Centrifugal fan

Abstract

There is provided a centrifugal fan including an upper casing which has an air suction opening, a lower casing, and an impeller which is disposed between the upper casing and the lower casing. The impeller includes an upper shroud which is provided on an upper casing side, and a plurality of blades which are arranged along a circumference direction below the upper shroud, and is rotatable around a rotary shaft. A pressure surface of each of the plurality of blades has a convex shape in a rotation direction and is formed with a plurality of protrusions which extend in parallel with the rotary shaft.

What is claimed is: 
     
         1 . A centrifugal fan comprising:
 an upper casing which has an air suction opening;   a lower casing; and   an impeller which is disposed between the upper casing and the lower casing,   wherein the impeller includes an upper shroud which is provided on an upper casing side, and a plurality of blades which are arranged along a circumference direction below the upper shroud, and is rotatable around a rotary shaft, and   wherein a pressure surface of each of the plurality of blades has a convex shape in a rotation direction and is formed with a plurality of protrusions which extend in parallel with the rotary shaft.   
     
     
         2 . The centrifugal fan according to  claim 1 ,
 wherein the plurality of protrusions are densely formed in an area in the vicinity of a leading edge of each blade and not formed in an area in the vicinity of a base part of each blade.   
     
     
         3 . The centrifugal fan according to  claim 1 ,
 wherein the upper casing and the lower casing configure an open-type casing,   wherein the impeller further includes a lower shroud which is provided below the plurality of blades,   wherein an outside diameter of the lower shroud is equal to or smaller than an inside diameter of the upper shroud, and   wherein an inside portion of each of the blades has an inclined portion which connects an inside circle portion of the upper shroud and an inside circle portion of the lower shroud.