Low noise and high efficiency blade for axial fans and rotors and axial fan or rotor comprising said blade

Abstract

Today the low noise blades and especially the super low noise blades for large diameter axial fans which are employed in the big cooling machines and cooling plants are so costly and are requiring so many extra costs on the other related equipment, that the noise pollution abatement can increase the whole cooling apparatus cost by up to a 35%. This invention, provides a new technology to make low noise fans able to transform any common blade into a low noise or very low noise at very low cost, preserving the same high efficiency and tip speed, as opposite to all the other low noise blades at actual status of art. As the fans for the big cooling apparatus are generally their main noise source, this invention will offer the opportunity to dramatically reduce the noise pollution produced by big cooling machines and cooling plants.

What is claimed is: 
     
         1 . An axial fan, having a large diameter and an adjustable pitch angle, comprising:
 at least one blade comprising a front edge and a rear edge, the front edge being a leading edge of the at least one blade facing a direction of rotation of the axial fan in an operative condition, and the rear edge being a trailing edge of the at least one blade,   the at least one blade further comprising:
 a root portion configured to fix the blade to a rotor of the axial fan; 
 a first blade portion extending from the root portion; and 
 a second blade portion extending from the first portion, 
   wherein a portion of the leading edge defined by the first portion and a portion of the leading edge defined by the second portion extend along different directions and define an obtuse angle so that the projection of the at least one blade on a plane of rotation of the axial fan is V-shaped, and   the trailing edge of the at least one blade is defined by the first portion only.   
     
     
         2 . The axial fan according to  claim 1 , wherein the root portion is shaped so as to define a pitch adjustment axis X-X, and with reference to the pitch adjustment axis X-X, a vertex of an angle defined by the portion of the leading edge defined by the first portion and the portion of the leading edge defined by the second portion lies on one side along with opposite tips of the leading edge. 
     
     
         3 . The axial fan according to  claim 1 , wherein the obtuse angle is in a range between 90° and 170° when considered outside the at least one blade. 
     
     
         4 . The axial fan according to  claim 3 , wherein the obtuse angle is in a range between 100° and 120° when considered outside the at least one blade. 
     
     
         5 . The axial fan according to  claim 1 , wherein at a portion of the at least one blade where the first part and the second part join, a dihedral angle is defined between the first portion and the second portion of the at least one blade. 
     
     
         6 . The axial fan according to  claim 5 , wherein the dihedral angle is in a range between 0° and 20°. 
     
     
         7 . The axial fan according to  claim 1 , wherein the axis X-X of the at least one blade is inclined towards a low-pressure region with respect to the plane of rotation of the axial fan and defines a precone angle. 
     
     
         8 . The axial fan according to  claim 7 , wherein the precone angle is in a range between 0° and 5°. 
     
     
         9 . The axial fan according to  claim 1 , wherein the at least one blade further comprises a tip winglet. 
     
     
         10 . An axial fan, having a large diameter and an adjustable pitch angle, comprising:
 at least one blade comprising a front edge and a rear edge, the front edge being a leading edge of the at least one blade facing a direction of rotation of the axial fan in an operative condition, and the rear edge being a trailing edge of the at least one blade,   the at least one blade further comprising:
 a root portion configured to fix the blade to a rotor of the axial fan; 
 a first blade portion extending from the root portion; and 
 a second blade portion extending from the first portion, wherein a portion of the leading edge defined by the first portion and a portion of the leading edge defined by the second portion extend along different directions and define an obtuse angle so that the projection of the at least one blade on a plane of rotation of the axial fan is V-shaped, and the trailing edge of the at least one blade is defined by the first portion only, and the at least one blade is produced by a process of manufacturing that starts from at least one of extruded or pultruded semifinished products, the process further comprising: 
 cutting the extruded or pultruded semifinished products to obtain at least one of the first blade portion and the second blade portion; 
 joining together the first blade portion and second blade portion; and 
 adding the root portion so as to obtain the at least one blade.