FISCHER PRO-LINE DE90 Operating Manual page 59

FISCHER Mess- und Regeltechnik GmbH
BA_EN_DE90
Volume flow measurement at the inlet cone
suction chamber
q: volume flow
k: calibration factor
Δp: differential pressure
ρ: density
c: flow coefficient
D: diameter
basic formula
Fig. 78: Volume flow measurement
Fans are usually equipped with an inlet cone. The volume flow measurement
consists of one or more measuring points in the inlet cone and one measuring
point in the suction chamber of the ventilation unit. The differential pressure
between the measuring points is used to calculate the volume flow.
The basic formula given applies to a frictionless and loss-free flow with constant
density. In reality, therefore, a correction value caused by the design and other
factors must be taken into account.
The fan manufacturers have determined the correction value for each inlet
nozzle. In general, these values are called calibration factor or K-factor and can
be found in the data sheet or operating instructions of the volume flow measur-
ing device.
inlet cone
D
Δp
2
π
q = c
2
D Δp
4 ρ
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