Patent attributes
A first motor 25 rotates, in one of two rotating directions, the first impeller 7 including a plurality of front blades 28 in a suction opening portion 15 of a housing 59. The second motor 49 rotates, in the other rotating direction opposite to the one rotating direction, the second impeller 35 including a plurality of rear blades 51 in a discharge opening portion 57 of the housing 59. A plurality of stationary blades 61 are arranged between the first impeller 7 and the second impeller 35 in the housing 59. When the number of the front blades 28 is N, that of the stationary blades 61 is M, and that of the rear blades 51 is P, their relationship is defined as N>P>M. A length L1 of the front blades 28 measured in an axial direction is set longer than a length L2 of the rear blades 51 measured in the axial direction.
