Liquid nitrogen is useful for medical purposes and for research laboratories. Determine the minimum shaft work needed to liquefy nitrogen initially at 298 K and 0.1013 MPa and ending with saturated liquid at the normal boiling point, 77.4 K and 0.1013 MPa. The heat of vaporization at the normal boiling point is 5.577 kJ/mol, and the surroundings are at 298 K. The constant pressure heat capacity of gaseous nitrogen can be assumed to be independent of temperature at 7/ 2R for the purpose of this calculation.
(a) Consider nitrogen entering a flow device at 1 mol/min. Give shaft work in kW.
(b) Consider nitrogen in a piston/cylinder device. Give the work in kJ per mole liquefied.
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(c) Compare the minimum shaft work for the two processes. Is one of the processes more advantageous than the other on a molar basis?