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70
75
80
85
90
95
100
65
60
55
10 15 20 30 40 50 60 70 80 90
n
q
[min
-1
]
η
[%]
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70
75
80
85
90
95
100
65
60
55
10 15 20 30 40 50 60 70 80 90
n
q
[min
-1
]
η
[%]
� � � � � �� �
���
� � � � � ��� � � ��� �
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9595
5.4 Loss distribution as function of specific speed
The ratio between the described mechanical and hydraulic losses depends
on the specific speed n
q
, which describes the shape of the impeller, see sec-
tion 4.6. Figure 5.18 shows how the losses are distributed at the design point
(Ludwig et al., 2002).
Flow friction and mixing loss are significant for all specific speeds and are the
dominant loss type for higher specific speeds (semi-axial and axial impellers).
For pumps with low n
q
(radial impellers) leakage and disk friction on the hub
and shroud of the impeller will in general result in considerable losses.
At o-design operation, incidence and recirculation losses will occur.
5.5 Summary
In this chapter we have described the individual mechanical and hydraulic
loss types which can occur in a pump and how these losses aect flow, head
and power consumption. For each loss type we have made a simple physical
description as well as shown in which hydraulic components the loss typi-
cally occurs. Furthermore, we have introduced some simple models which
can be used for estimating the magnitude of the losses. At the end of the
chapter we have shown how the losses are distributed depending on the
specific speeds.
Figure 5.18: Loss distribution in a centrifugal
pump as function of specific speed n
q
(Ludwig et al., 2002).
Mechanical loss
Leakage loss
Disk friction
Flow friction and mixing losses
Hydraulic eciency