APPENDIX G – Pumps and Turbines
Surge Analysis and the Wave Plan Method
Supplementary Material: Example Problems and Solutions
Appendix G – Problem 31
G.31 Define the radius of gyration associated with a plane surface as well as three-dimensional objA pump is operating at 1800 rpm delivering a flowrate of 2 m3/s at a pressure head of 50m. The combined moment of inertia (of the pump and motor) of this pump is 750 N-m2. The efficiency pertaining to this operation is 77%.
a. Compute the hydraulic torque associated with this operation at 1800 rpm.
b. If the pump is operated at 1750 rpm, what is the associated hydraulic torque assuming that the efficiency remains practically unchanged?
c. If the parameters associated with the operation described in part (a) are rated values of the pump, and the pump is tripped generating unsteady flow conditions, compute the speed of the pump after one computational time step of 0.01s. [Hint: Use Eqs. G.7 and G.8]
d. Repeat part c with computational time steps of 0.001s, 0.002s, 0.005s, 0.02s, and 0.05s.
e. If the moment of inertia of 750 Nm2 was computed based on an empirical relationship and it could potentially be off by ±25% (see Section 7.3, more specifically Figures 7.10 and 7.11), compute the speed of the pump after one computational time step of 0.001s, 0.005s, and 0.01s for both the upper and lower bounds of the combined moment of inertia values.
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