Problem 3: Refrigerant-134a is throttled from 10 bar and 36 o C to 240 kPa. Heat is lost from the refrigerant in the amount of 1 kJ/kg to the surroundings. Determine the exit temperature of the refrigerant. Assume steady state and ignore kinetic and potential energy effects.

Respuesta :

Answer:

[tex]T_{out} = -5.38\,^{\textdegree}C[/tex]

Explanation:

By applying the First Law of Thermodynamics, the model for the throttle valve is:

[tex]-q_{out} + h_{in} - h_{out} = 0[/tex]

The specific enthalpy at outlet is:

[tex]h_{out} = -q_{out}+h_{in}[/tex]

The state of the refrigerant 134a at inlet is a subcooled liquid. Then, specific enthalpy is:

[tex]h_{in} \approx 137.34\,\frac{kJ}{kg}[/tex]

The specific enthalpy at outlet is:

[tex]h_{out} = -1\,\frac{kJ}{kg}+137.34\,\frac{kJ}{kg}[/tex]

[tex]h_{out} = 136.34\,\frac{kJ}{kg}[/tex]

The substance at outlet is a liquid-vapor mixture. Then, exit temperature is:

[tex]T_{out} = -5.38\,^{\textdegree}C[/tex]