Bi-directional fan having asymmetric, reversible blades

摘要

A bi-directional fan includes asymmetrically-shaped fan blades wherein, at each transverse cross-section of the blade, the profile of the blade includes a leading portion lying on one side of a straight line connecting the leading and trailing edges of the blade and a trailing portion lying on the opposite side of the straight line. The leading portion of the blade is larger than the trailing portion of the blade, and the point at which the blade's mean line of profile crosses the straight line is closer to the trailing edge than the leading edge. From the leading edge to a point of maximum camber, the shape of the profile of the blade is described by a polynomial expression. From the point of maximum camber to the trailing edge, the shape of the profile of the blade is described by a cosine wave function. The larger leading portion presents a greater forward-curved surface area which allows the blade to move air more efficiently in the forward direction. While the efficiency of the asymmetric fan blade is reduced in the reverse direction, when the fan is used in the forward direction more than 50% of the time, the overall efficiency of the asymmetric-blade fan is greater than that of the symmetric-blade fan. Each asymmetric fan blade can assume either of two oppositely-oriented positions, allowing one set of identical blades to provide a range of different forward and reverse air flow efficiencies.