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 m
3
/kg.
Thus
for the isentropic process: (Δs = 0) ⇒ T
2
= T
1
(ΔT
= 0).