A heat exchanger includes a separator member that divides a first flow passage from a second flow passage. The heat exchanger also includes a plurality of first hollow members that extend across the first flow passage at respective non-orthogonal angles. The plurality of first hollow members are fluidly connected to the second flow passage. Moreover, the heat exchanger includes a plurality of second hollow members that extend across the second flow passage at respective non-orthogonal angles. The plurality of second hollow members are fluidly connected to the first flow passage.