Answer to Question #177186 in Mechanical Engineering for aakah

Question

 Steam at 15 bar is passed through a throttle valve with a pressure drop of 12 bar. The temperature after throttling is 150 °C.

Q.4 The dryness fraction before throttling is

Answer 1

Let ,

p₁= inlet pressure=15 ×10^-6 Pa

x₁ = Quality of steam at inlet

T₁= inlet temperature

h₁ = Inlet specific enthalpy

p₂= Exit pressure=3 ×10^-6 Pa

T₂= Temperature at exit=150 C

h₂=specific Enthalpy at exit.

At T₂= 150 C and P₂=3 bar we can find specific Enthalpy from steam table,

h₂=2571 KJ/kg

Since, during throttling process, enthalpy remains constant,

h₁=h₂=2571 kJ/kg

At inlet pressure P₁=15 bar , h_f=844.56 kJ/kg, h_fg= 1946.4 kJ/kg

h₁=h_f+X h_fg=2571

844.56+X (844.56)=2571.4

X=0.887

Answer:

Dryness fraction of steam at inlet

X=0.887