Question

A steam radiator in a room at 25°C has saturated water vapor at 110 kPa flowing through it, when the inlet and exit valves are closed. What is the pressure and the quality of the water, when it has cooled to 25°C? How much work is done?

Answer 1

Control volume radiator. 

After the valve is closed no more flow, constant volume and mass.

1:   x₁ = 1, P₁ = 110 kPa ⇒ v₁ = v_g = 1.566 m³/kg 

2:   T₂ = 25°C, ? 

Process:  v₂ = v₁ = 1.566 m³/kg = [0.001003 + x₂ × 43.359] m³/kg 

x₂ = 1.566 – 0.001003/43.359 = 0.0361

State 2 : T₂ , x₂ ,    P₂ = P_sat = 3.169 kPa 

 ₁W₂ =  ∫ PdV = 0