A heat sink for location in a fluid flow, including a heat sink base and a plurality of heat dissipating elements, such as elongate fins, extending from the surface of the heat sink base. In certain arrangements the heat sink is provided with a diversion flow passageway for diverting a fraction of fluid flow away from the heat dissipating elements. In other arrangements there may be two arrays of elongate fins laterally offset. In yet a further arrangement the heat sink may be configured to promote the generation of at least one vortex.