H2O in a freemoving insulated closed pistoncylinder fitted w

H2O in a free-moving, insulated, closed piston-cylinder, fitted with a paddle wheel is initially a saturated liquid at 2 bar. It undergoes an irreversible process until it is a saturated vapor (the process is irreversible, but the initial and final states are equilibrium).

(a) Find the work transfer w1-2 (kJ/kg).

(b) Find the entropy generated per unit mass, Sgen/m (kJ/kg K)

Solution

(a)     h2 ( @ 2 bar & x =1 )   = 2710 kJ/kg

         h1 ( @ 2 bar & x =0 )   = 505 kJ/kg

        u2 ( @ 2 bar & x =1 )   = 2530 kJ/kg

        u1 ( @ 2 bar & x =0 )   =504 kJ/kg

        Work transfer   = h2 - h1

                               = (2710 - 505)     =   2205 kJ/kg

b ) Entropy change   s2 - s1   =   7.13    - 1.53    = 5.6 kJ/kg-K