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Flow coefficient

The flow coefficient (φ) is a dimensionless quantity used to describe the volume flow rate. It is also referred to as the volume or volume flow coefficient and characterises the flow rate (Q). Durchflusszahl_Formel_1

When the flow rate varies at constant rotational pump speed, vm ~ Q and therefore φ ~ Q.

The flow coefficient (φ) is therefore indicative of the abscissa (analogous to Q) on H/Q curves plotted in non-dimensional representation. With reference to the vane inlet and outlet diameters, the following equations are obtained:

Durchflusszahl_Formel_2

With regard to the head coefficient, it is preferable to adopt the flow coefficient related to the impeller outlet.