Handbook of Turbomachinery Second Edition Revised - Ventech!

somewhat smaller magnitude of vector C (as well as a change in the direction
of vector C). (The importance of this will become apparent later.)
An H-Q curve can be derived analytically given knowledge of the
pump’s geometry by selecting a flow rate; computing the U, W, and C
vectors; and computing the head rise from Eq. (7). At flow rates
significantly away from the design value, knowledge of various mechanisms
of internal energy loss is also required. These will be covered in subsequent
sections.
A set of correlations known as pump affinity laws is available to enable
easy computation of the performance of a pump at any speed of interest if
the performance at a given speed is known. These affinity laws relate the
flow, developed head, and required power at a new flow rate to that at a
reference flow rate. These affinity laws take the following form:
Where
Q1
Q2
¼ N1
N2
Q ¼ flow rate of the pumped fluid.
N ¼ pump operating speed.
Subscripts 1 and 2 denote the reference condition, and the other condition of
interest, respectively.
Where
Where
H1
H2
¼ N1
N2
2
H ¼ pump developed head, expressed in ft.
P1
P2
¼ N1
N2
3
P is the required pump power.
ð9Þ
ð10Þ
ð11Þ
The Specific speed (N s) parameter has a companion term that is related
to the suction performance requirements (or capabilities) of a rotor or pump
stage. This term is known as the suction specific speed (Nss) and is computed
Copyright © 2003 Marcel Dekker, Inc.