Fan impeller and heat dissipating device having the same

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.