Question

A boiler feed pump delivers 0.05 m3/ of water at 240°C, 20 MPa. What is the mass flowrate (kg/)? What would be the percent error if the properties of saturated liquid at 240°C were used in the calculation? What if the properties of saturated liquid at 20 MPa were used?

Answer 1

State 1: (T, P) compressed liquid v = 0.001205 m3/kg

m = V/v = 0.05/0.001205 = 41.5 kg/*

vf (240°C) = 0.001229 m3/kg ⇒ m = 40.68 kg/* error 2%

vf (20 MPa) = 0.002036 m3/kg ⇒ m = 24.56 kg/* error 41%

The constant T line is nearly vertical for the liquid phase in the P-v diagram. The state is at so high P, T that the saturated liquid line is not extremely steep.