Centrifugal fan and impeller thereof

1. An impeller, comprising:

a hub having a circumferential surface;

a plurality of connecting structures disposed at intervals and on the circumferential surface of the hub, wherein any adjacent two of the plurality of connecting structures define a first minimum distance therebetween on the circumferential surface;

an annular structure connected to the plurality of connecting structures, wherein the annular structure comprises an outer annular surface; and

a plurality of blades disposed at intervals and on the annular structure, wherein any adjacent two of the plurality of blades define a second minimum distance therebetween on the outer annular surface, adjacent two of the plurality of connecting structures defining the first minimum distance are located between the plurality of blades and the hub, a first difference between any two adjacent first minimum distances is different from a second difference between any two adjacent second minimum distances, and a least common multiple of a number of the plurality of blades and a number of the plurality of connecting structures is a product of the number of the plurality of blades and the number of the plurality of connecting structures.

2. The impeller of claim 1 , wherein the number of the plurality of blades is greater than the number of the plurality of connecting structures.

3. The impeller of claim 1 , wherein the number of the plurality of connecting structures is less than or equal to 13, and the number of the plurality of blades is greater than 13.

4. The impeller of claim 1 , wherein two of the plurality of blades farthest from each other define an outer diameter D, and the annular structure has an annular structure outer diameter d, wherein the outer diameter d and the outer diameter D substantially satisfy a relation of 40%×D<d<85%×D.

5. The impeller of claim 1 , wherein each of the plurality of connecting structures has at least one largest surface, and the circumferential surface has a circumferential direction, wherein the circumferential direction is substantially perpendicular to or sloped to the largest surface of each of the plurality of connecting structures.

6. The impeller of claim 1 , wherein each of the plurality of connecting structures has at least one largest surface, and the circumferential surface has a circumferential direction, wherein the circumferential direction is substantially parallel to the largest surface of each of the plurality of connecting structures.

7. The impeller of claim 1 , wherein each of the plurality of connecting structures is flat, blade-shaped or rib-shaped.

8. An impeller, comprising:

a hub having a circumferential surface;

a plurality of connecting structures disposed at intervals and on the circumferential surface of the hub, wherein each of the plurality of connecting structures has two opposite end surfaces, end surfaces of two adjacent connecting structures of the plurality of connecting structures define a first minimum distance on the circumferential surface, the two opposite end surfaces of each connecting structure on the circumferential surface is defined as a second minimum distance, and at least two of the second minimum distances are not equal to each other;

an annular structure connected to the plurality of connecting structures; and

a plurality of blades disposed at intervals and on the annular structure.

9. The impeller of claim 8 , wherein a least common multiple of a number of the plurality of blades and a number of the plurality of connecting structures is a product of the number of the plurality of blades and the number of the plurality of connecting structures.

10. The impeller of claim 8 , wherein a number of the plurality of blades is greater than a number of the plurality of connecting structures.

11. The impeller of claim 8 , wherein a number of the plurality of connecting structures is less than or equal to 13, and a number of the plurality of blades is greater than 13.

12. The impeller of claim 8 , wherein the annular structure has an outer annular surface, wherein any adjacent two of the plurality of blades define a third minimum distance on the outer annular surface, wherein at least two of the third minimum distances are not equal.

13. The impeller of claim 8 , wherein each of the plurality of connecting structures has at least one largest surface, and the circumferential surface has a circumferential direction, wherein the circumferential direction is substantially parallel to the largest surface of each of the plurality of connecting structures.

14. The impeller of claim 8 , wherein each of the plurality of connecting structures is blade-shaped or flat rib-shaped.

15. A centrifugal fan, comprising:

a cover having at least one inlet, an outlet and an accommodating space, wherein the inlet, the accommodating space and the outlet are in spatial communication; and

an impeller accommodated in the accommodating space of the cover, the impeller comprising:

a hub having a circumferential surface;

a plurality of connecting structures disposed at intervals and on the circumferential surface of the hub, wherein any adjacent two of the plurality of connecting structures define a first minimum distance therebetween on the circumferential surface;

an annular structure connected to the plurality of connecting structures, wherein the annular structure comprises an outer annular surface; and

a plurality of blades disposed at intervals and on the annular structure, wherein any adjacent two of the plurality of blades define a second minimum distance therebetween on the outer annular surface, adjacent two of the plurality of connecting structures defining the first minimum distance are located between the plurality of blades and the hub, a first difference between any two adjacent first minimum distances is different from a second difference between any two adjacent second minimum distances, and a least common multiple of a number of the plurality of blades and a number of the plurality of connecting structures is a product of the number of the plurality of blades and the number of the plurality of connecting structures.

16. The centrifugal fan of claim 15 , wherein a number of the at least one inlet is greater than one, and the cover comprises a bottom plate, wherein the bottom plate comprises a plurality of ribs, the at least one inlet is disposed on the bottom plate and are separated by the plurality of ribs, wherein the impeller overlaps with the ribs.

17. A centrifugal fan, comprising:

a cover having at least one inlet, an outlet and an accommodating space, wherein the inlet, the accommodating space and the outlet are in spatial communication; and

an impeller accommodated in the accommodating space of the cover, the impeller comprising:

a hub having a circumferential surface;

a plurality of connecting structures disposed at intervals and on the circumferential surface of the hub, wherein each of the plurality of connecting structures has two opposite end surfaces, end surfaces of two adjacent connecting structures of the plurality of connecting structures define a first minimum distance on the circumferential surface, the two opposite end surfaces of connecting structure on the circumferential surface is defined as a second minimum distance, and at least two of the first minimum distances are not equal to each other, and at least two of the second minimum distances are not equal to each other;

an annular structure connected to the plurality of connecting structures; and

a plurality of blades disposed at intervals and on the annular structure.

18. The centrifugal fan of claim 17 , wherein a number of the at least one inlet is greater than one, and the cover comprises a bottom plate, wherein the bottom plate comprises a plurality of ribs, the at least one inlet is disposed on the bottom plate and are separated by the plurality of ribs, wherein the impeller overlaps with the plurality of ribs.