Axial cooling fan shroud

A cooling fan assembly for facilitating the transfer of heat through a heat exchanger, the cooling fan assembly comprising:

• a fan rotatable about an axis of rotation and defining a downstream direction along the axis of rotation, wherein the fan is positioned downstream of the heat exchanger, the fan further including a plurality of fan blades;
• and
• a fan shroud including:
• a barrel concentric with the axis of rotation and encircling the plurality of fan blades, the barrel defining a barrel radius and having a base portion;
• and
• a plenum including a plenum body and at least one skirt, the plenum body coupled to the barrel and having a substantially rectangular planform viewed in the upstream direction, the plenum body defining an effective surface monotonically increasing in upstream distance from the base portion, the at least one skirt extending substantially parallel to the axis of rotation and coupled to the plenum body, the at least one skirt including a substantially rectilinear upstream border having a first end and a second end, and wherein the plenum defines for the at least one skirt:
• a cross section C through the axis of rotation and normal to the skirt;
• a distance D1 between cross section C and the first end of the upstream border, and a distance D2 between cross section C and the second end of the upstream border;
• a distance D3, wherein D3 is equal to the lesser of D1 and D2, or is equal to D1 if D1 equals D2;
• a plane P1 parallel to and offset from cross section C an offset distance DP1 less than D3;
• a plane P2 parallel to and offset from cross section C on the opposite side of cross section C from plane P1 an offset distance DP2 less than D3;
• a plane P3 perpendicular to both cross section C and the axis of rotation and containing a point on the upstream border;
• a plane P4 perpendicular to plane P3 and cross section C and containing a point located on cross section C and on the plenum body;
• a plane P5 parallel to and offset from cross section C an offset distance equal to D3;
• and
• a plane P6 parallel to and offset from cross section C on the opposite side of cross section C from plane P5 an offset distance equal to D3,
• wherein a volume V1 is defined as enclosed by planes P1, P2, P3, P4 and the effective surface, a volume V2 is defined as enclosed by planes P1, P3, P4, P5 and the effective surface, a volume V3 is defined as enclosed by planes P2, P3, P4, P6 and the effective surface, an average cross sectional area A1 is defined as V1/(DP1+DP2), an average cross sectional area A2 is defined as (V2+V3)/((D3−DP1)+(D3−DP2), and wherein A1 is less than A2.