Handbook of Turbomachinery Second Edition Revised - Ventech!

Figure 18 Examples of centrifugal pump stage radial diffuser configurations.
The diffuser incorporating cambered vanes is in common use in rocket
turbopumps. In applications where weight is critical (a not uncommon state
of affairs), the cambered vane diffuser is often preferred since, due to the
vane camber, the radius occupied by the discharge volute can be decreased
somewhat over a pump incorporating a vane island diffuser. This attribute
will decrease the circumference of the volute (usually the portion of the
pump with the thickest walls) and lessen the pump’s weight appreciably.
Regardless of the details of the vane geometry employed, both of these
‘‘radial diffuser’’ configurations have essentially the same objective and
capabilities. The vane row alters the flow’s angular momentum, achieving a
given deceleration and static pressure rise over a much-reduced linear
distance, and with attendant lower losses.
It should be noted here that analysis of the performance of any vaned
diffuser in a centrifugal pump stage is somewhat complicated by the nature
of the flow field entering it. The impeller exit flow field is exceedingly
complex, with multiple embedded secondary flows. For this reason, care
must be used in applying general industrial data from conical diffusers used
in piping networks where the nature of the diffuser inlet flow field is very
different.
As with virtually any design feature that increases efficiency, options
for a vaned diffuser (particularly those incorporating an aggressive amount
of diffusion) should be examined carefully before committing to their
incorporation. Figure 15(g) shows an example of the efficiency character-
Copyright © 2003 Marcel Dekker, Inc.