Axial-flow fan

Abstract

An axial-flow fan includes an impeller mounted on a rotating shaft of a rotary drive device and a venturi casing surrounding an outer periphery of the impeller in a radial direction and including a suction port and a discharge port facing each other in an axial direction of the rotating shaft . An inner surface of the venturi casing includes a suction-side slant part 31 expanding the suction port outward in the radial direction of the impeller, a linear part continuing from the suction-side slant part and forming an axial flow of a fluid with the impeller, a discharge-side slant part 34 expanding the discharge port outward in the radial direction of the impeller, and a curved part connecting the linear part and the discharge-side slant part.

What is claimed is: 
     
         1 . An axial-flow fan comprising:
 an impeller mounted on a rotating shaft of a rotary drive device; and   a venturi casing surrounding an outer periphery of the impeller in a radial direction and including a suction port and a discharge port facing each other in an axial direction of the rotating shaft, wherein   an inner surface of the venturi casing includes
 a suction-side slant part expanding the suction port outward in the radial direction of the impeller, 
 a linear part continuing from the suction-side slant part and forming an axial flow of a fluid with the impeller, 
 a discharge-side slant part expanding the discharge port outward in the radial direction of the impeller, and 
 a curved part connecting the linear part with the discharge-side slant part. 
   
     
     
         2 . The axial-flow fan according to  claim 1 , wherein
 a boundary between the linear part and the curved part is positioned on a static pressure boundary line between a suction-side static pressure and a discharge-side static pressure of the impeller.   
     
     
         3 . The axial-flow fan according to  claim 1 , wherein
 an inner diameter of the discharge port expanded by the discharge-side slant part is larger than an inner diameter of the suction port expanded by the suction-side slant part.   
     
     
         4 . The axial-flow fan according to  claim 1 , wherein
 the discharge-side slant part expands the discharge port outward in the radial direction of the impeller from the curved part in a linear manner.