Question 7.7: Problem: Superheated water vapour at 0.1 MPa and 250 °C is e...

Problem: Superheated water vapour at 0.1 MPa and 250 °C is expanded in an isentropic process to a temperature of 35 °C. Show that the final state is a saturated mixture and find its quality.

Find: The quality x_2 of the final saturated mixture.

Known: Initial saturation pressure P_{1,sat} = 0.1 MPa, initial saturation temperature T_{1,sat} = 250 °C, final saturation temperature T_{2,sat} = 35 °C, isentropic process.

Properties: From Table 7.4 at P_{1,sat} = 0.1 MPa and T_{1,sat} = 250 °C, specific entropy s_1 = 8.0333 kJ / kgK. From Table 7.2 at T_{2,sat} = 35 °C, specific entropy of liquid s_f = 0.5053 kJ / kg and vapour s_g = 8.3531 kJ / kg.

Table 7.4 Properties of superheated water vapour at 0.1 MPa pressure.

Table 7.2 Properties of saturated water as a function of temperature.