Impeller and fan

Abstract

An impeller for a fan, which impeller comprises a hub and one or more blades, wherein at least one blade has a radially inner portion which is aerofoil in section and a centrifugal accelerator portion which extends radially outwardly from the aerofoil portion. The aerofoil portion has a greater angle of attack than the accelerator portion.

1 . An impeller for a fan, which impeller comprises a hub and one or more blades, wherein at least one blade has:
 a radially inner portion which is aerofoil in section; and,   a centrifugal accelerator portion which extends radially outwardly from the aerofoil portion,   wherein the aerofoil portion has a greater angle of attack than the accelerator portion.   
   
   
       2 . A impeller according to  claim 1 , wherein the aerofoil portion is helicoidal in profile. 
   
   
       3 . An impeller according to either  claim 1  or  claim 2 , wherein the leading edge of the blade is substantially straight along the length of the blade. 
   
   
       4 . An impeller according to any one of  claims 1  to  3 , wherein the leading edge of the blade extends substantially tangentially from the hub. 
   
   
       5 . An impeller according to any one of  claims 1  to  4 , wherein the hub has a curved circumferential surface from which the blade depends. 
   
   
       6 . An impeller according to  claim 5 , wherein the accelerator portion of the blade extends outwardly of a peripheral edge of the hub. 
   
   
       7 . An impeller according to any one of  claims 1  to  6 , wherein the blade is twisted about its leading edge. 
   
   
       8 . An impeller according to any one of  claims 1  to  7 , wherein the angle of attack at the aerofoil portion is between 0 and 45°. 
   
   
       9 . An impeller according to any one of  claims 1  to  8 , wherein the angle of attack of the accelerator portion is between 60 and 90°. 
   
   
       10 . An impeller according to any one of  claims 1  to  9 , wherein the impeller has a diameter which is at least quadruple the height of the impeller 
   
   
       11 . A fan comprising an impeller according to any one of  claims 1  to  10  and a housing in which the impeller is mounted for rotation. 
   
   
       12 . A fan according to  claim 11  in which the impeller is mounted within a volute formed within the housing. 
   
   
       13 . A fan according to  claim 11  or  12 , in which the housing has an open outlet throat.