| 摘要 |
A leading edge (12a) of a rotating blade (12) of an impeller (10) is formed in an arc recessed in a direction opposite to a rotating direction of the impeller. An angle (¸ 1 ) where an extended line of the recessed arc of the leading edge (12a) meets another extended line of a curve of a side edge (12b) is set in an acute angle of 30 to 37 degrees in a front view so that a leading tip of the rotating blade may be projected in the rotating direction. An opening angle (¸ 3 ) of a suction-side slant portion (31) of a venturi casing is set in the range of 12 to 17 degrees and an opening angle (¸ 4 ) of a discharge-side slant portion (33) is set in the range of 30 to 35 degrees. |
