Additional Problem 6.4 - Feedwater Pump of the Gavin Power Plant

In the Gavin Power Plant, each generating system has a single-stage feedwater pump driven by a steam turbine, as shown below. Its purpose is to pump the condensed saturated-liquid water at 10 kPa to a high pressure of 25 MPa at the inlet to the boiler. The pump is powered by a dedicated 48.49 MW (65,000 hp) turbine. Assume that the pump is adiabatic and that the temperature of the water increases by 0.8°C due to friction as it passes through the pump.
Determine:

• a) the actual mass flow rate of the water [1711 kg/s].
• b) the pump efficiency (_P) defined as the isentropic pump work divided by the actual pump work required to drive the pump. [_P = 88%]

Note: In solving this problem we use the following relations for an incompressible fluid:

where C_H2O = 4.18 kJ/kg.K and specific volume v = 0.001 cu.m/kg.
Thus for the isentropic process: