Abstract: An axial flow fan has a hub, an annular shroud extending concentric with the axis of the hub, and a number of fan blades connected at a root end to the hub and having a free tip end extending radially towards the shroud. The blades are designed so that the fan in operation at nominal operating conditions generates a fluid flow in the immediate vicinity after the blades, which includes a core flow that is substantially a forced vortex flow where the tangential flow speed component (c2,u) is proportional with the radial distance (r) from the axis. Equations define the chord angle ? of the blades.