Page 281 - Centrifugal Pumps Design and Application

250 Centrifugal Pumps: Design and Application

Figure 14-3. Turbine-type vs. specific speed. The ratio between N S, Q and Ng )BH p
is approximate only, since N S,BHP is a function of turbine efficiency.

Power Output and Affinity Laws

Power output is the rotational energy developed by the HPRT. Its value
in BMP is calculated in a similar manner as for pumps except for the effi-
ciency term.

where Q = Capacity GPM
H = Total head in feet
sp gr = Specific gravity
Et = Overall Efficiency at the turbine mode

Variations in capacity, head, and BHP due to RPM (N) changes can be
determined within reasonable limits by using the affinity laws, which
normally are used for pumps but also apply to HPRT's (described in
Chapter 2).