Fan impeller and heat dissipating device having the same

Abstract

A heat dissipation device includes an electric fan having a fan impeller with a hub and a heat sink. A plurality of main blades and subsidiary blades extend radially and outwardly from the hub and alternate with each other. The electric fan forms an air inlet and an air outlet. The main blades have connecting portions on the hub which are extended towards a center of the hub at the air outlet. The subsidiary blades have a smaller radial length than the main blades. The subsidiary blades each have a connecting edge on the hub which is extended toward the center of the hub adjacent to the air outlet. The fan impeller drives more air to the center of the air outlet, whereby more air can flow to a center of the heat sink.

1 . A fan impeller for generating airflow, comprising:
 a hub forming an air inlet and an air outlet at two opposite sides thereof, the hub having a diameter gradually decreasing along an axial direction from the air inlet towards the air outlet;   a plurality of main blades extending radially and outwardly from an outer circumferential surface of the hub, the main blades each having a connecting edge on the hub, the connecting edge of each main blade extending towards a center of the hub at the air outlet; and   a plurality of subsidiary blades extending radially and outwardly from the outer circumferential surface of the hub, the main blades and the subsidiary blades being alternately arranged around the hub, each of the subsidiary blades having a smaller radial length than each of the main blades, each of the subsidiary blades having a connecting edge on the hub, the connecting edge of the each subsidiary blade extending towards the center of the hub at the air outlet, the main blades and the subsidiary blades cooperatively driving the airflow to a center of the air outlet when the impeller is rotated.   
     
     
         2 . The fan impeller as claimed in  claim 1 , wherein the main blade has a greater axial length than the subsidiary blade. 
     
     
         3 . The fan impeller as claimed in  claim 1 , wherein a radial length of each of the subsidiary blades decreases along an axial direction from the air inlet towards the air outlet. 
     
     
         4 . The fan impeller as claimed in  claim 1 , wherein the hub defines a receiving space adjacent to the air inlet. 
     
     
         5 . The fan impeller as claimed in  claim 4 , wherein the hub is bowl-shaped, the hub forms an inner surface surrounding the receiving space, and a diameter of the receiving space defined by the inner surface decreases along an axial direction from the air inlet towards the air outlet. 
     
     
         6 . A heat dissipating device comprising:
 a heat sink comprising a plurality of heat dissipating fins; and   an electric fan mounted on the heat sink for generating airflow flowing through the fins of the heat sink to take away heat from the heat sink, the electric fan comprising:   a hub forming an air inlet and an air outlet, the air outlet being located between the air inlet and the heat sink, the hub having a diameter gradually decreasing along an axial direction from the air inlet towards the air outlet;   a plurality of main blades extending radially and outwardly from an outer circumferential surface of the hub, the main blades each having a connecting edge on the hub, the connecting edge of each main blade extending towards a center of the hub at the air outlet; and   a plurality of subsidiary blades extending radially and outwardly from the outer circumferential surface of the hub, the blades and the subsidiary blades being alternately arranged around the hub, the subsidiary blades each having a smaller radial length than each of the main blades, the subsidiary blades each having a connecting edge on the hub, the connecting edge of the each subsidiary blade extending towards the center of the hub at the air outlet, the main blades and the subsidiary blades driving the airflow to a center of the air outlet when the impeller is rotated.   
     
     
         7 . The heat dissipating device as claimed in  claim 6 , wherein each of the main blades has a greater axial length than each of the subsidiary blades. 
     
     
         8 . The heat dissipating device as claimed in  claim 6 , wherein a radial length of each of the subsidiary blades decreases along an axial direction from the air inlet towards the air outlet. 
     
     
         9 . The heat dissipating device as claimed in  claim 6 , wherein an end of the hub defines a receiving space adjacent to the air inlet. 
     
     
         10 . The heat dissipating device as claimed in  claim 9 , wherein the hub is bowl-shaped, and the hub forms an inner surface surrounding the receiving space, and a diameter of the receiving space defined by the inner surface decreases along an axial direction from the air inlet towards the air outlet.