Abstract: An axial flow fan assembly includes a plurality of fan blades surrounded by a shroud. The shroud includes an annular first wall which extends radially outwardly, an annular second wall which extends axially and radially outwardly, and an annular third wall which joins the first wall to the second wall. The third wall has a curved cross sectional shape, and has a minimum diameter part which is positioned approximately half-way between the upstream and downstream edges of the fan blades. There is a desired relationship between the radius of curvature of the third wall and the diameter of the fan. There is a desired relationship between the height of the first wall and the diameter of the fan. The fan blades have an upstream edge which is upstream with respect to the first wall.

Abstract: An axial flow fan assembly includes a plurality of fan blades surrounded by a shroud. The shroud includes an annular first wall which extends radially outwardly, an annular second wall which extends axially and radially outwardly, and an annular third wall which joins the first wall to the second wall. The third wall has a curved cross sectional shape, and has a minimum diameter part which is positioned approximately half-way between the upstream and downstream edges of the fan blades. There is a desired relationship between the radius of curvature of the third wall and the diameter of the fan. There is a desired relationship between the height of the first wall and the diameter of the fan. The fan blades have an upstream edge which is upstream with respect to the first wall. The third wall has a minimum diameter part which is positioned approximately half-way between the upstream and downstream ends of the fan.