A heat exchanger comprising: a plurality of first flow structures and a plurality of second flow structures , the plurality of first flow structures defining respective first flow passages that are configured to receive flow of a first fluid , the plurality of second flow structures defining respective second flow passages that are configured to receive flow of a second fluid , the plurality of first flow structures and the plurality of second flow structures being in an alternating arrangement, the first flow passages each having a first inlet and a first outlet and configured to direct flow of the first fluid along a first flow axis from the first inlet to the first outlet, and the second flow passages each having a second inlet and a second outlet and configured to direct flow of the second fluid along a second flow axis from the second inlet to the second outlet; a plurality of separator members dividing the first flow passages from adjacent ones of the second flow passages in the alternating arrangement; a plurality of first hollow members extending across one of the first flow passages , the plurality of first hollow members respectively having a first end fixedly attached to one of the plurality of separator members and respectively having a second end fixedly attached to an opposing one of the separator members, the first end fluidly connected to one of the second flow passages , the second end fluidly connected to a neighboring one of the second flow passages, the plurality of first hollow members extending along a respective first cross-flow axis to direct flow of the second fluid from the one of the second flow passages, through the hollow member, to the neighboring one of the second flow passages; characterised in that the first cross-flow axis of different ones of the plurality of first hollow members are disposed at different non-orthogonal angles with respect to the one of the plurality of separator members . a plurality of first flow structures and a plurality of second flow structures , the plurality of first flow structures defining respective first flow passages that are configured to receive flow of a first fluid , the plurality of second flow structures defining respective second flow passages that are configured to receive flow of a second fluid , the plurality of first flow structures and the plurality of second flow structures being in an alternating arrangement, the first flow passages each having a first inlet and a first outlet and configured to direct flow of the first fluid along a first flow axis from the first inlet to the first outlet, and the second flow passages each having a second inlet and a second outlet and configured to direct flow of the second fluid along a second flow axis from the second inlet to the second outlet; a plurality of separator members dividing the first flow passages from adjacent ones of the second flow passages in the alternating arrangement; a plurality of first hollow members extending across one of the first flow passages , the plurality of first hollow members respectively having a first end fixedly attached to one of the plurality of separator members and respectively having a second end fixedly attached to an opposing one of the separator members, the first end fluidly connected to one of the second flow passages , the second end fluidly connected to a neighboring one of the second flow passages, the plurality of first hollow members extending along a respective first cross-flow axis to direct flow of the second fluid from the one of the second flow passages, through the hollow member, to the neighboring one of the second flow passages; characterised in that the first cross-flow axis of different ones of the plurality of first hollow members are disposed at different non-orthogonal angles with respect to the one of the plurality of separator members . <EOS>