There is a need to reliably predict the performance (efficiency and total pressure rise) of axial fans from model tests not only at the design point but also at part- and overload. The commonly used scale-up formulae give satisfactorily results only near the design point where inertia losses are small in comparison with frictional losses. At part- and overload the inertia losses are dominant and the scale-up formulae so far used fail. This is shown by applying several common scale-up methods in comparison to measured values of two axial model fans with a diameter of 1000 mm respectively 250 mm at different rotational speeds, hence Reynolds-numbers. In addition efficiency split-up for axial fans is shown and compared to former measurements on pumps.

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