Casing for a heat-dissipating fan

Abstract

A casing for a heat-dissipating fan defines a space having an air inlet and an air outlet. A bottom plate is provided in the air outlet. The bottom plate rotatably supports a fan wheel having a hub and a plurality of blades extending outward from the hub. An annular wall is formed on the bottom plate and has an outer wall face that tapers gradually toward the bottom plate to form a conic shape.

What is claimed is:  
     
         1 . A casing for a heat-dissipating fan, the casing defining a space having an air inlet and an air outlet, a bottom plate being provided in the air outlet, the bottom plate being adapted to rotatably support a fan wheel having a hub and a plurality of blades extending outward from the hub, an annular wall being formed on the bottom plate and having an outer wall face that tapers gradually toward the bottom plate.  
     
     
         2 . The casing for a heat-dissipating fan as claimed in  claim 1 , wherein the annular wall is conic.  
     
     
         3 . The casing for a heat-dissipating fan as claimed in  claim 1 , wherein the annular wall includes a top that is adjacent to but not in contact with a bottom of the hub, leaving a minimized gap between the hub and the annular wall.  
     
     
         4 . The casing for a heat-dissipating fan as claimed in  claim 1 , wherein the outer wall face of the annular wall is at an acute angle of 60°-80° with a plane on which the bottom plate lies.  
     
     
         5 . The casing for a heat-dissipating fan as claimed in  claim 1 , wherein the outer wall face of the annular wall is inclined.  
     
     
         6 . The casing for a heat-dissipating fan as claimed in  claim 1 , wherein the outer wall face of the annular wall has an arcuate portion adjacent to the bottom plate.  
     
     
         7 . The casing for a heat-dissipating fan as claimed in  claim 1 , wherein the annular wall has a maximum outer diameter not greater than a diameter of the hub.