Problem 6.3 - Adiabatic Efficiency of a Power Plant Feedwater Pump

Recall the steam power plant of Example 4.1 in Chapter 4b. Assume that the pump is adiabatic and that the temperature of the water increases by 0.5°C due to friction as it passes through the pump, as in the following figure:

Under these conditions (10 MPa, 40°C) we normally treat liquid water as an incompressible liquid. Determine:the pump adiabatic efficiency (η_P) defined as the isentropic pump work divided by the actual pump work required to drive the pump. [η_P = 83%]

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

where C_H2O = 4.18 kJ/kg.K and specific volume v = 0.001 m³/kg.
Thus for the isentropic process: (Δs = 0) ⇒ T₂ = T₁ (ΔT = 0). _____________________________________________________________________________________