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3.5 Fan operating points
Decisive for fan design is the operating
point for the specified service data. The
service data are usually the maximum
conditions for the heat flow, temperatures,
safety margins against dirt, and
driving conditions. A suitable fan characteristic
and fan type are selected for
the service data, e. g. for a volume flow
of 25 m 3 /s with a total pressure loss of
1400 Pa (fig. 13). A prerequisite is an
orderly inflow to the fan. This fan selection
procedure is still adequate today
whenever the operating point lies in the
steep section of the characteristic and
in the favourable area of the fan’s characteristic
diagram. Moreover, there
must be no operating conditions that
14
Speed n = [1/min]
D = [mm]
∆ p t in Pa
1800
1600
1400
1200
1000
800
600
1460
3000
2850
2800
2400
B
2000
1800
1500
ηt
D = 1000
0,8
1400
1200
D = 1120
400
10 15 20 25 30 40
V L in m 3 /s
D = 1250
Fig. 13: Excerpt from fan performance graph IN/09V-BF1.
B = Reference point
L = Performance point
ηt = Overall efficiency
∆pt = Total pressure difference = total pressure increase
L
0,85
deviate very much from the design conditions.
The operating point of the fan is determined
taking into account all the components
exposed to the cooling air, inlet
and outlet losses, and all external
influences such as over and underpressures
on the outside of the vehicle.
These are caused by the speeddependent
flow around the vehicle and
by the installation characteristics of the
cooling system (fig. 14). Secondary air
or return flows of hot cooling air may
have an influence on air density at the
cooling air inlet and thus on flow resistance.
This is the case, for instance,
when the air outlet is toward the track
bed.
D = 1400
0,9
IN/09V94
D = 1600
IN/09V00
0,93
IN/09V06
D = 1800
IN/09V12
∆p
in %
100
93,5
88,5
80
70
70
The resistances of wire mesh, filters,
and radiators is easy to calculate. The
calculation of resistance from air-conducting
housing elements, transition
losses from radiator to fan or vice-versa
is possible based on test results or requires
idealized models, e. g. according
to Idelchik [8]. Resistance values
based on experience are also available
for obstacles inside the cooler group,
as in pipes or various other components,
or obstacles downstream of the
cooler group. Where this is not so, fixed
values must be applied. When detailed
calculations are made, the corresponding
inaccuracies will be negligible.
2’
1
3’
100
2
3
108,5 112,5
IN/09V00
V L in %
Fig. 14: Changes of design and performance points with different
systems and operating conditions.
1 – Design point for dirty cooler group with under/overpressure
2’ – Design point for dirty cooler group without under/overpressure
2 – Operating point for dirty cooler group without under/overpressure
3’ – Design point for clean cooler group without under/overpressure
3 – Operating point for clean cooler group without under/overpressure