Patent ID: 7942627

Claim:
A serial axial fan unit comprising: a first impeller including a plurality of first blades arranged side-by-side in a circumferential direction and centered about a central axis, the first blades extending radially outward; a first motor portion arranged to rotate the first impeller about the central axis; a second impeller including a plurality of second blades arranged side-by-side in the circumferential direction and centered about the central axis, the second blades extending radially outward, the second impeller being arranged in series with the first impeller along the central axis; a second motor portion arranged to rotate the second impeller about the central axis; a flow control device arranged between the first impeller and the second impeller; and a housing arranged to surround the first impeller and the second impeller to define a path for a flow of air; wherein rotation of the first impeller and a rotation of the second impeller causes the air to flow in substantially the same direction; the flow control device includes a plurality of flow control vanes, each of the flow control vanes having a first edge arranged on the first impeller side and a second edge arranged on the second impeller side, the first edge having a portion arranged downstream of the second edge with respect to a rotation direction of the second impeller; the housing includes a first housing portion arranged to surround the first impeller, a second housing portion arranged to surround the second impeller, and a wind tunnel portion arranged to surround the plurality of flow control vanes; the first motor portion is supported by the first housing portion by a plurality of first support ribs extending from the first motor portion radially outward and connected to the first housing portion; the second motor portion is supported by the second housing portion by a plurality of second support ribs extending from the second motor portion radially outward and connected to the second housing portion; each of the plurality of first support ribs has a surface directed upstream with respect to a rotation direction of the first impeller and being curved or slanted toward the second impeller with respect to a direction parallel or substantially parallel to the central axis; and the plurality of flow control vanes and the plurality of first support ribs are equal in number, and the first and second edges of each of the plurality of flow control vanes substantially overlap with each other in the direction parallel or substantially parallel to the central axis when viewed from a direction of the first impeller.