Abstract: An evaporative cooler including a cross-flow plate heat exchanger formed by a plurality of stacked, fluted plates. The evaporative cooler may be operated in an indirect evaporative cooling process, or in a combined direct and indirect mode. The heat exchanger operates as a cross between a cross-flow exchanger and a counter-flow exchanger because the primary and secondary air streams are not perpendicular or parallel to one another, but rather, are oriented at an oblique angle. In a preferred embodiment formed by stacked hexagonal plates, the shape of the exchanger lends itself to the application of water on a primary side to achieve two-stage (indirect plus direct) evaporative cooling. In the two-stage operation mode, all six sides of the heat exchanger have water flowing through the corrugated flutes.