Blade of axial flow impeller and axial flow impeller

1. A blade connectable to a central hub of an axial flow impeller, the blade being formed from substantially plate-type material and having

a leading edge,

a trailing edge,

a tip,

a root attachable to the central hub of the impeller,

a first fold extending along the blade in a straight first direction and dividing the blade into a first profile portion located adjacent to the leading edge and a second profile portion, the first and the second profile portions meeting at the first fold such that the first profile portion is angled at a first angle (α 1 ) downwardly from the second profile portion,

a second fold extending along the blade in a straight second direction which is different from said first direction and located apart from the first fold and dividing the blade further into a third profile portion located adjacent to the trailing edge, said second and third profile portions meeting at said second fold such that the third profile portion is angled at a second angle (α 2 ) downwardly from the second profile portion, the second profile portion being angled at a third angle (α 3 ) in relation to horizontal plane,

and, in plan view, the blade has the general form of an enveloping rectangle (R×W b ) with tapering cut-outs at at least root-side corners of the rectangle,

said rectangle having a length R which is the lengthwise dimension from the axis of rotation of the impeller to the tip of the blade, and a width W b which is the widthwise dimension of the blade perpendicularly to the lengthwise direction, the enveloping rectangle having inner corners adjacent to the root and outer corners adjacent to the tip, characterized in that the contour of the blade is defined by the proportional dimensions of the tapering cut-outs from the enveloping rectangle, the cutouts comprising

a first cut-out which is adjacent the root and a first inner corner of the rectangle at the side of the leading edge, the first cut-out having a form of a right triangle with the lengthwise cathetus having a dimension A=0.2R, a widthwise cathetus having a dimension B=0.2W b , and a hypotenuse which forms a first cut-out edge of the blade extending from the root to the leading edge,

a second cut-out which is adjacent to the root and a second inner corner of the rectangle at the side of the trailing edge, the second cut-out having a form of a right triangle with the lengthwise cathetus having a dimension C=0.2R, a widthwise cathetus having a dimension D=0.2W b , and a hypotenuse which forms a second cut-out edge of the blade extending from the root to the trailing edge,

a third cut-out which is adjacent to the tip and a first outer corner of the rectangle at the side of the leading edge, the third cut-out having a form of a right triangle with the lengthwise cathetus having a dimension E=0.5R, a widthwise cathetus having a dimension F=(0.1 to 0.2)R and a hypotenuse which forms a third cut-out edge of the blade extending from the leading edge to the tip, the third cut-out edge connecting to the tip with a rounding having a radius of curvature G=0.2W b , and

a fourth cut-out which is adjacent to the tip and a second outer corner of the rectangle at the side of the trailing edge, the fourth cut-out having a form of a right triangle with the lengthwise cathetus having a dimension H=0.25R, a widthwise cathetus having a dimension I=0.1R and a hypotenuse which forms a fourth cutout edge of the blade extending from the trailing edge to the tip, the fourth cut-out edge connecting to the tip with a rounding having a radius of curvature G=0.2W b ;

that the first fold intersects the lengthwise side of the enveloping rectangle at the meeting point of the first cut-out edge and the leading edge at the distance A=0.2R from the first inner corner, and the first fold intersects the widthwise side of the enveloping rectangle adjacent to the tip at the distance J=0.4R from the third corner;

that the second fold intersects the widthwise side of the enveloping rectangle adjacent to the root at a widthwise distance K=0.1W b from the first corner, and the second fold intersects the side of the enveloping rectangle adjacent to the tip at a widthwise distance I=0.1R from the fourth corner;

and that the first angle (α 1 =6°±1°, the second angle α 2 =8°±1° and the third angle α 3 =19° to 25°.

2. The blade according to claim 1 connected to the central hub of an axial flow impeller, the central hub connectable to a rotatable shaft having a central axis of rotation, the axial flow impeller having a second blade according to claim 1 , the blade and the second blade being attached to the central hub and extending radially outwardly from the hub.

3. The blade according to claim 2 , where the impeller comprises at least three equally-spaced said blades.

4. The axial flow impeller according to claim 2 , characterized in that the impeller comprises four or more equally-spaced said blades.