1 kg of nitrogen (N2) gas at 140 K and 10 MPa undergoes a Joule-Thomson expansion to 1 MPa. For this purpose a throttle valve is used and the expansion happens rapidly and adiabatically. For the above system,

a) Show that Joule-Thomson expansion is an isenthalpic process.

b) Calculate the enthalpy and temperature of nitrogen, and the fraction of vapour and liquid, leaving the throttle valve by using the nitrogen pressure-

enthalpy diagram provided.

c) Calculate how much heat needs to be removed from nitrogen after it has undergone Joule-Thomson expansion as explained in a) to achieve full

liquefaction at the same pressure, i.e. 1MPa.

20 THERMODYNAMIC PROPERTIES OF NITROGEN 1 003 10 O 8 6 3 0.014 4 Jo.03 2 005 P, MPa 1 0.8 0.6 10.2 0.4 $-3.75 kJ/(kg-K) - -0.3 m/kg 0.2 +0. +0.1 500 0 50 100 150 200 350 400 450 250 300 , kJ/kg