurality of helical fluid channels of each first channel layer, the first inflow manifold including a plenum and a distribution channel extending from the plenum, the plenum being in direct fluid communication with only a subset of the plurality of helical fluid channels of a first channel layer of the one or more first channel layers, the distribution channel providing fluid communication between the plenum and another subset of the plurality of helical fluid channels of the first channel layer of the one or more first channel layers; a second outflow manifold located adjacent the first inflow manifold and including a plenum, the second outflow manifold providing fluid communication between each helical fluid channel of the plurality of helical fluid channels of each second channel layer and the second outtake; and an end cap (276a,b) located at an inlet end of the first channel layer of the one or more first channel layers, the end cap forming a wall of the distribution channel of the first inflow manifold and separating the plenum of the second outflow manifold from the distribution channel of the first inflow manifold, wherein the set of nested tubular walls defines a central axis, and wherein the first intake, the first outtake, the second intake, and the second outtake define respective axes that are parallel to the central axis. a set of nested tubular walls (238a-f); a plurality of helical walls intersecting each of the nested tubular walls to form one or more first channel layers nested with one or more second channel layers, each first channel layer and each second channel layer including a plurality of helical fluid channels; a first intake and a first outtake in fluid communication with one another via the plurality of helical fluid channels of each first channel layer, for flow of the first fluid through the device from the first intake to the first outtake; a second intake and a second outtake in fluid communication with one another via the plurality of helical fluid channels of each second channel layer, for flow of the second fluid through the device from the second intake to the second outtake; a first inflow manifold providing fluid communication between the first intake and each helical fluid channel of the plurality of helical fluid channels of each first channel layer, the first inflow manifold including a plenum and a distribution channel extending from the plenum, the plenum being in direct fluid communication with only a subset of the plurality of helical fluid channels of a first channel layer of the one or more first channel layers, the distribution channel providing fluid communication between the plenum and another subset of the plurality of helical fluid channels of the first channel layer of the one or more first channel layers; a second outflow manifold located adjacent the first inflow manifold and including a plenum, the second outflow manifold providing fluid communication between each helical fluid channel of the plurality of helical fluid channels of each second channel layer and the second outtake; and an end cap (276a,b) located at an inlet end of the first channel layer of the one or more first channel layers, the end cap forming a wall of the distribution channel of the first inflow manifold and separating the plenum of the second outflow manifold from the distribution channel of the first inflow manifold,