Question

Saturated liquid water at 60 bar is heated until the quality is 43%.

Calculate the amount of heat (kJ/kg) that needs to add into the system.

Answer 1

State 1:

Saturated liquid water at 60 bar. From steam table following properties can be found:

v₁ = 0.001319 m³/kg     h₁ = 1213.32 kJ/kg, T₁ = 275.64 ^oC

Now this sytem is heated utill the quality is 43%

State 2: P₂ = 60 bar, T₂ = 275.64 ^oC and x = 0.43

h₂ =(1-x)h_l+xh_v = (0.57 x 1213.32)+(0.43 x 2784.33) = 1888.85 kJ/kg

Since the process is a constant pressure process, the heat transfer will be equalt to change in enthalpy, thus

Q = h₂ - h₁ = 1888.85 - 1213.32 = 675.53 kJ/kg