A heat exchanger comprising a substrate that comprises a bottom side and a top side; a unit for generating a directed fluid stream with a flow direction that is tangential to the bottom side and to the top side of substrate; webs projecting from the top side of substrate and perpendicular to the flow direction, lying one after the other in the flow direction, wherein a height of the webs is less than a spacing of adjacent webs in the flow direction; and a plurality of regularly arranged channels extending through the substrate.