The fluid path through the impeller is in a direction essentially at right angles to its axis both entering and leaving the impeller at its periphery. The impeller otherwise resembles a multivane forward curved centrifugal but has no side entries. Flow is induced by a vortex formed within the impeller.
Apart from structural considerations, there are no limitations on width so that it may be used to give a wide stream from a small diameter e. g., as in a unit heater. See Figures 1.100 and 1.101.
The circulation of air in the toric casing is helicoidal. Rotation of the impeller, which has a number of blades, creates this helicoidal trajectory, which is intercepted by one or more blades depending on the flowrate.
The impeller transfers its energy to the air or gas in the manner shown in Figure 1.102 and is best used for very low flows at high pressure albeit at only a moderate efficiency.
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