Multi-blade fans, such as cross flow fans, sirocco fans, and turbo fans, are used as a blower for an air conditioner.
FIG. 26 shows a wall mounted type air conditioner A using a multi-blade fan as the blower.
The air conditioner A is provided with a main body casing 1. The main body casing 1 is provided with an air intake port 4 in an upper surface, and an air blowing port 5 in a front portion of a lower surface. A heat exchanger 2 and a multi-blade fan 3 are provided within the main body casing 1. The multi-blade fan 3 is arranged between the heat exchanger 2 and the air blowing port 5.
The heat exchanger 2 is constituted by a front side heat exchanging portion 2a arranged near a front face of the main body casing 1, and a back side heat exchanging portion 2b arranged near a back face of the main body casing 1. The back side heat exchanging portion 2b is continuously provided in an upper end of the front side heat exchanging portion 2a. An air passage 6 in which the air sucked from the air intake port 4 flows is provided near a front face of the main body casing 1.
Within the main body casing 1, there are provided a first drain pan 8, a second drain pan 9, a guide portion 10, a reverse flow preventing tongue portion 11, a vertical blade 12, and a horizontal blade 13. The vertical blade 12 and the horizontal blade 13 are provided near the air blowing port 5 within the main body casing 1. The first drain pan 8 is provided for receiving a drain generated on the front side heat exchanging portion 2a. The guide portion 10 is provided for guiding the air blown out of the impeller 7 of the multi-blade fan 3 to the air blowing port 5. The reverse flow preventing tongue portion 11 is provided for preventing a reverse flow of the air blown out of the impeller 7.
In the air conditioner A, the air sucked from the air intake port 4 is cooled or heated at a time of passing through the heat exchanger 2. Further, the air flows through in a direction which is orthogonal to a rotary shaft, on the impeller 7 of the multi-blade fan 3, and is thereafter blown out of the air blowing port 5.
The impeller 7 is provided with a plurality of circular support plates and a plurality of impeller blades 15. The impeller 7 has a forward swept structure. The circular support plates are arranged so as to be in parallel to each other at a predetermined interval along the rotary shaft of the impeller 7. Each of the impeller blades 15 is arranged at a predetermined blade angle with respect to the rotary shaft in an outer periphery of each of the circular support plates.
In the multi-blade fan 3 mentioned above, noise is generated at a time when the air passes through the impeller blade 15 of the impeller 7. Main causes of the noise generation are separation of air stream generated near a negative pressure surface of the impeller blade 15, and a trailing vortex generated near a trailing edge of the blade.
In order to reduce the noise, for example, there have been proposed a method of discontinuously forming notches in a blade edge on an outer side of each of the impeller blades 15 and a method of forming the blade edge of each of the impeller blades 15 as a saw tooth shape (for example, refer to Patent Documents 1 and 2). In accordance with these methods, it is possible to suppress the trailing vortex generated near the trailing edge of the blade at a time when the air blows out, and it is possible to reduce the noise.    Patent Document 1: Japanese Laid-Open Patent Publication No. 3-249400    Patent Document 2: Japanese Laid-Open Patent Publication No. 11-141494