Patent ID: 8764375

Claim:
A counter-rotating axial flow fan comprising: a casing including an air channel having a suction port on one side in an axial direction and a discharge port on the other side in the axial direction; a front impeller including a plurality of front blades and configured to rotate in the air channel; a rear impeller including a plurality of rear blades and configured to rotate in the air channel in a direction opposite to a direction of rotation of the front impeller; and a plurality of support members formed by a plurality of stationary blades or a plurality of struts disposed to be stationary between the front impeller and the rear impeller in the air channel, wherein defining the number of the front blades as N, the number of the support members as M, and the number of the rear blades as P, N, M, and P each being a positive integer, and defining the maximum axial chord length of the front blades as Lf, the maximum axial chord length of the rear blades as Lr, the outside diameter of the front blades as Rf, and the outside diameter of the rear blades as Rr, Lf, Lr, Rf, and Rr each being a positive integer, the following relationships are satisfied: N≧P>M ; and at least one of Lf/(Rf×π/N)≧1.25 and Lr/(Rr×π/P)≧0.83; defining the rotational speed of the front impeller as Sf and the rotational speed of the rear impeller as Sr, a relationship of Sf>Sr is satisfied; and, the following relationships are further satisfied: 5≦ N≦ 7,4≦ P≦ 7,and 3≦ M≦ 5; 1> Lr/Lf> 0.45; and Lf /( Rf×π/N )> Lr /( Rr×π/P ).