Mixed Flow Fans — Comparative Investigations of Blade Design Methods

Abstract

According to the direction of flow, fans can be classified in the following three types: axial, mixed flow and radial fans. If large volume flows are required with a proportionally high pressure increase, mixed flow fans can be used. Similar to axial fans, mixed flow fans provide a large flow rate and because of the radial portion in the flow deflection they increase the pressure ratio. Contrary to axial and radial fans, in technical literature there are only a few recommendations concerning the design method of mixed flow fans available. The present study focuses on the comparative research of four different blade design methods adapted to mixed flow fans. The selected methods created a straight blade, a profiled blade, a foreward curved “Engelberg” blade and a backward curved “Pfleiderer” blade. The contour of the hub and shroud remained unchanged during the entire design process as a fixed parameter. The 4 different blade sets were manufactured and experimentally tested on a suction side chamber test stand according to DIN EN ISO 5801. The measurement results show, for comparison, the characteristic curves relating flow rate and pressure increase and the achieved overall efficiencies. Here, the design method of “Pfleiderer” has proved its worth, both through its precise meeting of the design point as well as by achieving the highest efficiency.