Question

A boiler feed pump delivers 0.05 m³/s of water at 240°C, 20 MPa. What is the mass flowrate (kg/s)? 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/s

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

v_f (20 MPa) = 0.002036 m³/kg ⇒ m = 24.56 kg/s 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.