Question

Saturated liquid-vapor mixture of water, called wet steam, in a steam line at 1500 kPa is throttled to 50 kPa and 100°C. What is the quality in the steam line?

Answer 1

Answer:

$x = 0.944$

Explanation:

Steam at outlet is an superheated steam, since $T > T_{sat}$. From steam tables, the specific enthalpy is:

$h_{out}=2682.4\,\frac{kJ}{kg}$

The throttle valve is modelled after the First Law of Thermodynamics:

$h_{in} = h_{out}$

Hence, specific enthalpy at inlet is:

$h_{in}=2682.4\,\frac{kJ}{kg}$

The quality in the steam line is:

$x = \frac{2682.4\,\frac{kJ}{kg}-844.55\,\frac{kJ}{kg}}{2791.0\,\frac{kJ}{kg} - 844.55\,\frac{kJ}{kg} }$

$x = 0.944$