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6 Fans and Flow Control Devices
Simultaneous Variation of Several Parameters
For two similar fans of diameter D 0 and D (Fig. 6.18) rotating at speeds N 0 and N,
respectively, Eqs. 6.19, 6.20 and 6.21 are fulfilled.
Flow rate (Q):
Q = Q 0
D
D 0
3 N
N 0
(6.19)
Pressure (P):
P = P 0
D
D 0
2
N
N 0
2
(6.20)
Power (Pw):
Pw = Pw 0
D
D 0
5
N
N 0
3
(6.21)
Fig. 6.18 Schematization of two similar fans of diameters D 0 and D, rotating at revolutions N 0
and N, respectively
Exercise 6.6 A fan, rotating at 500 rpm, supplies 70 m
3 s
−1 at a pressure of 600 Pa.
Determine:
(a) The system impedance curve; and
(b) The pressure it would be able to deliver at those revolutions, if it provides an
airflow rate of 140 m
3 s
−1 .
Solution
(a) Starting from the characteristic curve of the circuit:
6 Fans and Flow Control Devices
Simultaneous Variation of Several Parameters
For two similar fans of diameter D 0 and D (Fig. 6.18) rotating at speeds N 0 and N,
respectively, Eqs. 6.19, 6.20 and 6.21 are fulfilled.
Flow rate (Q):
Q = Q 0
D
D 0
3 N
N 0
(6.19)
Pressure (P):
P = P 0
D
D 0
2
N
N 0
2
(6.20)
Power (Pw):
Pw = Pw 0
D
D 0
5
N
N 0
3
(6.21)
Fig. 6.18 Schematization of two similar fans of diameters D 0 and D, rotating at revolutions N 0
and N, respectively
Exercise 6.6 A fan, rotating at 500 rpm, supplies 70 m
3 s
−1 at a pressure of 600 Pa.
Determine:
(a) The system impedance curve; and
(b) The pressure it would be able to deliver at those revolutions, if it provides an
airflow rate of 140 m
3 s
−1 .
Solution
(a) Starting from the characteristic curve of the circuit: