Five types of centrifugal fans were tested at a number of speeds. Included were several geometrically similar fans of different sizes. Dimensionless total pressure and efficiency were plotted against dimensionless flow for each of the Reynolds numbers tested. It was found that for most fan types there exists a threshold Reynolds number. Above this threshold value fan performance is essentially independent of Reynolds number. Below this threshold value fan performance varies with Reynolds number. It is thus shown that a relationship among three dimensionless groups is a more general description of fan performance than the commonly used relationships between two dimensionless groups.

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