Patent ID: 7828510

Claim:
A fan, comprising: a casing having a first air-containing portion disposed therein, wherein the air-containing portion comprises a first entrance and a first exit, and the first air-containing portion comprises a first vortex offsetting element for eliminating a vortex caused by air flowing through the first air-containing portion; a first impeller structure installed inside the casing and comprising a first blade set, wherein the first blade set is located corresponding to the first entrance of the first air-containing portion; and a second impeller structure installed inside the casing and comprising a second blade set, wherein the second blade set is located corresponding to the first exit of the first air-containing portion, a diameter of the second impeller structure is greater than that of the first impeller structure, the second blade set and the first vortex offsetting element are interlaced disposed, and the first vortex offsetting element is extended above a part of the second blade set so that the first vortex offsetting element and the second blade set are overlapped along an axial line of the fan, and the first vortex offsetting element and the first blade set are entirely non-overlapped with each other along the axial line of the fan.